Re: NFB windings, was there a US style and UK style?

[mike s]

On Thursday, May 19, 2011 1:52:19 AM UTC+1, Patrick Turner wrote:
> On May 18, 7:54*pm, mike s > wrote:
> > I have a couple of output transformers with separate feedback windings, and was hoping that one might be a suitable replacement for the failed transformer in the *RCA 82 C4 Monitor Amplifier. *Schematic herehttp://www..waltzingbear.com/Schematics/RCA/BA-4C.htm
> >
> > However it uses a high impedance winding *(1/6th of primary anode-anode), whereas the transformers I have both use low impedance windings, about 1:100. *I have a schematic for a British circuit by P J Baxandall *- last on this page *http://mike.wepoco.com/Home/retro-geekery/valve-amplifiers/other-wire...*which places the feedback winding in series with the input pentode cathode, rather than the high impedance potential divider used in the RCA circuit. *Baxandall claimed to be using a transformer design patented by the BBC (Mayo, Tanner, Ellis). *I've seen the same arrangement used in a Marconi push-pull amplifier.
> >
> > I reckon I'm going to have to adopt the Baxandall arrangement, *but would be interested to learn what others think of these circuits. *Presumably it was amplifiers like this that inspired the rather quirky Quad 2 extra feedback to the output valves.http://www.drtube.com/schematics/quad/quad-22.gif
> >
> > Michael
>
> You won't easily find any "drop in" new replacement OPT which could
> be used in the the circuits by RCA, Peter Baxandall, or Peter Walker
> of Quad.

Quirky old stuff is "my thing", so I stash away old transformers and the like. It does seem however that UK designers took a different tack when designing amps/transformers for this style of feedback. So the vintage British transformers I have won't simply "drop in". I'm OK with that.

>
> All these old circuits have serious shortcomings which are only made
> worse when someone tries to use an unsuitable OPT at home and they do
> not understand how NOT to build an oscillator while trying to build an
> amplifier.
>

Hopefully whatever I pick won't be unsuitable, but is going to need some changes. Perhaps in the end the amount of NFB will need to be reduced.

> You say you "have a couple of OPT" without saying just exactly what
> their specification might be. To know what you are doing, you need to
> know every single bit of information which describes each tranny
> fully. You say your OPT in your RCA monitot amp has failed, so we
> assume it has an open primary or shorted turns.

One half of the primary has failed, so the remaining half allows me to establish the ratios, and resistance, of all windings. So I can't use it - as is, but can learn enough about it to know what's needed.

BREAKING NEWS - I've managed to un-pot it, so will post photos. I might even be able to repair it. Which would be nice.

>
> The Hammond 1650P OPT with 6k6 to 4, 8, 16 ohms will be OK with 6L6,
> 807, 1622 etc, but you will need to addapt the Hammond OPT to the RCA
> circuit you already seem to have.
>
> The RCA circuit has NFB loop with R24, 24k, and R8, 2k7, and we don't
> know how much voltage is generated at the NFB winding across OPT
> terminals 1 to 3.

With the turns ratio I can figure that out, and knowing that with the 24k resistor it is unloaded, which I believe is the design principle of these amps - pure voltage feedback, with close to zero lag.

> The lazy dumb ****wits at RCA ommitted to provide
> us with a more clearly drawn schematic with all the working signal
> voltages for all electrodes and transformer windings. My guess is that

It would have been nice to have the voltages, that's for sure. There are copies of the manual for these amps on the WWW so I might find more info.

> OPT terminal 3 produces a NFB voltage of about 50Vrms to be able to
> supply a high enough FB voltage at V3 6SN7 cathode, maybe 5Vrms, so
> that the amount of NFB is at least 12dB.

I'll let you know when I've done the calcs, but these amps were claimed to have very low noise, so high NFB is to be expected.

>
> A normal OPT with no FB winding and just speaker secondaries could be
> used in the RCA circuit but you'd have to re-arrange the FB network to
> V3 cathode with R24 being a lower value. This will affect the way V3
> cathode is biased; if R24 is made smaller it reduces the total value
> of Rk. Fso if R24 = 4k7, the R8 may need to be increased to 3k3 to
> give the equivalent of what is in the schematic, ie, 2k7 // 24k for
> the dc cathode current, ie, about 2k2.
>
> I'd never ever try Baxandall's circuit, and I'm no great fan of Quad,
> or ANY circuit which employs a "paraphase" input pair or uses the
> output of one triode to drive another as done on the RCA circuit. It
> is always better to employ a LONG TAIL PAIR as in many of my amplifier
> schematics which you may inspect at my website at http://www.turneraudio.com.au

It's interesting that RCA and the BBC in the UK adopted these types of amplifier. Clearly broadcast engineers liked them. I wonder why?

> I've always used NFB applied to a cathode of SE triode input stage
> ahead of an LTP driver stage and this is better because the distortion
> of the input tube is included in the FB and thus reduced along with
> all following stages in the loop. The input tube works at low signal
> levels so second order products are minimal. The Williamson, Leak and
> Radford circuits emboby such principles as I do, but to make the amp
> unconditionally stable regardless of load reactance will challenge
> your abilities sorely unless you have a full understanding of what you
> are doing.
>
> Patrick Turner.

[Patrick Turner]

On May 20, 2:14*am, mike s > wrote:
> On Thursday, May 19, 2011 1:52:19 AM UTC+1, Patrick Turner wrote:
> > On May 18, 7:54*pm, mike s > wrote:
> > > I have a couple of output transformers with separate feedback windings, and was hoping that one might be a suitable replacement for the failed transformer in the *RCA 82 C4 Monitor Amplifier. *Schematic herehttp://www.waltzingbear.com/Schematics/RCA/BA-4C.htm
>
> > > However it uses a high impedance winding *(1/6th of primary anode-anode), whereas the transformers I have both use low impedance windings, about 1:100. *I have a schematic for a British circuit by P J Baxandall *- last on this page *http://mike.wepoco.com/Home/retro-geekery/valve-amplifiers/other-wire...which places the feedback winding in series with the input pentode cathode, rather than the high impedance potential divider used in the RCA circuit. *Baxandall claimed to be using a transformer design patented by the BBC (Mayo, Tanner, Ellis). *I've seen the same arrangement used in a Marconi push-pull amplifier.
>
> > > I reckon I'm going to have to adopt the Baxandall arrangement, *but would be interested to learn what others think of these circuits. *Presumably it was amplifiers like this that inspired the rather quirky Quad 2 extra feedback to the output valves.http://www.drtube.com/schematics/quad/quad-22.gif
>
> > > Michael
>
> > You won't easily find any "drop in" new replacement OPT *which could
> > be used in the the circuits by RCA, Peter Baxandall, or Peter Walker
> > of Quad.
>
> Quirky old stuff is "my thing", so I stash away old transformers and the like. It does seem however that UK designers took a different tack when designing amps/transformers for this style of feedback. *So the vintage British transformers I have won't simply "drop in". *I'm OK with that. *

There have been an amazing number of different amps designed by guys
who yearned to be unique. "Yearning For Uniqueness" would have to an
extremely vain pre-occupation of anyone's mind when we consider the
**** of one man smells almost identically to the **** of the next man
along. We all like redheads, brunnettes, and blondes, and what we do
with them is remarkably similar, ie, the divorce rate in the US is
about the same as in Britain.

But the implementation of any one amplifier idea is often just as
important as the idea itself. Ultralinear was the favourite in the US,
and so was global NFB around 3 gain stages with FB froma speaker
winding to cathode of V1. The Pomms showed how in the Williamson which
was a PP triode thinge which quickly became UL if you wanted it to be
for more power. The americans were fond of power, and their cars were
bigger, waistlines longer, houses bigger and government more
influential after WW2. Everything in the USA had to be bigger
brighter, louder, et all while in Deare Olde England which was savaged
by WW2 things remained GRIM with housing, rates of pay, and standard
of living for far longer than in the US after WW2. With smaller houses
and smaller budgets, only the rich in the UK could buy Quad-II amps
with the luxury of powerful octal based tubes such as KT66. KT88 had
to wait until 1957, 12 years after WW2. It wasa time when interest in
hi-fi was seen by many as vain, vapid, absurd, and eccentric. In my
observations of audiophiles, I can see that not much has changed.

>
> > All these old circuits have serious shortcomings which are only made
> > worse when someone tries to use an unsuitable OPT at home and they do
> > not understand how NOT to build an oscillator while trying to build an
> > amplifier.
>
> Hopefully whatever I pick won't be unsuitable, *but is going to need some changes. *Perhaps in the end the amount of NFB will need to be reduced..

The use of NFB from a dedicated NFB winding which uses fine wire
because there is little current was something major makers never
adopted. Baxandal and Williamson were the most ignored blokes of 1950.
People wanted SIMPLE CHEAP solutions, and these two boffins offered
neither cheap nor simple, and insisted on going the extra country mile
to fetch a bucket full of real hi-fi. Baxandall was brilliant, and his
analysis of the Quad ESL57 requirements of the step up trannies shows
how damn dumb most consequent people were about basic audio LCR ideas.
And many online DIY ppl who have tried to build ESL show how dumb they
continue to be.

Baxandall's amp isn't real bad, but the first input pentode must
produce a voltage large enough to drive one 6L6 grid in beam tetrode
mode with fixed Eg2. The other input pentode operates as an inverting
anode follower with unity gain, but any THD generated in V1 is passed
on to be reproduced in V2. In effect, driver amp distortion is double
that of a single tube, and this defect also occurs in any amp using a
paraphase driver. The Williamson is FAR BETTER amp design than
anything with two pentode input tubes. But in 1950, many designers had
a real bad case of pentoditis, the affliction where blokes chose a
pentode instead of two low µ triodes which give much less THD and
IMD.

>
> > You say you "have a couple of OPT" without saying just exactly what
> > their specification might be. To know what you are doing, you need to
> > know every single bit of information which describes each tranny
> > fully. You say your OPT in your RCA monitot amp has failed, so we
> > assume it has an open primary or shorted turns.
>
> One half of the primary has failed, *so the remaining half allows me to establish the ratios, and resistance, of all windings. *So I can't use it - as is, but can learn enough about it to know what's needed.

Many old OPT have several if not many things missing, which is why I
am not delighted by what I find in old 1950s amps. Missing is enough
primary turns, enough interleaving, thick enough primary wire, decent
insulation with low dielectric constant, enough iron, and low winding
losses. Once you know what could have been done and wasn't done in
1950 just so the boss could buy a decent car, then fascination tends
to fade about OLD JUNK.


>
> BREAKING NEWS - *I've managed to un-pot it, so will post photos. *I might even be able to repair it. *Which would be nice.

Yeah, maube the break is accessible, but most OPTs fuse a winding
somewhere deep inside where windings get hot because someone forgot to
build the amp so it shuts down WHEN an OP tube endures bias failure.
>
>
>
> > The Hammond 1650P OPT with 6k6 to 4, 8, 16 ohms will be OK with 6L6,
> > 807, 1622 etc, but you will need to addapt the Hammond OPT to the RCA
> > circuit you already seem to have.
>
> > The RCA circuit has NFB loop with R24, 24k, and R8, 2k7, and we don't
> > know how much voltage is generated at the NFB winding across OPT
> > terminals 1 to 3.
>
> With the turns ratio I can figure that out, and knowing that with the 24k resistor it is unloaded, which I believe is the design principle of these amps - pure voltage feedback, with close to zero lag.

There will be phase shift depending on where the NFB winding is
located relative to other windings. But if the NFB winding is tightly
coupled to the primary, then possibly the phase shift of the secondary
is avoided, especially if the sec load is a capacitance. So with a FB
winding the amp should be easier to make unconditionally stable with
NFB; no attempt is being made to correct for effects of high lekage
inductance between P and speaker windings. Unless you know the real
sequence and placement of all windings, you cannot be sure the NFB
winding will work any better than just taking NFB from speaker sec
(like everyone else) and to the cathode of V1.


>
> > The lazy dumb ****wits at RCA ommitted to provide
> > us with a more clearly drawn schematic with all the working signal
> > voltages for all electrodes and transformer windings. My guess is that
>
> It would have been nice to have the voltages, that's for sure. *There are copies of the manual for these amps on the WWW so I might find more info.. *

The manuals would help, but you can calculate all the loads and
voltage gains based on 2 6L6 in PP class AB for a max of about 30W. Do
your loadline analysis, and all shall be revealed. I guess about 12dB
of NFB is applied, and that isn't much, and not enough, IMHO,
but if you need about 1.5Vrms applied to an input pentode without NFB
for clipping, then with 20dB NFB FB there will be 15V of input.
The better way to do the business is to arrange the two input pentodes
as a true LTP with CCS common cathode sink. This meant a negative
supply and another pentode in 1955, so it was never done because my
dad's generation were too cashed strapped raising the baby boomer
generation, and they were parsimonious about any expenditure.

But now we'd just use a bjt, but even with a large value R taken to
-400V rails which are easy to make with Si diodes is OK. In 1955,
there were no Si diodes. Freedom of circuit design was severely
curtailed. But when solid state came along, everything changed. Sure
they got freedom, and liberation from guilt about never quite ever
building decent OPTs, but early SS was a horror story, and when
dumper bins filled with ****ed tube amps by 1962, ppl were throwing
the baby out with the bath water.

> > OPT terminal 3 produces a NFB voltage of about 50Vrms to be able to
> > supply a high enough FB voltage at V3 6SN7 cathode, maybe 5Vrms, so
> > that the amount of NFB is at least 12dB.
>
> I'll let you know when I've done the calcs, but these amps were claimed to have very low noise, so high NFB is to be expected.

I've made 55W SE amps with extremely low noise despite no use of loop
NFB. My SE55 with 2 x 845 gave noise = 0.25mV with only 10dB global
NFB. That's -98dB no weighting, referred to clip level. But noise
should be low without regard to SNR, because if you have horn speakers
you still want no audible hum from across the room, ie, less than
0.5mV. Low noise is easily achieved by using remote power supplies and
dc to all input tube heaters, and to cathodes of all OP DHT, if used.

The Williamson was renowned for being quiet. It was recommended that a
remote PSU be used. When stero came along, ppl hated the expense of
yet another two chassis with hot things on it. By then it was 1960,
and they hated replacing 10 year old KT66, so the mono system got
replaced by cool running transistor junk.

A few makers kept the faith after 1960 and continued making tube amps,
and many of these dreary things linger on, often with few saving
graces.


> > A normal OPT with no FB winding and just speaker secondaries could be
> > used in the RCA circuit but you'd have to re-arrange the FB network to
> > V3 cathode with R24 being a lower value. This will affect the way V3
> > cathode is biased; if R24 is made smaller it reduces the total value
> > of Rk. Fso if R24 = 4k7, the R8 may need to be increased to 3k3 to
> > give the equivalent of what is in the schematic, ie, 2k7 // 24k for
> > the dc cathode current, ie, about 2k2.
>
> > I'd never ever try Baxandall's circuit, and I'm no great fan of Quad,
> > or ANY circuit which employs a "paraphase" input pair or uses the
> > output of one triode to drive another as done on the RCA circuit. It
> > is always better to employ a LONG TAIL PAIR as in many of my amplifier
> > schematics which you may inspect at my website athttp://www.turneraudio..com.au
>
> It's interesting that RCA and the BBC in the UK adopted these types of amplifier. *Clearly broadcast engineers liked them. *I wonder why?

But the BBC liked Quad-II and Leak and Radfords also, and didn't
really favour any quirky damn amp.

The engineers didn't have much of a say - what they got was what the
accountants authorised. Engineers were a damn pest, always wanting
bucket fulls of cash for "interesting solutions", eg, we need a 50W
amp. Nope, youse can make do with a 20W amp.

Patrick Turner.






> > I've always used NFB applied to a cathode of SE triode input stage
> > ahead of an LTP driver stage and this is better because the distortion
> > of the input tube is included in the FB and *thus reduced along with
> > all following stages in the loop. The input tube works at low signal
> > levels so second order products are minimal. The Williamson, Leak and
> > Radford circuits emboby such principles as I do, but to make the amp
> > unconditionally stable regardless of load reactance will challenge
> > your abilities sorely unless you have a full understanding of what you
> > are doing.
>
> > Patrick Turner.- Hide quoted text -
>
> - Show quoted text -

[Big Bad Bob]

On 05/20/11 03:22, Patrick Turner so wittily quipped:
> Baxandall's amp isn't real bad, but the first input pentode must
> produce a voltage large enough to drive one 6L6 grid in beam tetrode
> mode with fixed Eg2. The other input pentode operates as an inverting
> anode follower with unity gain, but any THD generated in V1 is passed
> on to be reproduced in V2. In effect, driver amp distortion is double
> that of a single tube, and this defect also occurs in any amp using a
> paraphase driver.

I hadn't heard the term 'paraphase' until you mentioned it, so I did a
bit of online research, found out that I've seen things like that before
and I never liked it done 'that way', but yeah, using PENTODES just
makes everything worse for distortion and potential imbalance. Relying
on the circuit gain characteristics of a tube for your design, or
requiring a balance adjustment to make it work, is just silly. As for
me, I prefer the use of a pair of triodes as a direct coupled
'cathodyne' setup (careful biasing and component choices gives you
pretty good results), though a 'long tail pair with a constant current
on the cathodes' (something you had in one of your amps I think) would
be a good alternative (some additional research suggests the latter
might actually work better in an overdriven guitar amp). The long tail
pair has slight imbalance if you don't get close to a constant current
on the cathode, so the simpler 'cathodyne' splitter gives you better
balance with fewer parts (though it may require series resistors for
downstream grids in case they draw current during overdrive on guitar amps).

anyway, I found a couple of interesting web sites that describe the
various types of phase splitters (among other things)

http://www.freewebs.com/valvewizard/index.html (see index on the left)

also more here

http://www.bonavolta.ch/hobby/en/audio/split.htm


> But in 1950, many designers had a real bad case of pentoditis,
> the affliction where blokes chose a pentode instead of two low µ
> triodes which give much less THD and IMD.

there's a general move to create something 'patentable' so that you have
a portfolio of intellectual property, regardless of whether or not it is
actually better. But in cases where another guy's patent steps on your
design, it might be necessary to go a slightly inferior route to avoid
paying royalties. By now all of those patents are expired.

>>
>>> You say you "have a couple of OPT" without saying just exactly what
>>> their specification might be. To know what you are doing, you need to
>>> know every single bit of information which describes each tranny
>>> fully. You say your OPT in your RCA monitot amp has failed, so we
>>> assume it has an open primary or shorted turns.
>>
>> One half of the primary has failed, so the remaining half allows me to establish the ratios, and resistance, of all windings. So I can't use it - as is, but can learn enough about it to know what's needed.
>
> Many old OPT have several if not many things missing, which is why I
> am not delighted by what I find in old 1950s amps. Missing is enough
> primary turns, enough interleaving, thick enough primary wire, decent
> insulation with low dielectric constant, enough iron, and low winding
> losses. Once you know what could have been done and wasn't done in
> 1950 just so the boss could buy a decent car, then fascination tends
> to fade about OLD JUNK.

old junk indeed. reminds me of those 'low iron' class 'A' transformers
that I swapped the phase on (both sides of course) and saw output where
none was before, apparently due to hysteresis problems, on a late 50's
or early 1960's console stereo system. Funny, though, 2W per channel
just wasn't enough so I bought an old 15W/channel (tube) stereo amp in a
caged chassis and just wired it up inside the cabinet.

/me wonders if you could use a 70V 'line' output as the NFB source with
a few mods to the circuit.

[John Byrns]

In article >,
Big Bad Bob > wrote:

> On 05/20/11 03:22, Patrick Turner so wittily quipped:
> > Baxandall's amp isn't real bad, but the first input pentode must
> > produce a voltage large enough to drive one 6L6 grid in beam tetrode
> > mode with fixed Eg2. The other input pentode operates as an inverting
> > anode follower with unity gain, but any THD generated in V1 is passed
> > on to be reproduced in V2. In effect, driver amp distortion is double
> > that of a single tube, and this defect also occurs in any amp using a
> > paraphase driver.
>
> I hadn't heard the term 'paraphase' until you mentioned it, so I did a
> bit of online research, found out that I've seen things like that before
> and I never liked it done 'that way', but yeah, using PENTODES just
> makes everything worse for distortion and potential imbalance. Relying
> on the circuit gain characteristics of a tube for your design, or
> requiring a balance adjustment to make it work, is just silly.

I prefer the floating paraphase phase inverter as it has many advantages over
other forms of phase inverter. If the inverter tube has sufficient gain,
balance is excellent and no balance adjustment is necessary.

--
Regards,

John Byrns

Surf my web pages at, http://fmamradios.com/

[Big Bad Bob]

On 05/20/11 19:21, flipper so wittily quipped:
> On Fri, 20 May 2011 06:54:32 -0700, Big Bad Bob
> > wrote:
>
>> On 05/20/11 03:22, Patrick Turner so wittily quipped:
>>> Baxandall's amp isn't real bad, but the first input pentode must
>>> produce a voltage large enough to drive one 6L6 grid in beam tetrode
>>> mode with fixed Eg2. The other input pentode operates as an inverting
>>> anode follower with unity gain, but any THD generated in V1 is passed
>>> on to be reproduced in V2. In effect, driver amp distortion is double
>>> that of a single tube, and this defect also occurs in any amp using a
>>> paraphase driver.
>>
>> I hadn't heard the term 'paraphase' until you mentioned it, so I did a
>> bit of online research, found out that I've seen things like that before
>> and I never liked it done 'that way', but yeah, using PENTODES just
>> makes everything worse for distortion and potential imbalance. Relying
>> on the circuit gain characteristics of a tube for your design, or
>> requiring a balance adjustment to make it work, is just silly.
>
> Yes, well, the original Williamson called for a balance control on the
> separate triode voltage amps because their gain is what it is. The
> Williamson looks balanced but unless the triodes are identical, fat
> chance, it isn't. (He later decided GNFB was enough to not need the
> balance pot).
>
> The Baxandall is a floating paraphase, which uses negative feedback.
>
> Look at it again. The second pentode is driven by the difference of
> the two signal paths, the two 470k summing 'sense' resistors, and is
> not operating open loop like the Williamson voltage amp triodes are.

> I used a similar floating paraphase on my "Batman" battery guitar amp
> but used triodes and since they were low gain I 'predisposed' the
> balance to nominal, and let the feedback work around that, but with
> pentodes you have lots of gain for NFB around the phase splitter.

curious, which of these designs gives you the best overall gain,
transient response, overdrive characteristics, and lowest cost (or 'part
count')? Down side for cathodyne is that you have to make sure that the
Rp-Rk never drops below around 50V or so (depending on the tube) in the
worst case voltage swing. Alternative is to put a 2nd set of triodes
between the splitter and the output tubes, but not sure if that adds
potential imbalance or not (you'd have to match more parts again). At
that point I'd do the 'long tail' thing and match the Rp's, and use a
constant current source.

[Patrick Turner]

On May 20, 11:54*pm, Big Bad Bob <BigBadBob-at-mrp3-
> wrote:
> On 05/20/11 03:22, Patrick Turner so wittily quipped:
>
> > Baxandall's amp isn't real bad, but the first input pentode must
> > produce a voltage large enough to drive one 6L6 grid in beam tetrode
> > mode with fixed Eg2. The other input pentode operates as an inverting
> > anode follower with unity gain, but any THD generated in V1 is passed
> > on to be reproduced in V2. In effect, driver amp distortion is double
> > that of a single tube, and this defect also occurs in any amp using a
> > paraphase driver.
>
> I hadn't heard the term 'paraphase' until you mentioned it, so I did a
> bit of online research, found out that I've seen things like that before
> and I never liked it done 'that way', but yeah, using PENTODES just
> makes everything worse for distortion and potential imbalance. *Relying
> on the circuit gain characteristics of a tube for your design, or
> requiring a balance adjustment to make it work, is just silly. *As for
> me, I prefer the use of a pair of triodes as a direct coupled
> 'cathodyne' setup (careful biasing and component choices gives you
> pretty good results), though a 'long tail pair with a constant current
> on the cathodes' (something you had in one of your amps I think) would
> be a good alternative (some additional research suggests the latter
> might actually work better in an overdriven guitar amp). *The long tail
> pair has slight imbalance if you don't get close to a constant current
> on the cathode, so the simpler 'cathodyne' splitter gives you better
> balance with fewer parts (though it may require series resistors for
> downstream grids in case they draw current during overdrive on guitar amps).
>
> anyway, I found a couple of interesting web sites that describe the
> various types of phase splitters (among other things)

Quad-II used a kind of floating paraphase. Nobody much understands
exactly how it works but fact is that the output of one EF86 is
reduced
by resistance divider and fed to the grid of another EF86 and both
thus have a stage which effectively has 6dB of local positive FB. Both
EF86 have to make up to about 40Vrms for each KT66 grid, ( depending
on the load ). I've tried using KT88 in triode with fixed bias in Quad-
II with
an all triode input stage using low µ SE input and LTP driver with CCS
cathode tail. There is definately less high order HD products but the
measurements don't get dramatically better than the original Quad-II.
I've also tried using EF86 set up as a true LTP rather than paraphase
and methinks all things that I have tried are better measuring and
sounding than anything concocted for a quid by Peter Walker, ( God luv
'im ).
See http://www.turneraudio.com.au/quad2powerampmods.htm

GE published a book giving 17 amps from 5W to 1,100W and in it they
recommended both Williamson and paraphase circuits. The best paraphase
circuits are done using low µ triodes with a following balanced amp so
that the paraphasing is done at low signal levels where the positive
FB doesn't increase HD very much because it is so low to begin with.


> there's a general move to create something 'patentable' so that you have
> a portfolio of intellectual property, regardless of whether or not it is
> actually better. *But in cases where another guy's patent steps on your
> design, it might be necessary to go a slightly inferior route to avoid
> paying royalties. *By now all of those patents are expired.


Indeed.

Patrick Turner.

[Patrick Turner]

On May 21, 10:07*am, John Byrns > wrote:
> In article >,
> *Big Bad Bob > wrote:
>
> > On 05/20/11 03:22, Patrick Turner so wittily quipped:
> > > Baxandall's amp isn't real bad, but the first input pentode must
> > > produce a voltage large enough to drive one 6L6 grid in beam tetrode
> > > mode with fixed Eg2. The other input pentode operates as an inverting
> > > anode follower with unity gain, but any THD generated in V1 is passed
> > > on to be reproduced in V2. In effect, driver amp distortion is double
> > > that of a single tube, and this defect also occurs in any amp using a
> > > paraphase driver.
>
> > I hadn't heard the term 'paraphase' until you mentioned it, so I did a
> > bit of online research, found out that I've seen things like that before
> > and I never liked it done 'that way', but yeah, using PENTODES just
> > makes everything worse for distortion and potential imbalance. *Relying
> > on the circuit gain characteristics of a tube for your design, or
> > requiring a balance adjustment to make it work, is just silly.
>
> I prefer the floating paraphase phase inverter as it has many advantages over
> other forms of phase inverter. *If the inverter tube has sufficient gain,
> balance is excellent and no balance adjustment is necessary.

I've seen several versions of floating paraphase, usually you need to
have output tube grids biased at 0Vdc so that the feed from R divider
to one input tube grid is also at 0Vdc like the V1 tube. Using fixed
bias with adjust pots for the two output tubes complicates the design
unecessarily. But I've always found them slow, ie, their bandwidth is
lower than other methods so amp stabilization at HF for unconditional
stability even with a pure 0.22 uF load is more difficult to achieve,
so I never ever have used paraphase in any amp I've built. Many other
methods are better.

The best natural balance is achieved with a LTP in which the tubes on
each side do not need to be matched, and the drive to each OP tube is
dependant on the equality of the resistance loads on the two tubes of
the LTP. 1% metal film resistors have been routinely available for
many years now and they don't change value like the crappy old carbon
composition types.

Patrick Turner.

[Patrick Turner]

On May 21, 12:21*pm, flipper > wrote:
> On Fri, 20 May 2011 06:54:32 -0700, Big Bad Bob
>
>
>
>
>
> > wrote:
> >On 05/20/11 03:22, Patrick Turner so wittily quipped:
> >> Baxandall's amp isn't real bad, but the first input pentode must
> >> produce a voltage large enough to drive one 6L6 grid in beam tetrode
> >> mode with fixed Eg2. The other input pentode operates as an inverting
> >> anode follower with unity gain, but any THD generated in V1 is passed
> >> on to be reproduced in V2. In effect, driver amp distortion is double
> >> that of a single tube, and this defect also occurs in any amp using a
> >> paraphase driver.
>
> >I hadn't heard the term 'paraphase' until you mentioned it, so I did a
> >bit of online research, found out that I've seen things like that before
> >and I never liked it done 'that way', but yeah, using PENTODES just
> >makes everything worse for distortion and potential imbalance. *Relying
> >on the circuit gain characteristics of a tube for your design, or
> >requiring a balance adjustment to make it work, is just silly.
>
> Yes, well, the original Williamson called for a balance control on the
> separate triode voltage amps because their gain is what it is. The
> Williamson looks balanced but unless the triodes are identical, fat
> chance, it isn't. (He later decided GNFB was enough to not need the
> balance pot).

Williamson fell under the spell of the bean counters who had declared
war upon anyone who ever used one more resistor than necessary
acording to the rules laid down by the Society Of Bean Counters.

So he used that stupid arrangement with his KT66 cathode circuit
involving pots to balance ****. Balance it did, until a tube over
heated, and in EVERY single Williamson sample I have had to repair,
guess what - fried pots where thy just should *never ever* be used.
Leak's idea of cathode bias with two R&C bias networks was best, and
**** the rest. Its because the dual R gave the best bias regulation.

The balance of the Willy *short* tail pair, STP, was poor because the
tail R was such a low value. But the concertina as per Willy gave
excellent balance providing anode and cathode R were equal. This
balance is maintained well enough in a Willy amp, but can be be much
improved if a 4k7 is put in between 0V and the 470R which is in the
orriginal. THEN the natural balance of the STP becomes good enough to
never wish for more. But with that 4k7 added, the STP won't give very
good balance if driven on only one side, like the Leak circuit and so
many others, Mullard 520 etc. The simple answer to good balance and
simplicity is to use an LTP with CCS tail.

And if one don't like the 2H generated in V1 SE stage from ruining
music then use an input LTP with 6SN7/6CG7/6DJ8/ etc for V1 and V2,
with CCS tail, then use a second LTP for V3 and V4 with
6SN7/6CG7/12BH7/EL84/EL86/ etc, which has a tail R taken to -150Vdc.
The amp input is taken to V1 grid and GNFB is applied to V2 grid, and
the whole input-driver is thus beautifully balanced.
I recall I saw a version in RDH4, but have forgotten where, and it
don't matter because in 1955 they didn't have handy things like an
MJE340 which makes a splendid CCS.

> The Baxandall is a floating paraphase, which uses negative feedback.
>
> Look at it again. The second pentode is driven by the difference of
> the two signal paths, the two 470k summing 'sense' resistors, and is
> not operating open loop like the Williamson voltage amp triodes are.

True. What distracted me was that the SP61 have different anode RL for
Idc, input has 47k, and second tube has 4k7, and this looks like a
typo. Let's assume both SP61 have RLdc = 47k. But you'll find balance
only fair enough. The higher the gain of such signal pentodes, the
better the balance becomes. I don't like seeing any grid circuit
operating from a high impedance like the two 470k. Isn't the Baxandall
circuit almost identical to the Schmitt? p526 RDH4.

But ARC d40 used a circuit where the input signal came to one input
tube with cathode FB and also to a unity gain amp to make the second
phase which powered a second input tube with an oppositely phased FB
signal. The OPT had a CT and there were balanced GNFB loops of
opposite phase. Too complex of course. But the d40 was better IMHO
than later ARC which became a ****in nightmare of complexity.


> I used a similar floating paraphase on my "Batman" battery guitar amp
> but used triodes and since they were low gain I 'predisposed' the
> balance to nominal, and let the feedback work around that, but with
> pentodes you have lots of gain for NFB around the phase splitter.
>
> The floating paraphase has a different HF roll off on the two paths
> but, then, so does a concertina.

Also true, but the HF output roll off of the two phases in a
Williamson are both at such a high F that the THD thus generated is
well above 20kHz and not important. I found that the the HF balance
from a concertina could be made near equal if about 15pF or other low
C value is across the cathode R of the concertina to slightly boost
the gain from the anode.
>
> None of them are 'perfect'.

In RDH4, P344, there is a 30W beam tetrode amp with 807 with SE
pentode input, pentode concertina.
Page 344 has the triode Williamson with 807. P353 is interesting
though, positive and negative FB loops are used. This is PURE
QUIRKINESS for those who must have quirks in their amplifier
collection. I have never seen any commercial design with PFB and NFB -
too hard to get right. But most amps do have quite a few quarks
lurking about.

Nothing is ever perfect.

Patrick Turner.

[Patrick Turner]

On May 21, 7:03*pm, Big Bad Bob <BigBadBob-at-mrp3-
> wrote:
> On 05/20/11 19:21, flipper so wittily quipped:
>
>
>
>
>
> > On Fri, 20 May 2011 06:54:32 -0700, Big Bad Bob
> > > *wrote:
>
> >> On 05/20/11 03:22, Patrick Turner so wittily quipped:
> >>> Baxandall's amp isn't real bad, but the first input pentode must
> >>> produce a voltage large enough to drive one 6L6 grid in beam tetrode
> >>> mode with fixed Eg2. The other input pentode operates as an inverting
> >>> anode follower with unity gain, but any THD generated in V1 is passed
> >>> on to be reproduced in V2. In effect, driver amp distortion is double
> >>> that of a single tube, and this defect also occurs in any amp using a
> >>> paraphase driver.
>
> >> I hadn't heard the term 'paraphase' until you mentioned it, so I did a
> >> bit of online research, found out that I've seen things like that before
> >> and I never liked it done 'that way', but yeah, using PENTODES just
> >> makes everything worse for distortion and potential imbalance. *Relying
> >> on the circuit gain characteristics of a tube for your design, or
> >> requiring a balance adjustment to make it work, is just silly.
>
> > Yes, well, the original Williamson called for a balance control on the
> > separate triode voltage amps because their gain is what it is. The
> > Williamson looks balanced but unless the triodes are identical, fat
> > chance, it isn't. (He later decided GNFB was enough to not need the
> > balance pot).
>
> > The Baxandall is a floating paraphase, which uses negative feedback.
>
> > Look at it again. The second pentode is driven by the difference of
> > the two signal paths, the two 470k summing 'sense' resistors, and is
> > not operating open loop like the Williamson voltage amp triodes are.
> > I used a similar floating paraphase on my "Batman" battery guitar amp
> > but used triodes and since they were low gain I 'predisposed' the
> > balance to nominal, and let the feedback work around that, but with
> > pentodes you have lots of gain for NFB around the phase splitter.
>
> curious, which of these designs gives you the best overall gain,
> transient response, overdrive characteristics, and lowest cost (or 'part
> count')? *Down side for cathodyne is that you have to make sure that the
> Rp-Rk never drops below around 50V or so (depending on the tube) in the
> worst case voltage swing. *Alternative is to put a 2nd set of triodes
> between the splitter and the output tubes, but not sure if that adds
> potential imbalance or not (you'd have to match more parts again). *At
> that point I'd do the 'long tail' thing and match the Rp's, and use a
> constant current source.- Hide quoted text -
>
> - Show quoted text -

My website shows numerous schematics which speak volumes about my
preferences for best-ness.

But in the last few years I have re-engineered a few high end amps
including ARC VT100, Manley Labs Snappers, and an old pair of Dynaco
Mk-VI.

In these amps there were 4 x 9 pin sockets for each channel so to make
good use of the sockets. With the ARC VT100, I did the following....

I stripped out nearly all of what ARC used, leaving only about 5% of
basic heater circuits and PSU. A carpenter's chisel was used remove
the tracks and surplus stuff to the bin. There's a lotta stuff which
does not give more hi-fi, so its best removed.. New tracks were used
using links of wire. 101 other things were don, like soldering copper
wire to bases of 6550 to be able to wire them in so they can't fall
out of the terrible octal sockets ARC have used which have very poor
grip on tube pins.

Then,

Input = LTP with a one twin triode 6DJ8 on each side. MJE340 CCS
cathode tail to a negative rail.

Driver = 2 x 12BH7, one on each side of balanced amp with common Rk to
negative rail. Balance drive was better than 1%.

Output tubes all fitted with individually adjustable fixed bias and bi
colour green/red LED used to indicate bias condition of tubes and with
full protection against bias failures. The original ARC had a total of
5 TO92 tiny j-fets used as CCS, but they are all unsuitable fragile
and unecessary. Just why Big Boys like ARC don't include such things I
routinely do is beyond my comprehension.

I did a similar thing on Dynaco mk-V1 but with EL84 in triode used on
each side of driving balanced amp.

Patrick Turner.

[John L Stewart]

In RDH4, P344, there is a 30W beam tetrode amp with 807 with SE
pentode input, pentode concertina.
Page 344 has the triode Williamson with 807. P353 is interesting
though, positive and negative FB loops are used. This is PURE
QUIRKINESS for those who must have quirks in their amplifier
collection. I have never seen any commercial design with PFB and NFB -
too hard to get right. But most amps do have quite a few quarks
lurking about.

Nothing is ever perfect.

Patrick Turner.[/QUOTE]

That 807 amp on p344 is simply a barely passable PA type, nothing more. The NFB connexion used makes the OP stage more susceptable to PS ripple.

The amp shown on p353 was probably never available commercially, but the text gives a good description of how the circuit works.

Several of the Electrovoice Circlotrons used +ve current FB from the secondary of the OPT to accomplish very low to zero internal impedance & go even negative. Another way of looking at it is infinite or -ve DF.

If we looked a bit we could probably find others. But not something for an amatuer to attack.

Makes up for speaker lead resistance. And something no one seems to talk about, that being the DC resistance of the speaker coil itself.

Cheers to all, John

[Patrick Turner]

On May 22, 9:47*am, John L Stewart <John.L.Stewart.
> wrote:
> In RDH4, P344, there is a 30W beam tetrode amp with 807 with SE
> pentode input, pentode concertina.
> Page 344 has the triode Williamson with 807. P353 is interesting
> though, positive and negative FB loops are used. This is PURE
> QUIRKINESS for those who must have quirks in their amplifier
> collection. I have never seen any commercial design with PFB and NFB -
> too hard to get right. But most amps do have quite a few quarks
> lurking about.
>
> Nothing is ever perfect.
>
> Patrick Turner.
>
> That 807 amp on p344 is simply a barely passable PA type, nothing more.
> The NFB connexion used makes the OP stage more susceptable to PS ripple.

Agreed. I like the RDH4 book, its like a bible, but the wisdom needs
to be applied in a modern world.
>
> The amp shown on p353 was probably never available commercially, but the
> text gives a good description of how the circuit works.

Indeed.
>
> Several of the Electrovoice Circlotrons used +ve current FB from the
> secondary of the OPT to accomplish very low to zero internal impedance &
> go even negative. Another way of looking at it is infinite or -ve DF.

Bogan also did variable damping factor with positive current FB. I've
tried it. Dagerous, because Vo rises when RL is reduced, and if the
load is a short the damn thing tries to oscillate to death. Not nice.
But the PCFB can be made to work at LF only which then vastly improves
the bass "tighness", whatever that is. Such things are gimics. The
PCFB increases THD/IMD and reduces BW.
>
> If we looked a bit we could probably find others. But not something for an
> amatuer to attack.

Depends. 1% of amateurs know more than many professionals. Pros only
know so much, and bean counters limit realization of many ideas.
>
> Makes up for speaker lead resistance. And something no one seems to talk
> about, that being the DC resistance of the speaker coil itself.

Theil and Small had a lot to say about speakers; A few lines of
incomprehensible text, then a formula stretching across the page,
then another bit of text, then another formula.

They would lecture everyone about speakers et all and at the end of
any lecture there remained a stubborn palpable presence of the non
diminished mysteries of how speakers worked.

Anyway, about 40 years later, a few blokes who understood a little of
the math were able to cobble up a program or three so that other
blokes just could dial in a speaker driver characteristics, go CLICK,
and there was the best kinda box needed without the trial and errors
involved with guesswork which always produces expensive samples of
firewood. Somehere buried in the input data was the winding
resistance. With other books and info stuff a bloke then could learn
how to make most dynamic speakers look like a humble resistance as far
as eyes of an amplifier were concerned. You liddle beauty, because
then the damn crossovers would work as intended. But then a good
speaker maker needs to build around the measured and non flat
frequency response of the selected drivers, and if you've ever build a
4 way speaker, bass, lower MF, uper MF, and HF, and all with second
order filters, boy, what a lot to get right! - many, many, many tings
and tings.

The world is chokka block full of both amateurs and pros who for 101
reasons never consider enough factoids, and most won't admit it.


Patrick Turner.


>
> Cheers to all, John
>
> --
> John L Stewart

[Big Bad Bob]

On 05/21/11 22:03, flipper so wittily quipped:
> I'm not really a 'fan' of the paraphase but the battery filament tubes
> I was using in Batman didn't leave much choice. The pentode-triode
> (and diode I'm not using) share the same filament in the 1D8GT and
> that ruled out anything under the 'cathodes'.

ugh, yeah probably no choice. even a long tail wouldn't work well
unless you can somehow CCS both the filament AND Ik at the same time
[unlikely]. So definitely limited in what's possible.

the basic circuit design is kind of like the way a differential
amplifier circuit works, where the sum of the inverting + non-inverting
must become zero when the circuit is in balance. The error is then
infinitely amplified, and NFB re-balances everything to create a
reliably amplified signal (or that's the theory). So when the output of
the 'thing' that produces the inverting signal is summed with the
original, this creates the 'error' signal. Ideally, you have zero error
when the circuit works. Unfortunately, low gain triodes will result in
higher error, so you'll probably need something to adjust balance on it.
Hence... (your additional comments)

> I call mine a 'hybrid' paraphase because, as mentioned, the triodes
> don't have a lot of gain so it starts off looking like a plain
> paraphase where you tap a 'small' signal off the first phase to drive
> the second. But rather than just a tap I also link the second phase
> into it, like a floating paraphase, so the tap 'predisposes' the
> signal level and the feedback works around that predisposition.

I'm guessing this corrects for what I mentioned above. 'Tricky' stuff.

> If the tubes are identical and exactly as spec'd for bogey then
> everything gains and sums up to what's expected so there's,
> essentially, 'nothing for the feedback to do'. But if either are off
> then the summation doesn't 'come out right' and tends to push the
> second triode toward a match.

and that's another problem with paraphase - you need matching 'things'
and component aging isn't compensated for in the least.

> It isn't very much NFB, maybe 9 dB, but, hey, why not? Actually, I'm
> not quite sure how to calculate it but there's a 3 to 1 voltage
> difference with R2 connected there ('closed loop') vs not so I figure
> that's 9.5dB.

> http://flipperhome.dyndns.org/Batman.htm

pretty cool. FYI something LIKE THIS is ideal for generating "tube amp
distortion" without wasting a lot of power. You could use an 8 ohm
dummy load and overdrive it into a different amp (which then gets you
the volume). /me getting ideas.

> The amp is still dominated by 2's harmonics but that's from the open
> ended first stage.

a tetrode? Ok, just watch out for the reverse-resistance range at low
current. 100k on the plate may suggest that you're already in that
slot, hence the 2nd harmonic distortion [which may get even worse]. You
might halve that and adjust bias for twice the current. OK gain may be
lower, or then again may not. You're probably dropping 40v or so across
the 100k which is .4 ma so 47k and .8 ma should get you a bit more
linearity. . Ep too
low is also likely to create problems. My rule is to pick a voltage
that's about 1/2 B+ for the 'rest state', using a plate current that's
reasonably linear for an easily obtainable G1 bias. Anyway, if you can
put in test signals you might want to do that to generate your own
curves, maybe 3VDC with a potentiometer and manual readings (or storage
scope if you have one). /me reminded of the $89 pocket scope I bought a
few months ago - very nice, goes up to 1Mhz.
[i]
>> Down side for cathodyne is that you have to make sure that the
>> Rp-Rk never drops below around 50V or so (depending on the tube) in the
>> worst case voltage swing.

yes. using high B+ helps. If you've got power tubes that need >400V
that's not too difficult. You can add an R+C filter, drop down to maybe
380V with a relatively large R and make that the supply for the
cathodyne part. I like to split the voltage so that the G1 bias is less
than the voltage drop across Rp or Rk at steady state, and is also
SIGNIFICANTLY less than 1/5 of the supply voltage. So then the best
case voltages for 60V negative bias (on the power tubes) would be 70V on
the cathode and ~310V on the plate (steady state, B+ 380), with 130 on
the cathode and 240 on the plate at the 'highest current' point.
Unfortunately this will have higher 2nd harmonic distortion due to the
wider current swing. Anyway, Rp - Rk is 110, which is more than enough,
so this could be tweeked a bit more, maybe 90V on the cathode and 290 on
the plate at steady state, then Rp - Rk is 80V, still well within the
linear range for a typical triode. Then you just pick resistors that
match your desired current, and make sure the G1 volts at steady state
is around Ek + bias. But if this is directly driven from a prior stage
then you must increase Ek to an even higher amount to prevent Ep on the
driving stage from getting too low. So now you tweek it up a bit more,
with steady state Ek at 110 (~50V min on driver tube plate), and 280V
Ep, with 'worst case' at 170V Ek and 220V Ep (now down to 50V), and
you're "there". Current only has to change by a fraction of the
quiescent value, you can direct drive it from the prior stage, and if
you choose the right parts (and maybe even regulate the B+ for the
pre-amps) it self-balances. Anyway, point well taken on min Ep - Ek.

>> At that point I'd do the 'long tail' thing and match the Rp's, and
>> use a constant current source.
>
> Neither Williamson nor Baxandall had transistors to conveniently
> create a CCS.

you could do it with tubes. Ground grid, put Rk that sets the current
to what you want, plate in series with long tail cathodes, and use a
voltage divider (filtered) to bias the grids. But then Ek is much
higher than it would be with a transistor, since you could drop down
below 2v and still get your CCS (thereby using ground potential for the
grid bias). Cheating and using germanium transistors you could go even
lower.

> It also depends on whether it matters enough to bother with. PP gain
> imbalance manifests predominately as 2'nd harmonic and, remember,
> that's 'the first to go' with NFB.

interesting point. yeah, you can tolerate a bit of imbalance. But the
result is likely to be a reduction in output power, or uneven clipping
when overdriven.

[Big Bad Bob]

On 05/21/11 04:41, Patrick Turner so wittily quipped:
> Williamson fell under the spell of the bean counters who had declared
> war upon anyone who ever used one more resistor than necessary
> acording to the rules laid down by the Society Of Bean Counters.

that can happen. accountants driving design. sometimes good, sometimes
not. 'cost reduction' phases are typical.

> So he used that stupid arrangement with his KT66 cathode circuit
> involving pots to balance ****. Balance it did, until a tube over
> heated, and in EVERY single Williamson sample I have had to repair,
> guess what - fried pots where thy just should *never ever* be used.
> Leak's idea of cathode bias with two R&C bias networks was best, and
> **** the rest. Its because the dual R gave the best bias regulation.

self-correcting (inherently stable) circuit designs. who'd a thunk it.
That as opposed to potentially UNstable ones. Like that one.
Assuming nothing ever overloads/overheats, nothing ever ages, nothing
ever works differently than it does in the design lab, etc. is just a
recipe for RMA's and costly design revs. And unhappy customers.

it's my opinion that adjustments are bad, anyway. It's an extra step
during the assembly that requires a technician to perform. Adding a few
extra parts to PREVENT that step is preferable, my $.10 worth anyway.

[John Byrns]

In article >,
Patrick Turner > wrote:

>
> In RDH4, P344, there is a 30W beam tetrode amp with 807 with SE
> pentode input, pentode concertina.
> Page 344 has the triode Williamson with 807. P353 is interesting
> though, positive and negative FB loops are used. This is PURE
> QUIRKINESS for those who must have quirks in their amplifier
> collection. I have never seen any commercial design with PFB and NFB -
> too hard to get right. But most amps do have quite a few quarks
> lurking about.

Look here for a common combined PFB & NFB circuit.

http://www.triodeel.com/dynast35.gif

--
Regards,

John Byrns

Surf my web pages at, http://fmamradios.com/

[John Byrns]

In article >,
Patrick Turner > wrote:

>
> Quad-II used a kind of floating paraphase. Nobody much understands
> exactly how it works but fact is that the output of one EF86 is
> reduced
> by resistance divider and fed to the grid of another EF86 and both
> thus have a stage which effectively has 6dB of local positive FB. Both
> EF86 have to make up to about 40Vrms for each KT66 grid, ( depending
> on the load ).

It's not really that hard to figure out how it works, a lot of the quirkiness is
due to the acrobatics needed to apply negative feedback to the common cathode of
the voltage amplifier and phase splitter. This was probably a bean counter
thing to eliminate a couple of electrolytic capacitors.

--
Regards,

John Byrns

Surf my web pages at, http://fmamradios.com/

[Patrick Turner]

Somebody said...

> > Neither Williamson nor Baxandall had transistors to conveniently
> > create a CCS.
>
> you could do it with tubes. *Ground grid, put Rk that sets the current
> to what you want, plate in series with long tail cathodes, and use a
> voltage divider (filtered) to bias the grids. *But then Ek is much
> higher than it would be with a transistor, since you could drop down
> below 2v and still get your CCS (thereby using ground potential for the
> grid bias). *Cheating and using germanium transistors you could go even
> lower.

Easiest 10mA CCS for an LTP is with a 6AU6 pentode. Anode to the
common LTP cathodes, screen bypassed to cathode, fixed Eg1 bias at
-100V, fixed cathode supply at -150V with Rk at about 5k2, so that if
the 6AU6 µ is say 1,600, effective Ra = 8.7Meg. But with an MJE340,
you get much more than that easily. Tube CCS really need two tubes in
series to get really high finite Ra values, and bean counters in 1955
had firmly forbiden any such extravagances in consumer grade audio
gear. "Cracked carbon" resistors with accurate and stable R values
were also expensive and forbidden. But making do with sub-optimal
solutions was very popular.

Patrick Turner.

[GRe]

"John Byrns" > wrote in message
...
> In article
> >,
> Patrick Turner > wrote:
>
>>
>> In RDH4, P344, there is a 30W beam tetrode amp with 807 with SE
>> pentode input, pentode concertina.
>> Page 344 has the triode Williamson with 807. P353 is interesting
>> though, positive and negative FB loops are used. This is PURE
>> QUIRKINESS for those who must have quirks in their amplifier
>> collection. I have never seen any commercial design with PFB and NFB -
>> too hard to get right. But most amps do have quite a few quarks
>> lurking about.
>
> Look here for a common combined PFB & NFB circuit.
>
> http://www.triodeel.com/dynast35.gif


6.3VAC on the 6BQ5 (common) cathodes????

Gio


>
> --
> Regards,
>
> John Byrns
>
> Surf my web pages at, http://fmamradios.com/

[Big Bad Bob]

On 05/22/11 04:40, flipper so wittily quipped:
> On Sun, 22 May 2011 03:49:29 -0700, Big Bad Bob
> > wrote:
>
>> On 05/21/11 22:03, flipper so wittily quipped:
>>> I'm not really a 'fan' of the paraphase but the battery filament tubes
>>> I was using in Batman didn't leave much choice. The pentode-triode
>>> (and diode I'm not using) share the same filament in the 1D8GT and
>>> that ruled out anything under the 'cathodes'.
>>
>> ugh, yeah probably no choice. even a long tail wouldn't work well
>> unless you can somehow CCS both the filament AND Ik at the same time
>> [unlikely]. So definitely limited in what's possible.
>
> Filament IS Ik. And when more than one tube in the bottle it's the
> combined Ik from all of them. No kind of 'tail' will work.

yeah, ok. technically Ik would be the sum of Ip + Ig (the latter
irrelevant for triodes) but ok. Filament current is really a different
path and that's what I meant. So in your case "Ik" = Ip + filament
current (whatever Ix that would be). That's just a distraction, anyway.
However, if you _did_ have a way of isolating the actual cathode
EMISSION current from the filament current you might be able to get it
to work. /me can't think of any way to do that, though.

> I could have used single triodes but it still isn't so easy to power
> the filaments since they're the 'cathode' and would be floating on the
> 'tail'. Gets to be a real mess.

and that's the point.

[John L Stewart]

Before this thread went off the rails did anyone mention that McIntosh uses a seperate winding on the OPT for overall NFB?

Cheers, John

[Patrick Turner]

I mentioned......
> > I have never seen any commercial design with PFB and NFB -
>
> Of course you have and I gave you examples the last time you said the
> same thing.

I've been saying the same thing because I've never seen PFB used in
commercial amps like the way its done in RDH4 at that amp. Sometimes
bootstrapping is PFB, but usually the gain increase is mild, from gain
with a load to gain which approaches µ. However, come to think about
it, Dynaco bootstrapped the pentode input tube anode RL ahead of the
triode concertina to boost the gain of the pentode. The gain with
bootstrapping a pentode often rises much more than with a triode tube
because the pentode has its anode feedback screened off from the
electron stream. Pentode µ is gm x Ra, and as pentode Ra is so high
then µ is high.
>
BTW,
I have to repair the design results of acountants and bean counters
all too often.


Patrick Turner.

[Patrick Turner]

On May 23, 5:33*am, John Byrns > wrote:
> In article >,
> *Patrick Turner > wrote:
>
>
>
> > In RDH4, P344, there is a 30W beam tetrode amp with 807 with SE
> > pentode input, pentode concertina.
> > Page 344 has the triode Williamson with 807. P353 is interesting
> > though, positive and negative FB loops are used. This is PURE
> > QUIRKINESS for those who must have quirks in their amplifier
> > collection. I have never seen any commercial design with PFB and NFB -
> > too hard to get right. But most amps do have quite a few quarks
> > lurking about.
>
> Look here for a common combined PFB & NFB circuit.
>
> http://www.triodeel.com/dynast35.gif
>
> --
> Regards,
>
> John Byrns
>
> Surf my web pages at, *http://fmamradios.com/

Indeed, PFB cathode to cathode of the input stages and in the presence
of NFB. But how much PFB is there? What effect would it have on
stability margins and reactive ( capacitance) load tolerance? I've
always seen PFB as one step forward, 2 steps backward - a cheap nasty
fix if ever there was one!

Patrick Turner.

[Patrick Turner]

On May 23, 5:38*am, John Byrns > wrote:
> In article >,
> *Patrick Turner > wrote:
>
>
>
> > Quad-II used a kind of floating paraphase. Nobody much understands
> > exactly how it works but fact is that the output of one EF86 is
> > reduced
> > by resistance divider and fed to the grid of another EF86 and both
> > thus have a stage which effectively has 6dB of local positive FB. Both
> > EF86 have to make up to about 40Vrms for each KT66 grid, ( depending
> > on the load ).
>
> It's not really that hard to figure out how it works, a lot of the quirkiness is
> due to the acrobatics needed to apply negative feedback to the common cathode of
> the voltage amplifier and phase splitter. *This was probably a bean counter
> thing to eliminate a couple of electrolytic capacitors.

The solution to the problem of low open loop gain suited bean counters
at Quad. But if you make the two EF86 behave as a real LTP with common
cathode R to -400Vdc, or a CCS, and without the mild 6dB PFB boost of
the paraphase inverter principle used, then the differential gain is
halved and if the same amount of NFB was applied globally, you'd need
2.8Vrms for clipping power instead of only 1.4Vrms. One solution is to
use 6BX6 as input tubes with Ia in each at nearly 2mA and then the gm
rises well above what it is in EF86 and by carefully juggling the load
values and biasing R to OP tubes which would better be EL34 with more
gain than KT66, then you get increased open loop gain without the
paraphase connection and better stability etc, and the input pair may
be set up as a true LTP.

I've also used KT88 and KT90 in Quad-II.

Sure anyone may work out ther Quad circuit workings. But I've rarely
ever met that anyone.

Patrick Turner.
>
> --
> Regards,
>
> John Byrns
>
> Surf my web pages at, *http://fmamradios.com/

[Patrick Turner]

On May 26, 7:35*pm, flipper > wrote:
> On Thu, 26 May 2011 00:37:17 -0700 (PDT), Patrick Turner
>
> > wrote:
> >I mentioned......
> >> > I have never seen any commercial design with PFB and NFB -
>
> >> Of course you have and I gave you examples the last time you said the
> >> same thing.
>
> >I've been saying the same thing because I've never seen PFB used in
> >commercial amps like the way its done in RDH4 at that amp.
>
> Now you've changed it again by adding "like the way."
>
> > Sometimes
> >bootstrapping is PFB, but usually the gain increase is mild, from gain
> >with a load to gain which approaches µ. However, come to think about
> >it, Dynaco bootstrapped the pentode input tube anode RL ahead of the
> >triode concertina to boost the gain of the pentode.
>
> Told ya so.
>
> The Harmon Kardon 'Trio' also uses PFB and is the basic topology I've
> used in at least three of mine.
>
> > The gain with
> >bootstrapping a pentode often rises much more than with a triode tube
> >because the pentode has its anode feedback screened off from the
> >electron stream. Pentode µ is gm x Ra, and as pentode Ra is so high
> >then µ is high.
>
> >BTW,
> >I have to repair the design results of acountants and bean counters
> >all too often.
>
> You've never had to do it even once because bean counters don't do
> design. Never have, don't now, and never will.

IMHO, you are not quite correct because bean counters and accountants
do considerable design work during development of any product. You may
laugh, but bean counters and accountants are employed to "just say no"
to engineers' first, second and third attempts to design a prototype.
This is the standard method of Bean Counter Design Process, BCDP.
Often engineers are not even employed at all lest they cost money and
crerate arguments and waste everyone's time around the office. But if
engineers are employed, design might be complete after attempt No 4,
when finally the parts count and complexity, size, and weight and
strength have been reduced to a horrible minimum to get the product to
barely make it past the warranty and its defects ensure it will never
be collectable or a classic design or any kind of sample of goodness.
The manufacture of many many products is put through the same old dumb
down mill run by the bean counters. Bean counters also ensure that
minimum or even zero product development ever takes place; what is
simulated once during 2 hours on a PC becomes the product sold to the
public, and R&D really becomes "Run and Duck" the irate buyers of a
product which fails before the warranty period expires. The Quad-II
Forty made in China is a very good example of Applied Crapology By
Bean Counters, or ACBBC, where every effort has been avoided to make a
good product while disguising what has been made with a chic paint job
which does not improve the sound by even +0.002 dB.

The Product Promoters ensure the quality removal design work by bean
counters will yield nice fat company profits for shareholders who have
a nasty habit of selling their shares in a panic if the fatness isn't
fat enough, because they are into fatness maximums.
But then the company in China might be "owned" by a relative of a high
ranking member of China's elitist Communist Party and profits are
REALLY FAT because the Quad amps are sold high while workers maybe
only earn 64c per hour. People can be persuaded to eat a **** sandwich
very easily, and big profits have been made throughout history selling
**** which has been diluted before being applied between very thin
slices of bread made from nutrition free white flour with chemical
additives cheaper than providing decent bread. So you can't even get a
good **** sandwich if you wanted one; even this product has been
Designed Down to maximise profits.

We are seeing Chinese made cars in shops here for 10 grand drive away
price. They fail crash tests dismally, and maybe you need to buy two
to ensure you have a spare during next years's breakdowns, but hey,
its better than a bicycle.

I hate shopping and travel. If I shop, its mostly junk I have to buy,
and if I travel, the people at arrival line up to empty my wallet, and
there's nothing to show for it except an empty wallet. Lots of things
in life are shambolic, devoid of any authenticity or wonderment. I
like bicycles.

I don't like Big Tobbacco, Big Hudrocarbon, or Big Brother and a whole
big list of other Mr Bigs in manufacturing who perpetuate products I
don't have any desire for. They all want me to be a debt ridden but
addicted and compliant little consumer. But I say no to most of them.
They deal in negativity, so from me they get negativity.

Patrick Turner.




>
>
>
>
> >Patrick Turner.- Hide quoted text -
>
> - Show quoted text -

[John Byrns]

In article >,
Patrick Turner > wrote:

> On May 23, 5:38*am, John Byrns > wrote:
> > In article
> > >,
> > *Patrick Turner > wrote:
> >
> >
> >
> > > Quad-II used a kind of floating paraphase. Nobody much understands
> > > exactly how it works but fact is that the output of one EF86 is
> > > reduced
> > > by resistance divider and fed to the grid of another EF86 and both
> > > thus have a stage which effectively has 6dB of local positive FB. Both
> > > EF86 have to make up to about 40Vrms for each KT66 grid, ( depending
> > > on the load ).
> >
> > It's not really that hard to figure out how it works, a lot of the
> > quirkiness is
> > due to the acrobatics needed to apply negative feedback to the common
> > cathode of
> > the voltage amplifier and phase splitter. *This was probably a bean counter
> > thing to eliminate a couple of electrolytic capacitors.
>
> The solution to the problem of low open loop gain suited bean counters
> at Quad. But if you make the two EF86 behave as a real LTP with common
> cathode R to -400Vdc, or a CCS, and without the mild 6dB PFB boost of
> the paraphase inverter principle used, then the differential gain is
> halved and if the same amount of NFB was applied globally, you'd need
> 2.8Vrms for clipping power instead of only 1.4Vrms.

You keep talking about "the mild 6dB PFB boost of the paraphase inverter
principle". I don't understand where you are getting this 6 dB boost? The
floating paraphase has the same gain as the concertina phase inverter, how does
the concertina equal the gain of the floating paraphse without PFB, or does the
concertina also use PFB? In any case only one out of the many many possible
variations of the floating paraphse could be said to incorporate PFB. I'm not
an expert on the LTP, and am not a big fan of it, I suspect that the truth here
is that the LTP throws away 6 dB of gain relative to the concertina and floating
paraphase.

--
Regards,

John Byrns

Surf my web pages at, http://fmamradios.com/

[Patrick Turner]

On May 27, 10:47*am, John Byrns > wrote:
> In article >,
> *Patrick Turner > wrote:
>
>
>
>
>
> > On May 23, 5:38*am, John Byrns > wrote:
> > > In article
> > > >,
> > > *Patrick Turner > wrote:
>
> > > > Quad-II used a kind of floating paraphase. Nobody much understands
> > > > exactly how it works but fact is that the output of one EF86 is
> > > > reduced
> > > > by resistance divider and fed to the grid of another EF86 and both
> > > > thus have a stage which effectively has 6dB of local positive FB. Both
> > > > EF86 have to make up to about 40Vrms for each KT66 grid, ( depending
> > > > on the load ).
>
> > > It's not really that hard to figure out how it works, a lot of the
> > > quirkiness is
> > > due to the acrobatics needed to apply negative feedback to the common
> > > cathode of
> > > the voltage amplifier and phase splitter. *This was probably a bean counter
> > > thing to eliminate a couple of electrolytic capacitors.
>
> > The solution to the problem of low open loop gain suited bean counters
> > at Quad. But if you make the two EF86 behave as a real LTP with common
> > cathode R to -400Vdc, or a CCS, and without the mild 6dB PFB boost of
> > the paraphase inverter principle used, then the differential gain is
> > halved and if the same amount of NFB was applied globally, you'd need
> > 2.8Vrms for clipping power instead of only 1.4Vrms.
>
> You keep talking about "the mild 6dB PFB boost of the paraphase inverter
> principle". *I don't understand where you are getting this 6 dB boost? *The
> floating paraphase has the same gain as the concertina phase inverter, how does
> the concertina equal the gain of the floating paraphse without PFB, or does the
> concertina also use PFB? *In any case only one out of the many many possible
> variations of the floating paraphse could be said to incorporate PFB. *I'm not
> an expert on the LTP, and am not a big fan of it, I suspect that the truth here
> is that the LTP throws away 6 dB of gain relative to the concertina and floating
> paraphase.

With any pair if paraphase input tubes with or without the "floating"
drive for V2 grid, there is 6dB PFB because you are using a fraction
of the output from V1 to drive V2. So say tou have a V1 and V2 input
parphase pair = 6SN7. Each may havea gain = 17, so that from V1 you
get -17Vo for a +1V input Vgk. The -17Vo V1 output signal is divided
down to -1Vgk and applied to V2 grid, and the % distortion created by
V1 is also created in V2, so that distortion is inceased in its
percentage V2 duely creates its expected +17Vo, and so for only 1Vin
at V1, you get a total of 34Vo from the two tubes at higher THD %.
This is certainly true of Quad-II and its feeble use of EF86. I've
measured it all. Now if the pair of 6SN7 triodes are set up as an LTP
with one grid taken to 0V, then to get 34Vo you need to apply 2V in,
and you might say gain is halved because you need 2Vi to get 17Vo from
each anode. Such an LTP is a form of one common cathode gain tube
driving a grounded grid tube, but there is no added gain by means of
PFB, and if the tail is a high R value, there is excellent even order
H reduction from balanced operation. Try doing some measurements.

The concertina "throws away" most of its gain so that +19Vin to a 6SN7
produces -17Va and +17Vk, with the +2Vgk needed to make the total
34Vak output, so open loop gain = 17, but closed loop gain is 34 / 19
= 1.79, and this has beautiful low THD because the 19dB current NFB
present.

The paraphase works OK if the input pair have only to make a low
voltage output less than 2Vrms to drive a balanced amp gain stage,
say a second 6SN7 LTP, which works best with a high resistance tail R,
or CCS. If the balanced driver amp has balanced drive to each of its
grids, the the cathode signal should only have distortion signal
present, while each triode of the pair produces gain of 17.

Input topologies used by many makers and designers "who didn't design
for mass production" as someone else ruefully explained, are
determined by need to gain fair input sensitivity while also being
able to sustain 20dB reduction of OLG by applied GNFB. Hence
Williamson's triode amp needed 2Vrms input for 16 Watts in triode from
KT66. Of course UL connection gave 32 Watts and sensitivity was
doubled if expressed as Watts per input volt. If instead of
Williamson's SET input stage and concertina with 19dB NCFB, you use a
paraphase with no NFB but with PFB, then input sensitivity is
doubled.

It so happens that a pair of cascaded 6SN7 triodes might have gain of
17, but typically its 15 in old amps because makers were loathe to run
driver tubes with more than 2mA. So gm is low and Ra is high and gain
= 15. Two stages got OLG = 225. But the use of EF86 became
irresistable to makers because accountants and bean counters said you
only needed 2 little compact EF86 to do what 4 triodes in 2 bulky
octal 6SN7 could do. Just how well the devices did things was never of
much concern. But it was amoung those few who liked the best technical
performance in terms of OL THD and bandwidth. The Williamson input/
driver stage ****s all over a pair of EF86 trying to make +/- 30Vrms
drive to a pair of OP tubes. But EF86 and the accountants prevailed.
Mullard went to EF86 plus a 12AX7 LTP, and yes, only two nine pin
sockets, and yes, loads more OLG, so Vin with 20dB global NFB was
0.2Vrms, so therefore the preamp could have -20dB of gain and maybe
one whole tube could be removed out of production. Preamps typically
could have one EF86 for a magnetic MM phono cart, followed by another
EF86 which wore "all the hats" possible including unity gain Baxandall
tone control, and ande follower buffereing of any input signals before
the power amp. A typical 1960 UL Mullard concoction producing 1/2 a
watt to a sensitive 16 ohm speaker of the day would fill a house with
sound, and produce bugger all THD. I would say the Williamson triode
amp with all triode input tubes and more of them might sound better,
and it to would have "bugger all THD", ie, less than 0.02% at normal
civilised listening levels. The Willy amp gave the best SNR.

I have used 6BX6 in Quad-II amps set up as a true LTP with CCS cathode
R and THD is much less than if one tries the same tubes in paraphase.
In Quad-II, the GNFB is applied in an unusual way to maintain
paraphase operation while being able to apply the GNFB. But if ever
there is a bodge in circuits, here it is! If the input pair is set up
as a true LTP, sensitivity is halved, and if the same *amount* of GNFB
is used, ie, about 10dB, then Vin needed for clipping is doubled,
using the same EF86 operating conditions as for the original Quad-II
amps. With 6BX6 / EF80, or even 6EJ7 / EF184, higher gm and higher OLG
is possible at at the same or lower OLG as EF86 and with higher
current to counter Miller C. Anyway, the last Quad-II upgrade I did
used 6BX6 plus KT88 which cope better with appalling inability of Quad-
II to get a good load match to any RL below 8 ohms. In about 1999, I
used SET tube = 12AT7 paralleled and driving 12AU7 LTP for trioded
KT88 with fixed bias for a very nice 20W class AB1 in triode - to me
it sounded better than original Quad-II. See the schematic at the
bottom of the page at http://www.turneraudio.com.au/quad2powerampmods.htm

So Quad always could have used 4 triodes for its input -driver stage.
So why didn't they do it? Probably because some stinking rotten small
minded parsimonious accountant or bean counter said "Peter, if we use
an extra 2 resistors in the Quad-II, we won't be able to buy the
latest Morris Major this year..." While Mullard might have been
saying "Peter, we have terrific deals on EF86..."

Meanwhile, trying to manufacture anything in the UK after WW2 was
difficult. All the best guys had been killed in WW2, and copper and
iron was scarce. Unions wanted bucket fulls of cash for very little
work. OK, make miniature OPTs. Smaller things cost less to make . The
missus was always pregnant with baby boomer kids. So how to get ppl to
buy Quad? get the price down, get the hype up, and don't sell 'em very
much at all - just a fashionable bare minimum.

See, design by accountants. The curmudgeonly spending habits of an
average John Smith of 1960 also determined the design. We have lived
for a considerable time now as an integrated society where product
design is affected by everyone.

Patrick Turner



> Regards,
>
> John Byrns
>
> Surf my web pages at, *http://fmamradios.com/- Hide quoted text -
>
> - Show quoted text -

[John Byrns]

In article >,
Patrick Turner > wrote:

> On May 27, 10:47*am, John Byrns > wrote:
> > In article
> > >,
> > *Patrick Turner > wrote:
> >
> > > On May 23, 5:38*am, John Byrns > wrote:
> > > > In article
> > > > >,
> > > > *Patrick Turner > wrote:
> >
> > > > > Quad-II used a kind of floating paraphase. Nobody much understands
> > > > > exactly how it works but fact is that the output of one EF86 is
> > > > > reduced
> > > > > by resistance divider and fed to the grid of another EF86 and both
> > > > > thus have a stage which effectively has 6dB of local positive FB.
> > > > > Both
> > > > > EF86 have to make up to about 40Vrms for each KT66 grid, ( depending
> > > > > on the load ).
> >
> > > > It's not really that hard to figure out how it works, a lot of the
> > > > quirkiness is
> > > > due to the acrobatics needed to apply negative feedback to the common
> > > > cathode of
> > > > the voltage amplifier and phase splitter. *This was probably a bean
> > > > counter
> > > > thing to eliminate a couple of electrolytic capacitors.
> >
> > > The solution to the problem of low open loop gain suited bean counters
> > > at Quad. But if you make the two EF86 behave as a real LTP with common
> > > cathode R to -400Vdc, or a CCS, and without the mild 6dB PFB boost of
> > > the paraphase inverter principle used, then the differential gain is
> > > halved and if the same amount of NFB was applied globally, you'd need
> > > 2.8Vrms for clipping power instead of only 1.4Vrms.
> >
> > You keep talking about "the mild 6dB PFB boost of the paraphase inverter
> > principle". *I don't understand where you are getting this 6 dB boost? *The
> > floating paraphase has the same gain as the concertina phase inverter, how
> > does
> > the concertina equal the gain of the floating paraphse without PFB, or does
> > the
> > concertina also use PFB? *In any case only one out of the many many
> > possible
> > variations of the floating paraphse could be said to incorporate PFB. *I'm
> > not
> > an expert on the LTP, and am not a big fan of it, I suspect that the truth
> > here
> > is that the LTP throws away 6 dB of gain relative to the concertina and
> > floating
> > paraphase.
>
> With any pair if paraphase input tubes with or without the "floating"
> drive for V2 grid, there is 6dB PFB because you are using a fraction
> of the output from V1 to drive V2. So say tou have a V1 and V2 input
> parphase pair = 6SN7. Each may havea gain = 17, so that from V1 you
> get -17Vo for a +1V input Vgk. The -17Vo V1 output signal is divided
> down to -1Vgk and applied to V2 grid, and the % distortion created by
> V1 is also created in V2, so that distortion is inceased in its
> percentage V2 duely creates its expected +17Vo, and so for only 1Vin
> at V1, you get a total of 34Vo from the two tubes at higher THD %.
> This is certainly true of Quad-II and its feeble use of EF86. I've
> measured it all. Now if the pair of 6SN7 triodes are set up as an LTP
> with one grid taken to 0V, then to get 34Vo you need to apply 2V in,
> and you might say gain is halved because you need 2Vi to get 17Vo from
> each anode. Such an LTP is a form of one common cathode gain tube
> driving a grounded grid tube, but there is no added gain by means of
> PFB, and if the tail is a high R value, there is excellent even order
> H reduction from balanced operation. Try doing some measurements.

I fail to see how doing some measurements would help to answer my question? You
mentioned "PFB" twice again in the above paragraph. My question was, where is
the "PFB in the Paraphase? Most implementations of the paraphase don't have any
"PFB" at all. "PFB" is extremely rare in American paraphase designs, either in
old radios or in tube Hi-Fi. The only version of the paraphase that could be
said to incorporate "PFB" is where V1 & V2 share a common unbypassed cathode
resistor, this scheme is more commonly seen in British designs.

> The concertina "throws away" most of its gain so that +19Vin to a 6SN7
> produces -17Va and +17Vk, with the +2Vgk needed to make the total
> 34Vak output, so open loop gain = 17, but closed loop gain is 34 / 19
> = 1.79, and this has beautiful low THD because the 19dB current NFB
> present.

So the concertina requires 1.12 Volts in for the specified 34V grid to grid
output drive vs. 1.0 Volts in for the paraphase and 2.0 Volts in for the LTP.
1.12 Volts is close enough to 1.0 Volts for Government work, at least it is a
lot closer to 1.0 Volts than it is to 2.0 Volts.

--
Regards,

John Byrns

Surf my web pages at, http://fmamradios.com/

[John Byrns]

In article >,
John L Stewart > wrote:

> Before this thread went off the rails did anyone mention that McIntosh
> uses a seperate winding on the OPT for overall NFB?

A separate winding, a tertiary winding, provides better high frequency stability
than taking the NFB from the secondary winding. The down side of using a
tertiary winding for NFB is that the NFB doesn't include the secondary so that
the damping factor suffers, this probably has no practical consequence, but
doesn't make for good ad copy.

Marantz used an interesting NFB scheme that took the NFB from the secondary at
low frequencies to provide a good damping factor and then used a crossover
filter to take the high frequency NFB from tertiary windings.

--
Regards,

John Byrns

Surf my web pages at, http://fmamradios.com/

[Bret Ludwig[_2_]]

>
> > Quirky old stuff is "my thing", so I stash away old transformers and the like. It does seem however that UK designers took a different tack when designing amps/transformers for this style of feedback. *So the vintage British transformers I have won't simply "drop in". *I'm OK with that.

Yes, you have to respect a thing for what it is and not want it
isn't. I bought an old Plymouth with four doors, a Slant Six and three
on the tree a couple of years ago and sold it. The new owner gutted it
as it didn't have what he wanted, lost interest, and the next guy
pulled off the chrome trim and scrapped it. A perfectly good car
scrapped. *
>
> There have been an amazing number of different amps designed by guys
> who yearned to be unique. "Yearning For Uniqueness" would have to an
> extremely vain pre-occupation of anyone's mind when we consider the
> **** of one man smells almost identically to the **** of the next man
> along. We all like redheads, brunnettes, and blondes, and what we do
> with them is remarkably similar, ie, the divorce rate in the US is
> about the same as in Britain.

I grew up in a house with two parents, a grandmther, and two older
brothers and a sometimes visiting older half sister. If I went into
the bathroom within a few minutes of any of the above having taken a
**** there I could without fail identify which had done so. I knew
everyone's **** smell, all different.
>
> But the implementation of any one amplifier idea is often just as
> important as the idea itself. Ultralinear was the favourite in the US,
> and so was global NFB around 3 gain stages with FB froma speaker
> winding to cathode of V1. The Pomms showed how in the Williamson which
> was a PP triode thinge which quickly became UL if you wanted it to be
> for more power. The americans were fond of power, and their cars were
> bigger, waistlines longer, houses bigger and government more
> influential after WW2. Everything in the USA had to be bigger
> brighter, louder, et all while in Deare Olde England which was savaged
> by WW2 things remained GRIM with housing, rates of pay, and standard
> of living for far longer than in the US after WW2. With smaller houses
> and smaller budgets, only the rich in the UK could buy Quad-II amps
> with the luxury of powerful octal based tubes such as KT66. KT88 had
> to wait until 1957, 12 years after WW2. It wasa time when interest in
> hi-fi was seen by many as vain, vapid, absurd, and eccentric. In my
> observations of audiophiles, I can see that not much has changed.

Socialism ruined Britain postwar. The country has never recovered as
it went from being poor but at least British to being overrun with
immigrants, nonwhite immigrants, none of which have any interest in
being British. The BNP is doing as best it can but too little too
late.
>
>
>
> > > All these old circuits have serious shortcomings which are only made
> > > worse when someone tries to use an unsuitable OPT at home and they do
> > > not understand how NOT to build an oscillator while trying to build an
> > > amplifier.
>
> > Hopefully whatever I pick won't be unsuitable, *but is going to need some changes. *Perhaps in the end the amount of NFB will need to be reduced.
>
> The use of NFB from a dedicated NFB winding which uses fine wire
> because there is little current was something major makers never
> adopted. Baxandal and Williamson were the most ignored blokes of 1950.
> People wanted SIMPLE CHEAP solutions, and these two boffins offered
> neither cheap nor simple, and insisted on going the extra country mile
> to fetch a bucket full of real hi-fi. Baxandall was brilliant, and his
> analysis of the Quad ESL57 requirements of the step up trannies shows
> how damn dumb most consequent people were about basic audio LCR ideas.
> And many online DIY ppl who have tried to build ESL show how dumb they
> continue to be.
>
> Baxandall's amp isn't real bad, but the first input pentode must
> produce a voltage large enough to drive one 6L6 grid in beam tetrode
> mode with fixed Eg2. The other input pentode operates as an inverting
> anode follower with unity gain, but any THD generated in V1 is passed
> on to be reproduced in V2. In effect, driver amp distortion is double
> that of a single tube, and this defect also occurs in any amp using a
> paraphase driver.

The Williamson is *FAR BETTER amp design than
> anything with two pentode input tubes. But in 1950, many designers had
> a real bad case of pentoditis, the affliction where blokes chose a
> pentode instead of two low µ triodes which give much less THD and
> IMD.

Not necessarily. The resulting amp used fewer tubes and therefore was
more reliable. It used less heater power. The Quad worked fine for
decades with the original tube set in many instances, and was much
simpler than the American Mcintosh and it did the job for its intended
market.

The Quad buyer was an affluent sort that just wanted it to play the
music with little fuss. That ti did.

I would advise having a new transformer wound to the original spec if
the amp is worth keeping.

[Bret Ludwig[_2_]]

>
> GE published a book giving 17 amps from 5W to 1,100W and in it they
> recommended both Williamson and paraphase circuits. The best paraphase
> circuits are done using low µ triodes with a following balanced amp so
> that the paraphasing is done at low signal levels where the positive
> FB doesn't increase HD very much because it is so low to begin with.

GEC, not GE. BIG difference.

http://www.tubebooks.org/Books/GEC_approach.pdf

[Bret Ludwig[_2_]]

>
> > there's a general move to create something 'patentable' so that you have
> > a portfolio of intellectual property, regardless of whether or not it is
> > actually better. *But in cases where another guy's patent steps on your
> > design, it might be necessary to go a slightly inferior route to avoid
> > paying royalties. *By now all of those patents are expired.

None the less no one makes a true McIntosh circuit or transformer,
despite the superiority of the basic circuit and the transformer
design.

[Bret Ludwig[_2_]]

On May 24, 6:03*am, John L Stewart <John.L.Stewart.
> wrote:
> Before this thread went off the rails did anyone mention that McIntosh
> uses a seperate winding on the OPT for overall NFB?
>
> Cheers, John
>
> --
> John L Stewart

They use several windings for NFB if you look carefully.

Lots of amplifiers had a tertiary for NFB so the secondary could
float, and that is a very good idea.

[Patrick Turner]

On May 28, 7:59*pm, flipper > wrote:
> On Thu, 26 May 2011 16:32:44 -0700 (PDT), Patrick Turner
>
>
>
>
>
> > wrote:
> >On May 26, 7:35*pm, flipper > wrote:
> >> On Thu, 26 May 2011 00:37:17 -0700 (PDT), Patrick Turner
>
> >> > wrote:
> >> >I mentioned......
> >> >> > I have never seen any commercial design with PFB and NFB -
>
> >> >> Of course you have and I gave you examples the last time you said the
> >> >> same thing.
>
> >> >I've been saying the same thing because I've never seen PFB used in
> >> >commercial amps like the way its done in RDH4 at that amp.
>
> >> Now you've changed it again by adding "like the way."
>
> >> > Sometimes
> >> >bootstrapping is PFB, but usually the gain increase is mild, from gain
> >> >with a load to gain which approaches µ. However, come to think about
> >> >it, Dynaco bootstrapped the pentode input tube anode RL ahead of the
> >> >triode concertina to boost the gain of the pentode.
>
> >> Told ya so.
>
> >> The Harmon Kardon 'Trio' also uses PFB and is the basic topology I've
> >> used in at least three of mine.
>
> >> > The gain with
> >> >bootstrapping a pentode often rises much more than with a triode tube
> >> >because the pentode has its anode feedback screened off from the
> >> >electron stream. Pentode µ is gm x Ra, and as pentode Ra is so high
> >> >then µ is high.
>
> >> >BTW,
> >> >I have to repair the design results of acountants and bean counters
> >> >all too often.
>
> >> You've never had to do it even once because bean counters don't do
> >> design. Never have, don't now, and never will.
>
> >IMHO,
>
> Your 'opinion', and following gibberish, is twaddle. It may fool
> fellow ignorants who, like you, haven't a clue but it's drivel to
> those of us who've worked with your so called 'bean counters' and done
> professional product design.
>
> I don't speak from 'opinion' and cartoons. I speak from fact, having
> been there and done that.

Its OK, every man's facts are another man's fictions, and one man's
trash is another man's treasure.

I just see lots of what I don't want to buy or approve of or want to
be involved in and if everyone was like me the world would collapse.
But fear not and be grateful for the human diversity around you now.

Patrick Turner.

[Patrick Turner]

On May 29, 3:47*am, John Byrns > wrote:
> In article >,
> *Patrick Turner > wrote:
>
>
>
>
>
> > On May 27, 10:47*am, John Byrns > wrote:
> > > In article
> > > >,
> > > *Patrick Turner > wrote:
>
> > > > On May 23, 5:38*am, John Byrns > wrote:
> > > > > In article
> > > > > >,
> > > > > *Patrick Turner > wrote:
>
> > > > > > Quad-II used a kind of floating paraphase. Nobody much understands
> > > > > > exactly how it works but fact is that the output of one EF86 is
> > > > > > reduced
> > > > > > by resistance divider and fed to the grid of another EF86 and both
> > > > > > thus have a stage which effectively has 6dB of local positive FB.

[Patrick Turner]

On May 29, 11:23*am, John Byrns > wrote:
> In article >,
> *John L Stewart > wrote:
>
> > Before this thread went off the rails did anyone mention that McIntosh
> > uses a seperate winding on the OPT for overall NFB?
>
> A separate winding, a tertiary winding, provides better high frequency stability
> than taking the NFB from the secondary winding. *The down side of using a
> tertiary winding for NFB is that the NFB doesn't include the secondary so that
> the damping factor suffers, this probably has no practical consequence, but
> doesn't make for good ad copy.

Yes but the NFB winding position relative to anode turns or secondary
turns will have an effect on what is fed back.
I'd say that if a fine wire NFB winding is wound right over the top of
a thick wire speaker secondary then its signal is near equal to the
speaker's signal and the "error" made by the secondary Rw and LL and
phase shift et all is fed back for correction.
But if the FB tertiary is next to the anode primary then you have a
good hum free FB source with anode signal without LL and Sec Rw
effects and the amp is MUCH easier to stabilise unconditionally. Such
a low voltage and grounded winding gives a conveniently small FB
signal with low source resistance which can be applied to an earlier
stage very effectively. Such a signal picks up a sample of the whole
Va-a, and is a better NFB than using a cap plus R divider from one of
the PP anodes back to an input tube cathode. But bean counters mostly
hated paying for a dedicated NFB tertiary. Why have one when the
speaker secondary exists? Indeed why have one? if you make the OPT
with sufficient interleaving then the Williamson way of NFB is fine,
but bean counters hated Williamson too, and laughed at what he said
makers should do, so we all mainly ended up with OPT with very high LL
and appalling stability problems.
>
> Marantz used an interesting NFB scheme that took the NFB from the secondary at
> low frequencies to provide a good damping factor and then used a crossover
> filter to take the high frequency NFB from tertiary windings.

I'm not sure about that one. Some makers just used the speaker sec for
normal global NFB with R divider to feed V1 cathode but then the cap
that is normally strapped across the FB R to advance the phase of the
fed back signal at HF is not used, but a cap from V1 cathode is taken
to one of the OP tube anodes. I've always found no real joy in such
measures and I prefer the normal conventional Williamson idea where
one makes the OPT have wide BW which then pushes the regions where
instabilty occurs further below and above the AF band and thus to
where its easy to instal gain reducing and phase tailoring networks
while maintaining 10Hz to 65kHz full power bandwidth with complete
stability and 20dB global NFB is desired. I'll follow the Williamson
principles before I'll follow any others. I happen to like using
tertiary windings for NFB myself, but in the form of CFB windings
which are a part of the OPT primary and which carry Ia. Its the
Acoustical. Thus the OP stage is substantially linearised and given
the character of triode Ra and low THD while retaining the tertrode
AB1 or A1 power. Then only 10dB of global NFB is needed, if any at
all.

Patrick Turner.



>
> --
> Regards,
>
> John Byrns
>
> Surf my web pages at, *http://fmamradios.com/

[Patrick Turner]

On May 29, 10:25*pm, flipper > wrote:
> On Fri, 27 May 2011 17:42:35 -0700 (PDT), Patrick Turner
>
>
>
>
>
> > wrote:
> >On May 27, 10:47*am, John Byrns > wrote:
> >> In article >,
> >> *Patrick Turner > wrote:
>
> >> > On May 23, 5:38*am, John Byrns > wrote:
> >> > > In article
> >> > > >,
> >> > > *Patrick Turner > wrote:
>
> >> > > > Quad-II used a kind of floating paraphase. Nobody much understands
> >> > > > exactly how it works but fact is that the output of one EF86 is
> >> > > > reduced
> >> > > > by resistance divider and fed to the grid of another EF86 and both
> >> > > > thus have a stage which effectively has 6dB of local positive FB.. Both
> >> > > > EF86 have to make up to about 40Vrms for each KT66 grid, ( depending
> >> > > > on the load ).
>
> >> > > It's not really that hard to figure out how it works, a lot of the
> >> > > quirkiness is
> >> > > due to the acrobatics needed to apply negative feedback to the common
> >> > > cathode of
> >> > > the voltage amplifier and phase splitter. *This was probably a bean counter
> >> > > thing to eliminate a couple of electrolytic capacitors.
>
> >> > The solution to the problem of low open loop gain suited bean counters
> >> > at Quad. But if you make the two EF86 behave as a real LTP with common
> >> > cathode R to -400Vdc, or a CCS, and without the mild 6dB PFB boost of
> >> > the paraphase inverter principle used, then the differential gain is
> >> > halved and if the same amount of NFB was applied globally, you'd need
> >> > 2.8Vrms for clipping power instead of only 1.4Vrms.
>
> >> You keep talking about "the mild 6dB PFB boost of the paraphase inverter
> >> principle". *I don't understand where you are getting this 6 dB boost? *The
> >> floating paraphase has the same gain as the concertina phase inverter, how does
> >> the concertina equal the gain of the floating paraphse without PFB, or does the
> >> concertina also use PFB? *In any case only one out of the many many possible
> >> variations of the floating paraphse could be said to incorporate PFB. *I'm not
> >> an expert on the LTP, and am not a big fan of it, I suspect that the truth here
> >> is that the LTP throws away 6 dB of gain relative to the concertina and floating
> >> paraphase.
>
> >With any pair if paraphase input tubes with or without the "floating"
> >drive for V2 grid,
>
> It makes a difference which.
>
> > there is 6dB PFB because you are using a fraction
> >of the output from V1 to drive V2. So say tou have a V1 and V2 input
> >parphase pair = 6SN7. Each may havea gain = 17, so that from V1 you
> >get -17Vo for a +1V input Vgk. The -17Vo V1 output signal is divided
> >down to -1Vgk and applied to V2 grid, and the % distortion created by
> >V1 is also created in V2, so that distortion is inceased in its
> >percentage V2 duely creates its expected +17Vo, and so for only 1Vin
> >at V1, you get a total of 34Vo from the two tubes at higher THD %.
>
> The 'plain' paraphase you describe is simply two gain stages with an
> intermediate attenuator and, in that regard, is no different than,
> say, a volume control stage with the knob turned to a 1/17 ratio.
>
> That, in the paraphase, the ratio is fixed and one observes the two
> signals are of opposite phase doesn't magically turn it into positive
> feedback. It's still simply two gain stages with the attenuation
> 'specifically selected' for the purpose.
>
> The floating paraphase is a different beast and uses negative
> feedback. In that regard it's similar to the concertina except it uses
> two summing resistors to the grid for unity gain rather than cathode
> follower feedback, but they both use NFB to reduce distortion in the
> second tube and have similar gain.
>
> The concertina's topology makes it inherently balanced but also limits
> it's use to triodes while the floating paraphase can use pentodes for
> greater levels of NFB, with the balance of both types being limited by
> resistor tolerances. The floating paraphase is also capable of larger
> output voltage swing than the concertina.
>
> None of them, however, use PFB in the basic circuit.
>
> >This is certainly true of Quad-II and its feeble use of EF86. I've
> >measured it all. Now if the pair of 6SN7 triodes are set up as an LTP
> >with one grid taken to 0V, then to get 34Vo you need to apply 2V in,
> >and you might say gain is halved because you need 2Vi to get 17Vo from
> >each anode. Such an LTP is a form of one common cathode gain tube
> >driving a grounded grid tube, but there is no added gain by means of
> >PFB, and if the tail is a high R value, there is excellent even order
> >H reduction from balanced operation. Try doing some measurements.
>
> The "even order H reduction" comes from OPT summing of the two phases,
> not the LTP itself.
>
> However, even if one had a 'perfect' CCS you do not end up with
> 'perfectly balanced' LTP outputs because of the tubes. Current may be
> constant but the voltages in each tube to produce those currents are
> not identical and it's the voltages which are propagated as signals.
> Plus, of course, the ever present resistor tolerances.
>
> >The concertina "throws away" most of its gain so that +19Vin to a 6SN7
> >produces -17Va and +17Vk, with the +2Vgk needed to make the total
> >34Vak output, so open loop gain = 17, but closed loop gain is 34 / 19
> >= 1.79, and this has beautiful low THD because the 19dB current NFB
> >present.
>
> The floating paraphase, if using the same tubes, has the same NFB.

Your reasoning seems so flawed to me that I'd waste too much of my
precious time to refute everything you've said which doesn't add up.

I humbly suggest you do a pile of basic measurements like I did and
you may conclude that the paraphase is a impure way and a poor man's
way to boost gain by mild PFB.

I've never seen fit to ever use any kind of paraphase connection of
input or driver tubes. I have my reasons which remain obscure to you.

Don't let that stop you using a paraphase though; usually the defects
of paraphase won't cripple the music.

Patrick Turner.

[Patrick Turner]

On May 30, 9:38*am, Bret Ludwig > wrote:
> > > Quirky old stuff is "my thing", so I stash away old transformers and the like. It does seem however that UK designers took a different tack when designing amps/transformers for this style of feedback. *So the vintage British transformers I have won't simply "drop in". *I'm OK with that.
>
> *Yes, you have to respect a thing for what it is and not want it
> isn't. I bought an old Plymouth with four doors, a Slant Six and three
> on the tree a couple of years ago and sold it. The new owner gutted it
> as it didn't have what he wanted, lost interest, and the next guy
> pulled off the chrome trim and scrapped it. A perfectly good car
> scrapped. *
>
>
>
> > There have been an amazing number of different amps designed by guys
> > who yearned to be unique. "Yearning For Uniqueness" would have to an
> > extremely vain pre-occupation of anyone's mind when we consider the
> > **** of one man smells almost identically to the **** of the next man
> > along. We all like redheads, brunnettes, and blondes, and what we do
> > with them is remarkably similar, ie, the divorce rate in the US is
> > about the same as in Britain.
>
> *I grew up in a house with two parents, a grandmther, and two older
> brothers and a sometimes visiting older half sister. If I went into
> the bathroom within a few minutes of any of the above having taken a
> **** there I could without fail identify which had done so. I knew
> everyone's **** smell, all different.

Ah, well, your powers of perception are remarkable, bearing in mind
your fascinations, and, but, unlike yourself, it must have been my
almost complete dis-interest in the smell of the other 7 ppl in the
house I grew up i that i completely missed out on knowing whose crap
was whose, or else perhaps the toilet in our house was better
ventilated than in yours. :-)
>
> > But the implementation of any one amplifier idea is often just as
> > important as the idea itself. Ultralinear was the favourite in the US,
> > and so was global NFB around 3 gain stages with FB froma speaker
> > winding to cathode of V1. The Pomms showed how in the Williamson which
> > was a PP triode thinge which quickly became UL if you wanted it to be
> > for more power. The americans were fond of power, and their cars were
> > bigger, waistlines longer, houses bigger and government more
> > influential after WW2. Everything in the USA had to be bigger
> > brighter, louder, et all while in Deare Olde England which was savaged
> > by WW2 things remained GRIM with housing, rates of pay, and standard
> > of living for far longer than in the US after WW2. With smaller houses
> > and smaller budgets, only the rich in the UK could buy Quad-II amps
> > with the luxury of powerful octal based tubes such as KT66. KT88 had
> > to wait until 1957, 12 years after WW2. It was a time when interest in
> > hi-fi was seen by many as vain, vapid, absurd, and eccentric. In my
> > observations of audiophiles, I can see that not much has changed.
>
> *Socialism ruined Britain postwar. The country has never recovered as
> it went from being poor but at least British to being overrun with
> immigrants, nonwhite immigrants, none of which have any interest in
> being British. The BNP is doing as best it can but too little too
> late.

So where were you when ya could have lent them your machine gun to
make Britain a better place?

Oh, I guess you really hate all those Mexicans crossing the border
too, yet they do all the dirty work so nice and cheap now don't they?

Probably you hate a browned skin man being President Of the USA, and
giving speaches in Ireland last week which would have been totally
beyond the capability of Dubbya, or of Sarah Palin.
>
>
> > > > All these old circuits have serious shortcomings which are only made
> > > > worse when someone tries to use an unsuitable OPT at home and they do
> > > > not understand how NOT to build an oscillator while trying to build an
> > > > amplifier.
>
> > > Hopefully whatever I pick won't be unsuitable, *but is going to need some changes. *Perhaps in the end the amount of NFB will need to be reduced.
>
> > The use of NFB from a dedicated NFB winding which uses fine wire
> > because there is little current was something major makers never
> > adopted. Baxandal and Williamson were the most ignored blokes of 1950.
> > People wanted SIMPLE CHEAP solutions, and these two boffins offered
> > neither cheap nor simple, and insisted on going the extra country mile
> > to fetch a bucket full of real hi-fi. Baxandall was brilliant, and his
> > analysis of the Quad ESL57 requirements of the step up trannies shows
> > how damn dumb most consequent people were about basic audio LCR ideas.
> > And many online DIY ppl who have tried to build ESL show how dumb they
> > continue to be.
>
> > Baxandall's amp isn't real bad, but the first input pentode must
> > produce a voltage large enough to drive one 6L6 grid in beam tetrode
> > mode with fixed Eg2. The other input pentode operates as an inverting
> > anode follower with unity gain, but any THD generated in V1 is passed
> > on to be reproduced in V2. In effect, driver amp distortion is double
> > that of a single tube, and this defect also occurs in any amp using a
> > paraphase driver.
>
> The Williamson is *FAR BETTER amp design than
>
> > anything with two pentode input tubes. But in 1950, many designers had
> > a real bad case of pentoditis, the affliction where blokes chose a
> > pentode instead of two low µ triodes which give much less THD and
> > IMD.
>
> *Not necessarily. The resulting amp used fewer tubes and therefore was
> more reliable. It used less heater power. The Quad worked fine for
> decades with the original tube set in many instances, and was much
> simpler than the American Mcintosh and it did the job for its intended
> market.
>
> *The Quad buyer was an affluent sort that just wanted it to play the
> music with little fuss. That ti did.

The Quad-II was a lot better than much other worse garbage being
flogged to a gullible public in 1960. But its easy to make a better
sounding amp than Quad-II with the same 2 x KT66 and same number of
input tube sockets where a EF86 in triode would make a nice SE input
tube and then you have LTP driver/phase inverter with 6CG7.

As long as 3 pairs of mint quads are in a museum someplace, I'm happy.
But all the rest are worth complete re-wiring. I have a pair underway
here where I have wound much better OPT than the terrible originals.

Unlike ppl who ruin nice old cars, I create something far better while
making use of the basics like chassis and PT. I finish what I start.

Patrick Turner.
>
> *I would advise having a new transformer wound to the original spec if
> the amp is worth keeping.-

Yeah, very nice idea, but who can ever do EXACTLY what was done 50
years ago?

To me the past is gone, there is only the future in which lessons of
the past may be incorperated without the shortcomings of the past.

Patrick Turner.

[Patrick Turner]

On May 30, 8:43*pm, Patrick Turner > wrote:
> On May 30, 9:38*am, Bret Ludwig > wrote:
>
>
>
>
>
> > > > Quirky old stuff is "my thing", so I stash away old transformers and the like. It does seem however that UK designers took a different tack when designing amps/transformers for this style of feedback. *So the vintage British transformers I have won't simply "drop in". *I'm OK with that.
>
> > *Yes, you have to respect a thing for what it is and not want it
> > isn't. I bought an old Plymouth with four doors, a Slant Six and three
> > on the tree a couple of years ago and sold it. The new owner gutted it
> > as it didn't have what he wanted, lost interest, and the next guy
> > pulled off the chrome trim and scrapped it. A perfectly good car
> > scrapped. *
>
> > > There have been an amazing number of different amps designed by guys
> > > who yearned to be unique. "Yearning For Uniqueness" would have to an
> > > extremely vain pre-occupation of anyone's mind when we consider the
> > > **** of one man smells almost identically to the **** of the next man
> > > along. We all like redheads, brunnettes, and blondes, and what we do
> > > with them is remarkably similar, ie, the divorce rate in the US is
> > > about the same as in Britain.
>
> > *I grew up in a house with two parents, a grandmther, and two older
> > brothers and a sometimes visiting older half sister. If I went into
> > the bathroom within a few minutes of any of the above having taken a
> > **** there I could without fail identify which had done so. I knew
> > everyone's **** smell, all different.
>
> Ah, well, your powers of perception are remarkable, bearing in mind
> your fascinations, and, but, unlike yourself, it must have been my
> almost complete dis-interest in the smell of the other 7 ppl in the
> house I grew up i that i completely missed out on knowing whose crap
> was whose, or else perhaps the toilet in our house was better
> ventilated than in yours. :-)
>
>
>
>
>
>
>
> > > But the implementation of any one amplifier idea is often just as
> > > important as the idea itself. Ultralinear was the favourite in the US,
> > > and so was global NFB around 3 gain stages with FB froma speaker
> > > winding to cathode of V1. The Pomms showed how in the Williamson which
> > > was a PP triode thinge which quickly became UL if you wanted it to be
> > > for more power. The americans were fond of power, and their cars were
> > > bigger, waistlines longer, houses bigger and government more
> > > influential after WW2. Everything in the USA had to be bigger
> > > brighter, louder, et all while in Deare Olde England which was savaged
> > > by WW2 things remained GRIM with housing, rates of pay, and standard
> > > of living for far longer than in the US after WW2. With smaller houses
> > > and smaller budgets, only the rich in the UK could buy Quad-II amps
> > > with the luxury of powerful octal based tubes such as KT66. KT88 had
> > > to wait until 1957, 12 years after WW2. It was a time when interest in
> > > hi-fi was seen by many as vain, vapid, absurd, and eccentric. In my
> > > observations of audiophiles, I can see that not much has changed.
>
> > *Socialism ruined Britain postwar. The country has never recovered as
> > it went from being poor but at least British to being overrun with
> > immigrants, nonwhite immigrants, none of which have any interest in
> > being British. The BNP is doing as best it can but too little too
> > late.
>
> So where were you when ya could have lent them your machine gun to
> make Britain a better place?
>
> Oh, I guess you really hate all those Mexicans crossing the border
> too, yet they do all the dirty work so nice and cheap now don't they?
>
> Probably you hate a browned skin man being President Of the USA, and
> giving speaches in Ireland last week which would have been totally
> beyond the capability of Dubbya, or of Sarah Palin.
>
>
>
>
>
>
>
> > > > > All these old circuits have serious shortcomings which are only made
> > > > > worse when someone tries to use an unsuitable OPT at home and they do
> > > > > not understand how NOT to build an oscillator while trying to build an
> > > > > amplifier.
>
> > > > Hopefully whatever I pick won't be unsuitable, *but is going to need some changes. *Perhaps in the end the amount of NFB will need to be reduced.
>
> > > The use of NFB from a dedicated NFB winding which uses fine wire
> > > because there is little current was something major makers never
> > > adopted. Baxandal and Williamson were the most ignored blokes of 1950..
> > > People wanted SIMPLE CHEAP solutions, and these two boffins offered
> > > neither cheap nor simple, and insisted on going the extra country mile
> > > to fetch a bucket full of real hi-fi. Baxandall was brilliant, and his
> > > analysis of the Quad ESL57 requirements of the step up trannies shows
> > > how damn dumb most consequent people were about basic audio LCR ideas..
> > > And many online DIY ppl who have tried to build ESL show how dumb they
> > > continue to be.
>
> > > Baxandall's amp isn't real bad, but the first input pentode must
> > > produce a voltage large enough to drive one 6L6 grid in beam tetrode
> > > mode with fixed Eg2. The other input pentode operates as an inverting
> > > anode follower with unity gain, but any THD generated in V1 is passed
> > > on to be reproduced in V2. In effect, driver amp distortion is double
> > > that of a single tube, and this defect also occurs in any amp using a
> > > paraphase driver.
>
> > The Williamson is *FAR BETTER amp design than
>
> > > anything with two pentode input tubes. But in 1950, many designers had
> > > a real bad case of pentoditis, the affliction where blokes chose a
> > > pentode instead of two low µ triodes which give much less THD and
> > > IMD.
>
> > *Not necessarily. The resulting amp used fewer tubes and therefore was
> > more reliable. It used less heater power. The Quad worked fine for
> > decades with the original tube set in many instances, and was much
> > simpler than the American Mcintosh and it did the job for its intended
> > market.
>
> > *The Quad buyer was an affluent sort that just wanted it to play the
> > music with little fuss. That ti did.
>
> The Quad-II was a lot better than much other worse garbage being
> flogged to a gullible public in 1960. But its easy to make a better
> sounding amp than Quad-II with the same 2 x KT66 and same number of
> input tube sockets where a EF86 in triode would make a nice SE input
> tube and then you have LTP driver/phase inverter with 6CG7.
>
> As long as 3 pairs of mint quads are in a museum someplace, I'm happy.
> But all the rest are worth complete re-wiring. I have a pair underway
> here where I have wound much better OPT than the terrible originals.
>
> Unlike ppl who ruin nice old cars, I create something far better while
> making use of the basics like chassis and PT. I finish what I start.
>
> Patrick Turner.
>
>
>
> > *I would advise having a new transformer wound to the original spec if
> > the amp is worth keeping.-
>
> Yeah, very nice idea, but who can ever do EXACTLY what was done 50
> years ago?
>
> To me the past is gone, there is only the future in which lessons of
> the past may be incorperated without the shortcomings of the past.
>
> Patrick Turner.- Hide quoted text -
>
> - Show quoted text -- Hide quoted text -
>
> - Show quoted text -- Hide quoted text -
>
> - Show quoted text -

[Patrick Turner]

On May 30, 9:44*am, Bret Ludwig > wrote:
> > GE published a book giving 17 amps from 5W to 1,100W and in it they
> > recommended both Williamson and paraphase circuits. The best paraphase
> > circuits are done using low µ triodes with a following balanced amp so
> > that the paraphasing is done at low signal levels where the positive
> > FB doesn't increase HD very much because it is so low to begin with.
>
> *GEC, not GE. BIG difference.
>
> http://www.tubebooks.org/Books/GEC_approach.pdf

Indeed. Everyone should have a copy of the GEC book.

Patrick Turner.

[Patrick Turner]

On May 30, 7:51*pm, flipper > wrote:
> On Mon, 30 May 2011 02:23:45 -0700 (PDT), Patrick Turner
>
>
>
>
>
> > wrote:
> >On May 28, 7:59*pm, flipper > wrote:
> >> On Thu, 26 May 2011 16:32:44 -0700 (PDT), Patrick Turner
>
> >> > wrote:
> >> >On May 26, 7:35*pm, flipper > wrote:
> >> >> On Thu, 26 May 2011 00:37:17 -0700 (PDT), Patrick Turner
>
> >> >> > wrote:
> >> >> >I mentioned......
> >> >> >> > I have never seen any commercial design with PFB and NFB -
>
> >> >> >> Of course you have and I gave you examples the last time you said the
> >> >> >> same thing.
>
> >> >> >I've been saying the same thing because I've never seen PFB used in
> >> >> >commercial amps like the way its done in RDH4 at that amp.
>
> >> >> Now you've changed it again by adding "like the way."
>
> >> >> > Sometimes
> >> >> >bootstrapping is PFB, but usually the gain increase is mild, from gain
> >> >> >with a load to gain which approaches µ. However, come to think about
> >> >> >it, Dynaco bootstrapped the pentode input tube anode RL ahead of the
> >> >> >triode concertina to boost the gain of the pentode.
>
> >> >> Told ya so.
>
> >> >> The Harmon Kardon 'Trio' also uses PFB and is the basic topology I've
> >> >> used in at least three of mine.
>
> >> >> > The gain with
> >> >> >bootstrapping a pentode often rises much more than with a triode tube
> >> >> >because the pentode has its anode feedback screened off from the
> >> >> >electron stream. Pentode µ is gm x Ra, and as pentode Ra is so high
> >> >> >then µ is high.
>
> >> >> >BTW,
> >> >> >I have to repair the design results of acountants and bean counters
> >> >> >all too often.
>
> >> >> You've never had to do it even once because bean counters don't do
> >> >> design. Never have, don't now, and never will.
>
> >> >IMHO,
>
> >> Your 'opinion', and following gibberish, is twaddle. It may fool
> >> fellow ignorants who, like you, haven't a clue but it's drivel to
> >> those of us who've worked with your so called 'bean counters' and done
> >> professional product design.
>
> >> I don't speak from 'opinion' and cartoons. I speak from fact, having
> >> been there and done that.
>
> >Its OK, every man's facts are another man's fictions, and one man's
> >trash is another man's treasure.
>
> More gibberish. Go bang your head on a wall and see how far you get
> wishing it were 'fiction' rather than solid fact.
>
> >I just see lots of what I don't want to buy or approve of or want to
> >be involved in and if everyone was like me the world would collapse.
> >But fear not and be grateful for the human diversity around you now.
>
> It should be blindingly obvious by now that you are not representative
> of the market.
>
> Of course, it's also blindingly obvious that accountants are trained
> in accounting, which is pretty much why they're called accountants,
> and not design but, then, it being obvious to everyone else has never
> stopped your delusions yet.

I agree almost entirely. Acountants are acountants. No ****in doubt
about it. They count beans, so to speak.
And so often one will say to a CEO, "Jesus Fred, doncha reckon if the
OPT was smaller and lighter you'd make more profit?" CEO replies,
"Yeah, your'e right again Bill, let's talk to the winder guy...", and
its a little more quality demolished by a bean counter.

Similar crap conversations happen in BP which polluted the gulf so
badly......the all mighty DOOLAH must be worshpipped and the true
price which should be paid is avoided.

Human failings have few limitations.

People can resist all sorts of things, except temptations.

Patrick Turner.

[John Byrns]

In article >,
Patrick Turner > wrote:

> On May 29, 3:47*am, John Byrns > wrote:
> > In article
> > >,
> > *Patrick Turner > wrote:
>
> Well, I can't explain it any better than I have. If circuit gain is
> increased by feeding back a fraction of an output signal of one stage
> to an earlier stage and the gain is increased, THD increased,
> bandwidth reduced, then I'd say PFB exists. We see feathers, a ducks
> bill, wings and webbed feet, a ducks tail that wags and we say there's
> a duck.

Unfortunately this is a completely incorrect description of how a generic
paraphase inverter operates, so the duck analogy doesn't apply.

> > > The concertina "throws away" most of its gain so that +19Vin to a 6SN7
> > > produces -17Va and +17Vk, with the +2Vgk needed to make the total
> > > 34Vak output, so open loop gain = 17, but closed loop gain is 34 / 19
> > > = 1.79, and this has beautiful low THD because the 19dB current NFB
> > > present.
> >
> > So the concertina requires 1.12 Volts in for the specified 34V grid to grid
> > output drive vs. 1.0 Volts in for the paraphase and 2.0 Volts in for the
> > LTP. *
> > 1.12 Volts is close enough to 1.0 Volts for Government work, at least it is
> > a
> > lot closer to 1.0 Volts than it is to 2.0 Volts.
>
> The paraphase tends to add gain "artificially" for a given number of
> tubes, moreso than merely cascading them.

"artificial" gain is the best kind, it can be made so pure that its sound is
simply sublime.

> And in the case of Quad-II, the KT66 grids are biased via 680k Rgs,
> and one has a 2k7 at its bottom from which the signal to V2 pentode
> grid is wrought.
> Now that 2k7 is just what Walker chose, but it could be a range of
> values; if larger, there's more PFB and more gain and weird things
> happen when you increase that
> 2k7 too much because there is a definite limit to the amount of PFB
> which can be applied without terrible instability.

I don't know if 2k7 is the correct value for this resistor, I assume that Quad
choose correctly here, there is only one correct value for this resistor where
the circuit will function properly, other values are not an option! Changing
the value of this resistor will change the amount of PFB as you say, thereby
changing the gain of V1. The problem with changing the value of this resistor
away from the correct value, to some other value, is that in addition to
changing the amount of PFB, it also unbalances the phase inverter so that the
two output tubes don't receive the same amount of drive voltage.

> Next time you play around with a paraphase stage, try tinkering with R
> diver values and drive from V1 to V2. Interesting stuff happens, with
> not much of it of real value.

What exactly are "R diver values"? There is only one correct value for the
"drive from V1 to V2", you may find other amounts of drive interesting, I'm not
sure why though?

--
Regards,

John Byrns

Surf my web pages at, http://fmamradios.com/

[John Byrns]

In article >,
Patrick Turner > wrote:

> On May 29, 11:23*am, John Byrns > wrote:
> > In article >,
> > *John L Stewart > wrote:
> >
> > > Before this thread went off the rails did anyone mention that McIntosh
> > > uses a seperate winding on the OPT for overall NFB?
> >
> > A separate winding, a tertiary winding, provides better high frequency
> > stability
> > than taking the NFB from the secondary winding. *The down side of using a
> > tertiary winding for NFB is that the NFB doesn't include the secondary so
> > that
> > the damping factor suffers, this probably has no practical consequence, but
> > doesn't make for good ad copy.
>
> Yes but the NFB winding position relative to anode turns or secondary
> turns will have an effect on what is fed back.

Yes, the design/positioning of the tertiary winding affects the leakage
inductances between the various windings

> I'd say that if a fine wire NFB winding is wound right over the top of
> a thick wire speaker secondary then its signal is near equal to the
> speaker's signal and the "error" made by the secondary Rw and LL and
> phase shift et all is fed back for correction.

No tertiary can correct for the "Rw" of the secondary!

> But if the FB tertiary is next to the anode primary then you have a
> good hum free FB source with anode signal without LL and Sec Rw
> effects and the amp is MUCH easier to stabilise unconditionally. Such
> a low voltage and grounded winding gives a conveniently small FB
> signal with low source resistance which can be applied to an earlier
> stage very effectively. Such a signal picks up a sample of the whole
> Va-a, and is a better NFB than using a cap plus R divider from one of
> the PP anodes back to an input tube cathode. But bean counters mostly
> hated paying for a dedicated NFB tertiary. Why have one when the
> speaker secondary exists? Indeed why have one? if you make the OPT
> with sufficient interleaving then the Williamson way of NFB is fine,
> but bean counters hated Williamson too, and laughed at what he said
> makers should do, so we all mainly ended up with OPT with very high LL
> and appalling stability problems.
> >
> > Marantz used an interesting NFB scheme that took the NFB from the secondary
> > at
> > low frequencies to provide a good damping factor and then used a crossover
> > filter to take the high frequency NFB from tertiary windings.
>
> I'm not sure about that one. Some makers just used the speaker sec for
> normal global NFB with R divider to feed V1 cathode but then the cap
> that is normally strapped across the FB R to advance the phase of the
> fed back signal at HF is not used, but a cap from V1 cathode is taken
> to one of the OP tube anodes. I've always found no real joy in such
> measures and I prefer the normal conventional Williamson idea where
> one makes the OPT have wide BW which then pushes the regions where
> instabilty occurs further below and above the AF band and thus to
> where its easy to instal gain reducing and phase tailoring networks
> while maintaining 10Hz to 65kHz full power bandwidth with complete
> stability and 20dB global NFB is desired. I'll follow the Williamson
> principles before I'll follow any others. I happen to like using
> tertiary windings for NFB myself, but in the form of CFB windings
> which are a part of the OPT primary and which carry Ia. Its the
> Acoustical. Thus the OP stage is substantially linearised and given
> the character of triode Ra and low THD while retaining the tertrode
> AB1 or A1 power. Then only 10dB of global NFB is needed, if any at
> all.

CFB is nice, but it does increase the demands on the driver stage substantially.

--
Regards,

John Byrns

Surf my web pages at, http://fmamradios.com/

[Bret Ludwig[_2_]]

> So where were you when ya could have lent them your machine gun to
> make Britain a better place?
>
> Oh, I guess you really hate all those Mexicans crossing the border
> too, yet they do all the dirty work so nice and cheap now don't they?
>
> Probably you hate a browned skin man being President Of the USA, and
> giving speaches in Ireland last week which would have been totally
> beyond the capability of Dubbya, or of Sarah Palin.

I preferred Obama to McCain in fact as did most WNs. He has been a
disappointment to be sure but any other candidate would have been as
well who would have been likely to have been nominated.

I don't hate the Mexicans, although I acknowledge that the Mexicans
coming here are mostly the browner and stupider ones who can't make it
back home. I detest the fact that our politicians won't do what any
nation has to do which is secure its borders and throw out violators.
The Republicans want cheap labor to undercut the American worker, both
black and white, and the Dems want the illegals to vote, and vote
Democratic, which they will.

Machine gunning people is not the answer. Enforcing the law firmly
and acknowledging that we are White countries who should and must stay
that way is. No one race is "superior", but we are who we are and
should stay that way. Britain should be for the British and America
for the Americans.

[Bret Ludwig[_2_]]

On Mon, 30 May 2011 02:23:45 -0700 (PDT), Patrick Turner

- Hide quoted text -
- Show quoted text -
> wrote:
>On May 28, 7:59 pm, flipper > wrote:
>> On Thu, 26 May 2011 16:32:44 -0700 (PDT), Patrick Turner

>> > wrote:
>> >On May 26, 7:35 pm, flipper > wrote:
>> >> On Thu, 26 May 2011 00:37:17 -0700 (PDT), Patrick Turner

>> >> > wrote:
>> >> >I mentioned......
>> >> >> > I have never seen any commercial design with PFB and NFB -

>> >> >> Of course you have and I gave you examples the last time you said the
>> >> >> same thing.

>> >> >I've been saying the same thing because I've never seen PFB used in
>> >> >commercial amps like the way its done in RDH4 at that amp.

>> >> Now you've changed it again by adding "like the way."

>> >> > Sometimes
>> >> >bootstrapping is PFB, but usually the gain increase is mild, from gain
>> >> >with a load to gain which approaches µ. However, come to think about
>> >> >it, Dynaco bootstrapped the pentode input tube anode RL ahead of the
>> >> >triode concertina to boost the gain of the pentode.

>> >> Told ya so.

>> >> The Harmon Kardon 'Trio' also uses PFB and is the basic topology I've
>> >> used in at least three of mine.

>> >> > The gain with
>> >> >bootstrapping a pentode often rises much more than with a triode tube
>> >> >because the pentode has its anode feedback screened off from the
>> >> >electron stream. Pentode µ is gm x Ra, and as pentode Ra is so high
>> >> >then µ is high.

>> >> >BTW,
>> >> >I have to repair the design results of acountants and bean counters
>> >> >all too often.

>> >> You've never had to do it even once because bean counters don't do
>> >> design. Never have, don't now, and never will.

>> >IMHO,

>> Your 'opinion', and following gibberish, is twaddle. It may fool
>> fellow ignorants who, like you, haven't a clue but it's drivel to
>> those of us who've worked with your so called 'bean counters' and done
>> professional product design.

>> I don't speak from 'opinion' and cartoons. I speak from fact, having
>> been there and done that.

>Its OK, every man's facts are another man's fictions, and one man's
>trash is another man's treasure.

More gibberish. Go bang your head on a wall and see how far you get
wishing it were 'fiction' rather than solid fact.

>I just see lots of what I don't want to buy or approve of or want to
>be involved in and if everyone was like me the world would collapse.
>But fear not and be grateful for the human diversity around you now.

It should be blindingly obvious by now that you are not representative
of the market.

Of course, it's also blindingly obvious that accountants are trained
in accounting, which is pretty much why they're called accountants,
and not design but, then, it being obvious to everyone else has never
stopped your delusions yet.



It's true that more robust construction would have made these things
last longer, but to be fair, no one realistically figured anyone would
be running these things fifty or sixty years hence.


Saul Marantz (yes, I know) was determined to make the finest quality
hi-fi equipment and spared little in the quest to do so. His build
cost was double and then some of what his nearest competitor,
McIntosh, spent per unit.

Avery Fisher (yes, he was too) was more mainstream but still put a
lot of build cost in his product as compared to his competitors.

Both businesses are out of business in terms of being an American
manufacturer. McIntosh is also owned by Japanese, BUT are allowed to
operate autonomously and they are still manufacturing in Binghamton.

We can look at the classic Mac products and say there were several
aspects where they could have done better but the salient fact is,,
they are still here.

Quad never set out to be the technical ulimate but to be a usable
integrated system and they succeeded marvelously.

Even the Dynaco ST70, which I have slammed long and hard, has to be
admitted as having been insanely successful in its day. By the
standards of its day it was a great product because a college kid
could afford a Dyna pre and ST70, and AR table and an AR acoustic
suspension speaker set in 1963. Some portable record player outfits
cost nearly as much. Again, no one realistically thought thay would be
running in 2011.

Had the dyna been "built right" it would have had to cost more, maybe
considerably more. One area where they shaved was weight to meat a
Railway Express shipping target. That's why the power transformer is
undersize. The profit margins in this stuff were minimal.

It's like a car. Yeah, if ALL the Ford Mustangs had had 9 inch rears,
five bolt disc brake setups and so forth they'd have been better cars,
but 90% of them were going to the crusher in five or six years anyway.
If they had overbuilt them it would have made little difference in
this rate. A great many cars get driven to the crusher under their own
power.

[Patrick Turner]

On May 31, 3:10*pm, Bret Ludwig > wrote:
> On Mon, 30 May 2011 02:23:45 -0700 (PDT), Patrick Turner
>
> - Hide quoted text -
> - Show quoted text -
>
>
>
>
>
> > wrote:
> >On May 28, 7:59 pm, flipper > wrote:
> >> On Thu, 26 May 2011 16:32:44 -0700 (PDT), Patrick Turner
> >> > wrote:
> >> >On May 26, 7:35 pm, flipper > wrote:
> >> >> On Thu, 26 May 2011 00:37:17 -0700 (PDT), Patrick Turner
> >> >> > wrote:
> >> >> >I mentioned......
> >> >> >> > I have never seen any commercial design with PFB and NFB -
> >> >> >> Of course you have and I gave you examples the last time you said the
> >> >> >> same thing.
> >> >> >I've been saying the same thing because I've never seen PFB used in
> >> >> >commercial amps like the way its done in RDH4 at that amp.
> >> >> Now you've changed it again by adding "like the way."
> >> >> > Sometimes
> >> >> >bootstrapping is PFB, but usually the gain increase is mild, from gain
> >> >> >with a load to gain which approaches µ. However, come to think about
> >> >> >it, Dynaco bootstrapped the pentode input tube anode RL ahead of the
> >> >> >triode concertina to boost the gain of the pentode.
> >> >> Told ya so.
> >> >> The Harmon Kardon 'Trio' also uses PFB and is the basic topology I've
> >> >> used in at least three of mine.
> >> >> > The gain with
> >> >> >bootstrapping a pentode often rises much more than with a triode tube
> >> >> >because the pentode has its anode feedback screened off from the
> >> >> >electron stream. Pentode µ is gm x Ra, and as pentode Ra is so high
> >> >> >then µ is high.
> >> >> >BTW,
> >> >> >I have to repair the design results of acountants and bean counters
> >> >> >all too often.
> >> >> You've never had to do it even once because bean counters don't do
> >> >> design. Never have, don't now, and never will.
> >> >IMHO,
> >> Your 'opinion', and following gibberish, is twaddle. It may fool
> >> fellow ignorants who, like you, haven't a clue but it's drivel to
> >> those of us who've worked with your so called 'bean counters' and done
> >> professional product design.
> >> I don't speak from 'opinion' and cartoons. I speak from fact, having
> >> been there and done that.
> >Its OK, every man's facts are another man's fictions, and one man's
> >trash is another man's treasure.
>
> More gibberish. Go bang your head on a wall and see how far you get
> wishing it were 'fiction' rather than solid fact.
>
> >I just see lots of what I don't want to buy or approve of or want to
> >be involved in and if everyone was like me the world would collapse.
> >But fear not and be grateful for the human diversity around you now.
>
> It should be blindingly obvious by now that you are not representative
> of the market.

Irelevant.
>
> Of course, it's also blindingly obvious that accountants are trained
> in accounting, which is pretty much why they're called accountants,
> and not design but, then, it being obvious to everyone else has never
> stopped your delusions yet.
>
> *It's true that more robust construction would have made these things
> last longer, but to be fair, no one realistically figured anyone would
> be running these things fifty or sixty years hence.

And all the old junk needs serious care and revisions to rectify bean
counter inspired shortcomings.

> *Saul Marantz (yes, I know) was determined to make the finest quality
> hi-fi equipment and spared little in the quest to do so. His build
> cost was double and then some of what his nearest competitor,
> McIntosh, spent per unit.

I've never wanted anything made by Marantz, could always have been a
lot better.
>
> *Avery Fisher (yes, he was too) was more mainstream but still put a
> lot of build cost in his product as compared to his competitors.

Ha, most of the Fisher stuff is generic junk. I've had to repair,
modifiy, re-do, undo bad ways all these brands used to save a dime.
>
> *Both businesses are out of business in terms of being an American
> manufacturer. McIntosh is also owned by Japanese, BUT are allowed to
> operate autonomously and they are still manufacturing in Binghamton.

And of course the OWNERS exert hard financial controls over design.

I've worked on the McIntosh re-issue models they sell here for $4,300.
REAL CRAP. pcb boards all miniturised, hard to work on short cuts
from the old circuits, tube biasing up to ****, bean counter inspired.


But really, I raise my hat and salute all bean counters for destroying
product quality while jacking up the price because I can compete with
their dumbed down over priced garbage.

Henry Ford raised his hat whenever he saw a Fiat drive past, or a
Morris, or an Alfa Romeo not to mention a Rolls or a Merc.
Not that I'm like Henry, but the urge to smile and raise a hat is the
same.

Maybe Henry would not have raised a hat if he'd seen a Toyota drive
past :-)

Dammit, we beat Japan and now they come back at us! The damn Gummint
musta betrayed us! Tough titty, buster, the people really want the
best cheap car.


>
> *We can look at the classic Mac products and say there were several
> aspects where they could have done better but the salient fact is,,
> they are still here.

Just being here counts for nothing.
>
> *Quad never set out to be the technical ulimate but to be a usable
> integrated system and they succeeded marvelously.

Indeed they tried something. Quad tubed AM tuners, and ESL57 were
good, but everything else MEDIOCRE, ain't nothin special, just chic
junk, like Bose Lifestyle systems and B&O is now. You should see the
BO-6002 slimline speakers I have here for repair, and how badly they
have failed, utter CRAP.

I was never conned by ticky tacky accountant inspired crap where
construction costs were pushed down and down thus smothering technical
integrity.
>
> *Even the Dynaco ST70, which I have slammed long and hard, has to be
> admitted as having been insanely successful in its day.

Desperate ppl by the cheapest muck they can, so they bought Dyanco
ST70.

Not many bought Mk VI monoblocks. Now these did have more merit, but
SO MUCH can be done to vastly improve them if the whole circuit is
junked then you just use the chassis, PT and OPT.

But I find bulldozing all the old crap out and starting all over
applies to each and every US made amp I have ever seen enter my shed
because the owners hated the smoke and were none too keen about the
sound. ARC, Manley Labs, Dynaco, VAC, Fisher, Pilot, and many more.
All designed with cost minimisation in mind.

> standards of its day it was a great product because a college kid
> could afford a Dyna pre and ST70, and AR table and an AR acoustic
> suspension speaker set in 1963. Some portable record player outfits
> cost nearly as much. Again, no one realistically thought thay would be
> running in 2011.

Yes, sure, but right out of the factory, a lotta the old junk your so
proud of was crap because it was already dumbed down by cost cutting.

Its going on today with a whole pile of consumer gear, you buy it, it
breaks, and you chuck it out, because the cost of a repair is larger
than the replacement price, and not to mention that stuff becomes
obsolete, like PC boxes which we all thought were cool in 1995. Its
rubbish now.

AR speakers have very limited appeal for me. Their Flagship model in
1975 was the AR9, and I've had the true displeasure of spending weeks
to make them right. They were $4,500 in Oz in 1975, or in today's
dollars, $90,000. But what was inside? Utter generic crap and
attrociously worst lowest common denominator R, C and L and speaker
drivers. I've measured mint pairs of AR9 and found the response
nothing like what the brochure says. The paralleled 11" bass speakers
have 1.5 ohms impedance at critical bass F and ppl who buy such
speakers want loud bass but they'd blow up amps real well. The AR bass
drivers are probably the most insensitive bass speakers I have ever
measured. The crossover design is hopeless ly inadequate. Basically
AR9 should have sold for $45 in 1975, not $4,500, ie, $900 in todays
dollars.
So my conclusion about AR was that they had very poor management, very
poor quality control, accountants who were ac****ants, a workforce of
rushed and cheap dumbos with minimum skills, and engineers who knew
jack ****.

But they had the best promotions staffers in the world, the best
liars, and maybe they employed the best advertizing company. They
speaker building efforts were just an entrenerial exercize, like so
many other crappy things made around the world in 1975. It was so easy
to study a book or two and make your own speakers that would then cost
$200 which would easily beat the AR9 for $4,500. I did just that. I
baulked at building tube amps in 1975, too many other things in life
to do but I bought a Linear Design receiver in 1977 for $200, less
than half the price and better sounding that the equivalent Marantz
rip off. I still have that receiver.

>
> *Had the dyna been "built right" it would have had to cost more, maybe
> considerably more.

The CEO then could not have afforded a Cadillac. Ah, the wonders of
capitalisic greed!


> One area where they shaved was weight to meat a
> Railway Express shipping target. That's why the power transformer is
> undersize. The profit *margins in this stuff were minimal.

Total ****in bull**** type stuff.


>
> *It's like a car. Yeah, if ALL the Ford Mustangs had had 9 inch rears,
> five bolt disc brake setups and so forth they'd have been better cars,
> but 90% of them were going to the crusher in five or six years anyway.
> If they had overbuilt them it would have made little difference in
> this rate. A great many cars get driven to the crusher under their own
> power.- Hide quoted text -

Well thank christ most old US made cars have been recycled so that 2
cars come from the metal used for one. We have a big car festival here
each summer, see http://www.summernats.com.au/ The grounds are just
1/2 a km away from where I live. But I just don't see what the
thousands or rev-heads see in their cars which are expensive, noisy,
and a waste of money, like the rich men's yachts at Pit****er. All
this stuff, more stuff, no end to stuff, more and more horse power and
much of it crap. So Vain! So Futile, So Meaningless. So Wasteful. So
Unsuccessful. I've seen the work guys put into cars, beautiful sure,
but heck, its only a car, and how come it don't give 50MPG? How come
most of the hotted up highly modified cars are NOT allowed on city
streets but are confined to the show ground parade loop? Because so
many dreadful incidents occurred when the rev-heads were allowed to
drive on city streets. Strict Government control is needed. But 5,000
people manage to have a ball for 4 days and maybe spend a grand or two
each. But far more income comes from big art shows at the National
Gallery. Just harmless paintings on the wall, no smoke, burnt rubber,
stoopid young jerks showing off and wasting so much precious fuel.

Its most unfortunate that American cars have wasted so much fuel
because bean counters stopped expense on developing efficiency; better
to lobby the Govt about 101 favours and do all sorts of weird deals so
that Joe Public funds the inefficiency, not Ford, Not GM, Not Chrysler
or anyone else except Jack Buyer. Yippee, 7 litre engines and 10MPG,
WOW, what progress to be proud of, I DON'T THINK! Ralph Nader should
not have had anything to write about, but he did, and you ought to
know that.

A country and its people should never rest on its laurels, never self
congratulate itself, and when the accountants and the bankers go to
lunch for 3 hours every day you know things are close to ****ed.

The GFC was a sure indicator of that.

Maybe the US will muddle along out of its woes, but there's a long way
to go, and youse will have to learn fast to reduce greenhouse CO2 just
when ya don't wanna pay, while mostly denying any problem even exists.
America seems like the fat guy who is told the doc won't operate
because he's so fat, and the guy says he really wants that operation
but he can't stop eating so much. America shows what the rest of the
world should not want to copy or emulate. And in countries like mine
which has addopted much of the excessiveness and greed and bull****,
the carbon tax is a raging argument and people don't want to pay for
the change necessary to keep the planet cool. Some will pay more than
others, and as usual a whole big argument is on over that one, so
muddle here is as big as muddle where you are and elsewhere. Muddle is
normal. We never get over it, and I doubt you can admit you are a
member of a seriously flawed species. Never mind, you will die with
your beliefs like those who clung to the idea that the Earth was flat
even on their death bed. The grave will take stubborn beliefs with the
man, and the enligtened will inherit the Earth, and the job of energy
management revolution will be done by young clever hands and minds who
criticise themselves and methods each and every day, not to save a
dime while charging outrageous prices. And the product of the
revolution for the next 50 years might give us time to avoid the silly
wars we've had, and the absurd way we treat forests, and environment.
I'd like to think the coming revolution might allow some frivolity
like the occasional tube amp but never again will mainstream stuff be
allowed to be as bad as it was in 1950. PWM amps are very efficient, a
bean counter's delight in fact, don't even need a heatsink. Tiny robot
made circuitry allows highspeed switching signals. Chinese labour
ruins any chance of the US charging too much like they used to. Not a
perfect scene because the average Chinese worker gets shafted, but his
64c an hour is better than 20c per hour on the farm up the country
where his parents eek out a living that is infinitely unacceptable to
the average Oz or US person. The failure of the Chinese for 3,000
years has been to not improve life much for themselves, and the
failure of the West has been to improve its material wealth far too
much while swanning around and crowing about how wonderful it is. I
don't care if I represent the minority view of things in general.

Patrick Turner.

[Patrick Turner]

On May 31, 2:51*pm, Bret Ludwig > wrote:
> > So where were you when ya could have lent them your machine gun to
> > make Britain a better place?
>
> > Oh, I guess you really hate all those Mexicans crossing the border
> > too, yet they do all the dirty work so nice and cheap now don't they?
>
> > Probably you hate a browned skin man being President Of the USA, and
> > giving speaches in Ireland last week which would have been totally
> > beyond the capability of Dubbya, or of Sarah Palin.
>
> *I preferred Obama to McCain in fact as did most WNs. He has been a
> disappointment to be sure but any other candidate would have been as
> well who would have been likely to have been nominated.

Well, Obama means well, IMHO. If Sarah joins the race, I doubt she'd
got a chance. Maybe the best Republicans are still mending fences
after the GFC.

>
> *I don't hate the Mexicans, although I acknowledge that the Mexicans
> coming here are mostly the browner and stupider ones who can't make it
> back home.

But that's what so many say about "boat people" from Ghan and Iraq
coming here "illegally" But they are clever enough to make enough
money to pay ppl smugglers and get here.

> I detest the fact that our politicians won't do what any
> nation has to do which is secure its borders and throw out violators.

That's what a lot of Indians said about the white man invading their
lands. Our aboriginies resented the White man coming here in boats,
unwanted, and uninvited, and after they settled they practised
genocide.

> The Republicans want cheap labor to undercut the American worker, both
> black and white, and the Dems want the illegals to vote, and vote
> Democratic, which they will.

Ya can't have it both ways. Money wins, no, so illegals will stay to
do work the White Fella won't. Count your blessings you don't have to
work in a food processing factory at 50C all day with quotas to meet
and low pay so your vegetables are cheap for you.
>
> *Machine gunning people is not the answer.

Well of course not. Far too messy. I didn't mean what I said, just
jesting.
Fooling people to take up residence in places with signs which say
Work Makes You Free would be easier, and you pop a little gas in while
they have a shower before work, and then you cremate them. But you'll
get spotted, some upstart will upload a mobile phone pic of the Zyclon
B gas tablets to Facebook and the Feds will come straight over. Nah,
extermination just won't work. Far better to fudge. Appear to be
taking action, but somehow brownskins increase anyway. The Whites have
remarkably low birthrates, and half end up on welfare too soon.


> Enforcing the law firmly
> and acknowledging that we are White countries who should and must stay
> that way is.

Yeah, but youse being out ****ed and thus out bred by Brownies, happy
smiling millions of 'em, God Love 'em. People here wanted Oz to stay
all White, and they brought in a White Australia Policy before WW1.
After WW2 It hit the dust as one of the most obnoxious, unworkable
stupid political ideas we ever came up with. After WW2 we let in all
these garlic eating wogs from Italy, Germany, Holland, Greece, and
WHOOPPEE!!! the party began, wealth went everywhere except down, these
wogs were fabulous new blood. After 1978, 200,000 Vietnamese came in.
WOW. Now we have some of the worlds best medicos.

> No one race is "superior", but we are who we are and
> should stay that way. *Britain should be for the British and America
> for the Americans.

Total unmitigated uneducated bull****! Also ********. Definate
Balderdash. Even if you tried, the US cannot remain as you'd wish it,
which is the product of much immigration and the overcoming of huge
intolerances of differences. One most hated group of Whites were Jews.
But once in America they have flourished to enrich our lives far more
than they impoverished lives.

Plenty of brown skins here. No troubles, taxis come on time and driven
by Pakistanis. Indians grow the best tea to drink. Hospitals run
finely with asians everywhere. I love them all. I go to a cafe across
town, one of 3 in a row in a main street of a town center. Its the
Istanbul, run by arabs, but on a sunday they only get 1/3 of the
patronage of the joint next door which charges more but is run by
Whites, with mainly white customers who mistakenly might think Arabs
suck, and especially Islamic culture. So prejudice remains, but is
still breaking down and the arabs will blend in a generation and Islam
fades to relative unimportance and the whole becomes homogenous and
Whites slowly appreciate what the arabs bring. It was the arabs who
brought coffee to the west in the first place. And before that we sent
the crusades to butcher them. Its amazing so few Islamic extremists
like Arsole Bin Laden have come to spoil the party we've been having
at the expense of brown skin exploitation by Whites. We have a White
Woman as our dear leader and she's having dreadful trouble dealing
with horrible untidy unwashed brown illegals, and she plans to do all
sorts of inhumane things to them. She's also having frightful trouble
getting ppl to believe in her Carbon Tax. Now just where is a good
strong fit brown man who can be a good leader when you want one?

Look, if Sarah makes it to the White House, send Obie down to us, we
need a man like that. And we might have learnt to let him in by then.

Patrick Turner.

[Patrick Turner]

On May 31, 1:09*pm, John Byrns > wrote:
> In article >,
> *Patrick Turner > wrote:
>
>
>
>
>
> > On May 29, 11:23*am, John Byrns > wrote:
> > > In article >,
> > > *John L Stewart > wrote:
>
> > > > Before this thread went off the rails did anyone mention that McIntosh
> > > > uses a seperate winding on the OPT for overall NFB?
>
> > > A separate winding, a tertiary winding, provides better high frequency
> > > stability
> > > than taking the NFB from the secondary winding. *The down side of using a
> > > tertiary winding for NFB is that the NFB doesn't include the secondary so
> > > that
> > > the damping factor suffers, this probably has no practical consequence, but
> > > doesn't make for good ad copy.
>
> > Yes but the NFB winding position relative to anode turns or secondary
> > turns will have an effect on what is fed back.
>
> Yes, the design/positioning of the tertiary winding affects the leakage
> inductances between the various windings
>
> > I'd say that if a fine wire NFB winding is wound right over the top of
> > a thick wire speaker secondary then its signal is near equal to the
> > speaker's signal and the "error" made by the secondary Rw and LL and
> > phase shift et all is fed back for correction.
>
> No tertiary can correct for the "Rw" of the secondary!

I'm not so sure. if the tertiary is wound close to anode coils, sure,
Sec Rw is not reduced by NFB. But if tertiary is wound close to Sec, a
drop in sec voltage gives a drop in tertiary voltage, and a FB signal
corrects the drop, no?

,
>
>
>
>
>
> > But if the FB tertiary is next to the anode primary then you have a
> > good hum free FB source with anode signal without LL and Sec Rw
> > effects and the amp is MUCH easier to stabilise unconditionally. Such
> > a low voltage and grounded winding gives a conveniently small FB
> > signal with low source resistance which can be applied to an earlier
> > stage very effectively. Such a signal picks up a sample of the whole
> > Va-a, and is a better NFB than using a cap plus R divider from one of
> > the PP anodes back to an input tube cathode. But bean counters mostly
> > hated paying for a dedicated NFB tertiary. Why have one when the
> > speaker secondary exists? Indeed why have one? if you make the OPT
> > with sufficient interleaving then the Williamson way of NFB is fine,
> > but bean counters hated Williamson too, and laughed at what he said
> > makers should do, so we all mainly ended up with OPT with very high LL
> > and appalling stability problems.
>
> > > Marantz used an interesting NFB scheme that took the NFB from the secondary
> > > at
> > > low frequencies to provide a good damping factor and then used a crossover
> > > filter to take the high frequency NFB from tertiary windings.
>
> > I'm not sure about that one. Some makers just used the speaker sec for
> > normal global NFB with R divider to feed V1 cathode but then the cap
> > that is normally strapped across the FB R to advance the phase of the
> > fed back signal at HF is not used, but a cap from V1 cathode is taken
> > to one of the OP tube anodes. I've always found no real joy in such
> > measures and I prefer the normal conventional Williamson idea where
> > one makes the OPT have wide BW which then pushes the regions where
> > instabilty occurs further below and above the AF band and thus to
> > where its easy to instal gain reducing and phase tailoring networks
> > while maintaining 10Hz to 65kHz full power bandwidth with complete
> > stability and 20dB global NFB is desired. I'll follow the Williamson
> > principles before I'll follow any others. I happen to like using
> > tertiary windings for NFB myself, but in the form of CFB windings
> > which are a part of the OPT primary and which carry Ia. Its the
> > Acoustical. Thus the OP stage is substantially linearised and given
> > the character of triode Ra and low THD while retaining the tertrode
> > AB1 or A1 power. Then only 10dB of global NFB is needed, if any at
> > all.
>
> CFB is nice, but it does increase the demands on the driver stage substantially.

Depends how much CFB. Mcintosh amps need a max 150Vrms to 6550 output
tube grids for clipping. So the THD of the driver stage tugs at the
gains of so much CFB ( 50% ) in the OP stage.

Quad-II only have 10% CFB, and the KT66 are about as sensitive as a
50% UL stage. But the 10% CFB is more effective in getting Ra-a to the
same level as triodes. A 50% UL stage gives Ra-a about = to RLa-a,
several times the Ra-a of triode, broadly speaking.

I like 20% CFB, drive voltage goes to about 75Vrms to each 6550 grid
and I then build the drive amp to make far less THD than anything by
McIntosh or Quad, and voila, very low THD with very little global
NFB.

Patrick Turner.

d a
>
> --
> Regards,
>
> John Byrns
>
> Surf my web pages at, *http://fmamradios.com/- Hide quoted text -
>
> - Show quoted text -- Hide quoted text -
>
> - Show quoted text -

[Patrick Turner]

On May 31, 1:06*pm, John Byrns > wrote:
> In article >,
> *Patrick Turner > wrote:
>
> > On May 29, 3:47*am, John Byrns > wrote:
> > > In article
> > > >,
> > > *Patrick Turner > wrote:
>
> > Well, I can't explain it any better than I have. If circuit gain is
> > increased by feeding back a fraction of an output signal of one stage
> > to an earlier stage and the gain is increased, THD increased,
> > bandwidth reduced, then I'd say PFB exists. We see feathers, a ducks
> > bill, wings and webbed feet, a ducks tail that wags and we say there's
> > a duck.
>
> Unfortunately this is a completely incorrect description of how a generic
> paraphase inverter operates, so the duck analogy doesn't apply.

Oh well, I can agree to dissagree
>
> > > > The concertina "throws away" most of its gain so that +19Vin to a 6SN7
> > > > produces -17Va and +17Vk, with the +2Vgk needed to make the total
> > > > 34Vak output, so open loop gain = 17, but closed loop gain is 34 / 19
> > > > = 1.79, and this has beautiful low THD because the 19dB current NFB
> > > > present.
>
> > > So the concertina requires 1.12 Volts in for the specified 34V grid to grid
> > > output drive vs. 1.0 Volts in for the paraphase and 2.0 Volts in for the
> > > LTP. *
> > > 1.12 Volts is close enough to 1.0 Volts for Government work, at least it is
> > > a
> > > lot closer to 1.0 Volts than it is to 2.0 Volts.
>
> > The paraphase tends to add gain "artificially" for a given number of
> > tubes, moreso than merely cascading them.
>
> "artificial" gain is the best kind, it can be made so pure that its sound is
> simply sublime.

If only it was true. Paraphase and PFB usually have higher than
possible THD without the paraphase PFB. The sound of such stages
cannot be assumed to be sublime, and wherever higher THD is allowed to
breed unecessarily the sound drifts to mud.
>
> > And in the case of Quad-II, the KT66 grids are biased via 680k Rgs,
> > and one has a 2k7 at its bottom from which the signal to V2 pentode
> > grid is wrought.
> > Now that 2k7 is just what Walker chose, but it could be a range of
> > values; if larger, there's more PFB and more gain and weird things
> > happen when you increase that
> > 2k7 too much because there is a definite limit to the amount of PFB
> > which can be applied without terrible instability.
>
> I don't know if 2k7 is the correct value for this resistor, I assume that Quad
> choose correctly here, there is only one correct value for this resistor where
> the circuit will function properly, other values are not an option! *

Don't be so sure about this. Try building an input stage identical to
Quad-II in some amp you have laying around. You don't need pentodes; a
single 12AX7 will do, and where the Quad has 680k plus 2k7 try putting
a 5k pot to replace the 2k7, then add some NFB and make some
adjustments with the pot. After awhile the penny drops about the PFB,
too much is hell, just enough is all that's needed - about 6dB.
You'll soon find that probably optimal R value is where there is
minimum signal voltage across the 680 ohm common Rk to the two EF86,
or 1/2 12AX7, so the trick of the circuit is that the EF86 tend to
have a fake CCS connected to common cathodes. One may analyse the
effects of a distortion signal fed back along the signal path and what
happens to it in terms of gain. But the PFB increases the amount of
NFB applied beyond what it appears to be. There is more to Quad-II
input drive amp than 90% of people may realise.


> Changing
> the value of this resistor will change the amount of PFB as you say, thereby
> changing the gain of V1. *The problem with changing the value of this resistor
> away from the correct value, to some other value, is that in addition to
> changing the amount of PFB, it also unbalances the phase inverter so that the
> two output tubes don't receive the same amount of drive voltage.

Very few Quad-II amps have well balanced drive. But I recall the 2k7
was not critical for balance. I suggest you try examining a Quad-II
circuit.
What I can say is that a pair of EF86 set up as a TRUE LTP with
existing load values, but with large R value for common Rk taken to a
rail at -400Vdc, and NFB applied to V2 EF86 grid, then the drive amp
produces 1/2 the THD as the original Quad-II circuit. But sensitivity
halves and twice the grid 1 input signal is needed. Quad couldn't push
pentode gain higher so they needed the trick thay have used. Quad
didn't think of a way to bootstrap the RL of each pentode anode to
increase gain. That would have needed a twin triode for a pair of µ
followers in a balanced pair but the balance of such pairs is poor
because so little signal Ia exists and balance in LTPs depends of R
load equality.

The better way is to use an SET input triode followed by low µ twin
triode for LTP, 12AU7, 6CG7 is ideal. or have LTP input with 12AU7 and
CCS tail followed by balanced amp with long common R tail to -120Vdc;
methinks this is the king of input/driver stages for PP.

> > Next time you play around with a paraphase stage, try tinkering with R
> > diver values and drive from V1 to V2. Interesting stuff happens, with
> > not much of it of real value.
>
> What exactly are "R diver values"? *There is only one correct value for the
> "drive from V1 to V2", you may find other amounts of drive interesting, I'm not
> sure why though?

Divider values. Nobody dives anywhere. 680k and 2k7 give Quad's wanted
signal for V2 grid, and you can't guess the voltages.

Patrick Turner.
>
> --
> Regards,
>
> John Byrns
>
> Surf my web pages at, *http://fmamradios.com/

[John Byrns]

In article >,
Patrick Turner > wrote:

> On May 31, 1:06*pm, John Byrns > wrote:
> > In article
> > >,
> > *Patrick Turner > wrote:
> >
> > > Well, I can't explain it any better than I have. If circuit gain is
> > > increased by feeding back a fraction of an output signal of one stage
> > > to an earlier stage and the gain is increased, THD increased,
> > > bandwidth reduced, then I'd say PFB exists. We see feathers, a ducks
> > > bill, wings and webbed feet, a ducks tail that wags and we say there's
> > > a duck.
> >
> > Unfortunately this is a completely incorrect description of how a generic
> > paraphase inverter operates, so the duck analogy doesn't apply.
>
> Oh well, I can agree to dissagree

The point is that only one variant of the paraphase inverter circuit, the one
where V1 & V2 share an unbypassed common cathode resistor, as used in the QUAD
II, has the PFB you describe, the generic paraphase inverter and other variants
don't have the PFB you are talking about.

For example, take a look at this paraphase inverter circuit.

http://hhscott.com/pdf/250.pdf

Where is the PFB in this circuit? The 6 dB gain increase exists even though
there is no PFB in this circuit. The 6 dB gain increase is simply the result
adding the voltage mirror stage which doubles the total output signal, this is
typical of all paraphase inverter circuits.

The PFB in the QUAD II circuit can be eliminated by tying a large electrolytic
capacitor from ground to the common cathode of V1 & V2, the gain of the inverter
circuit will not change when the PFB is eliminated this way, although there will
be a problem applying global NFB with the capacitor in place. If you try this
experiment with a capacitor from ground to the common cathode of V1 & V2, be
sure and disconnect the global NFB first by disconnecting the 470 Ohm NFB
resistor from the secondary of the OPT and connecting it to ground before making
any measurements.

> > > The paraphase tends to add gain "artificially" for a given number of
> > > tubes, moreso than merely cascading them.
> >
> > "artificial" gain is the best kind, it can be made so pure that its sound
> > is
> > simply sublime.
>
> If only it was true. Paraphase and PFB usually have higher than
> possible THD without the paraphase PFB. The sound of such stages
> cannot be assumed to be sublime, and wherever higher THD is allowed to
> breed unecessarily the sound drifts to mud.

It is as true as calling the 6 dB gain of the paraphase inverter "artificial",
when it is actually a direct result of adding the voltage mirror circuit.

> > > And in the case of Quad-II, the KT66 grids are biased via 680k Rgs,
> > > and one has a 2k7 at its bottom from which the signal to V2 pentode
> > > grid is wrought.
> > > Now that 2k7 is just what Walker chose, but it could be a range of
> > > values; if larger, there's more PFB and more gain and weird things
> > > happen when you increase that
> > > 2k7 too much because there is a definite limit to the amount of PFB
> > > which can be applied without terrible instability.
> >
> > I don't know if 2k7 is the correct value for this resistor, I assume that
> > Quad
> > choose correctly here, there is only one correct value for this resistor
> > where
> > the circuit will function properly, other values are not an option! *
>
> Don't be so sure about this. Try building an input stage identical to
> Quad-II in some amp you have laying around. You don't need pentodes; a
> single 12AX7 will do, and where the Quad has 680k plus 2k7 try putting
> a 5k pot to replace the 2k7, then add some NFB and make some
> adjustments with the pot. After awhile the penny drops about the PFB,
> too much is hell, just enough is all that's needed - about 6dB.
> You'll soon find that probably optimal R value is where there is
> minimum signal voltage across the 680 ohm common Rk to the two EF86,
> or 1/2 12AX7, so the trick of the circuit is that the EF86 tend to
> have a fake CCS connected to common cathodes. One may analyse the
> effects of a distortion signal fed back along the signal path and what
> happens to it in terms of gain. But the PFB increases the amount of
> NFB applied beyond what it appears to be. There is more to Quad-II
> input drive amp than 90% of people may realise.

You need to be a little more definite about what this faux QUAD II phase
inverter circuit using 12AX7s is supposed to look like? Is it just to be an
input stage without any global NFB? Assuming that we aren't worrying about the
complex provisions for global NFB in the QUAD circuit, having omitted them, it
is obvious by inspection that when the "R value" is adjusted for equal outputs
from the two plates of the inverter circuit, then the signal voltage on the
common cathodes will be minimized. Adding the QUAD style global negative feed
back circuit greatly complicates things, as global NFB is applied to V1 and both
global NFB and global PFB are applied to V2.

I don't think I would say "that the EF86 tend to have a fake CCS connected to
common cathodes", if anything I would call it a "fake piece of wire".

The QUAD II input stage has much more going on in it, at multiple levels, than
you seem realize, or seem have thought about. I'm not saying that your Turner
circuit isn't better, however you should have made an effort to more fully
understand the operation of the QUAD input circuit before ripping it out and
replacing it with your design.

> > Changing
> > the value of this resistor will change the amount of PFB as you say,
> > thereby
> > changing the gain of V1. *The problem with changing the value of this
> > resistor
> > away from the correct value, to some other value, is that in addition to
> > changing the amount of PFB, it also unbalances the phase inverter so that
> > the
> > two output tubes don't receive the same amount of drive voltage.
>
> Very few Quad-II amps have well balanced drive. But I recall the 2k7
> was not critical for balance. I suggest you try examining a Quad-II
> circuit.

I have examined the QUAD II circuit, and did so long before you were even aware
of its existence, if some of your narrative here is to be believed. The 2k7 is
absolutely critical for proper balance in the QUAD II, however balance is also
dependent on the gain of V2 in addition to the value of the 2k7. I suspect that
the reason QUAD didn't use a self balancing type of paraphase circuit in the
QUAD II is because it would have required more components, including at least
one electrolytic capacitor for the cathode of V1 to maintain gain, and there
would have been a slight loss in open loop gain, less than 1.0 dB, due to
increased loading on the driver plates, and there is little doubt that QUAD was
pinching pennies in the QUAD II, so the increased cost, and very slight loss of
gain would have been intolerable.

--
Regards,

John Byrns

Surf my web pages at, http://fmamradios.com/

[John Byrns]

In article >,
Patrick Turner > wrote:

> On May 31, 1:09*pm, John Byrns > wrote:
> > In article
> > >,
> > *Patrick Turner > wrote:
> >
> > > On May 29, 11:23*am, John Byrns > wrote:
> > > > In article >,
> > > > *John L Stewart > wrote:
> >
> > > > > Before this thread went off the rails did anyone mention that
> > > > > McIntosh
> > > > > uses a seperate winding on the OPT for overall NFB?
> >
> > > > A separate winding, a tertiary winding, provides better high frequency
> > > > stability
> > > > than taking the NFB from the secondary winding. *The down side of using
> > > > a
> > > > tertiary winding for NFB is that the NFB doesn't include the secondary
> > > > so
> > > > that
> > > > the damping factor suffers, this probably has no practical consequence,
> > > > but
> > > > doesn't make for good ad copy.
> >
> > > Yes but the NFB winding position relative to anode turns or secondary
> > > turns will have an effect on what is fed back.
> >
> > Yes, the design/positioning of the tertiary winding affects the leakage
> > inductances between the various windings
> >
> > > I'd say that if a fine wire NFB winding is wound right over the top of
> > > a thick wire speaker secondary then its signal is near equal to the
> > > speaker's signal and the "error" made by the secondary Rw and LL and
> > > phase shift et all is fed back for correction.
> >
> > No tertiary can correct for the "Rw" of the secondary!
>
> I'm not so sure. if the tertiary is wound close to anode coils, sure,
> Sec Rw is not reduced by NFB. But if tertiary is wound close to Sec, a
> drop in sec voltage gives a drop in tertiary voltage, and a FB signal
> corrects the drop, no?

NO, even if the tertiary were perfectly coupled to the secondary, it still
couldn't compensate for the secondary winding resistance.

--
Regards,

John Byrns

Surf my web pages at, http://fmamradios.com/

[Bret Ludwig[_2_]]

>
> > *Saul Marantz (yes, I know) was determined to make the finest quality
> > hi-fi equipment and spared little in the quest to do so. His build
> > cost was double and then some of what his nearest competitor,
> > McIntosh, spent per unit.
>
> I've never wanted anything made by Marantz, could always have been a
> lot better.


Have you ever seen a marantz 2, 5 or 8B amplifier or a 9 or 9C
preamp???????????


I don't think they ever sold them in Australia.

Maybe you are unaware that before the Japanese bought them they were
US made and quite expensive.

The reissue Mc 275s are not very good as compared to the originals
except for the chassis.

[Bret Ludwig[_2_]]

So prejudice remains, but is
> still breaking down and the arabs will blend in a generation and Islam
> fades to relative unimportance and the whole becomes homogenous and
> Whites slowly appreciate what the arabs bring. It was the arabs who
> brought coffee to the west in the first place. And before that we sent
> the crusades to butcher them. Its amazing so few Islamic extremists
> like Arsole Bin Laden have come to spoil the party we've been having
> at the expense of brown skin exploitation by Whites. We have a White
> Woman as our dear leader and she's having dreadful trouble dealing
> with horrible untidy unwashed brown illegals, and she plans to do all
> sorts of inhumane things to them. She's also having frightful trouble
> getting ppl to believe in her Carbon Tax. Now just where is a good
> strong fit brown man who can be a good leader when you want one?
>

5000 years of history calls bull**** on this. You'd be smart to boot
all nonwhites except for the abbos and put them in a nice, safe fenced
off area where they can live as they always have with NO CONTACT with
the whites. Leave them alone as if whites never came so people can see
what 50,000 years of progress is for a 55 IQ race. And shoot any
white who ****s one. Race mixing equals death for any people.

[John Byrns]

In article >,
Bret Ludwig > wrote:

> >
> > > *Saul Marantz (yes, I know) was determined to make the finest quality
> > > hi-fi equipment and spared little in the quest to do so. His build
> > > cost was double and then some of what his nearest competitor,
> > > McIntosh, spent per unit.
> >
> > I've never wanted anything made by Marantz, could always have been a
> > lot better.
>
>
> Have you ever seen a marantz 2, 5 or 8B amplifier or a 9 or 9C
> preamp???????????

I owned a Marantz 8B in the day, I would have thought it would have received
high marks from Patrick, at least as high he would give any commercial product.
It even uses the sort of circuit he espouses, I'm not sure if the OPT would be
up to his standards though.

I never heard of the Marantz 9 or 9C?

--
Regards,

John Byrns

Surf my web pages at, http://fmamradios.com/

[Patrick Turner]

On Jun 2, 12:00*am, John Byrns > wrote:
> In article >,
> *Bret Ludwig > wrote:
>
>
>
> > > > *Saul Marantz (yes, I know) was determined to make the finest quality
> > > > hi-fi equipment and spared little in the quest to do so. His build
> > > > cost was double and then some of what his nearest competitor,
> > > > McIntosh, spent per unit.
>
> > > I've never wanted anything made by Marantz, could always have been a
> > > lot better.
>
> > *Have you ever seen a marantz 2, 5 or 8B amplifier or a 9 or 9C
> > preamp???????????
>
> I owned a Marantz 8B in the day, I would have thought it would have received
> high marks from Patrick, at least as high he would give any commercial product. *
> It even uses the sort of circuit he espouses, I'm not sure if the OPT would be
> up to his standards though.
>
> I never heard of the Marantz 9 or 9C?
>
> --
> Regards,
>
> John Byrns
>
> Surf my web pages at, *http://fmamradios.com/

I had a look at all Marantz models 5 to 9.

They do look well on paper with a 6BH6 ( like a 6AU6 ) in triode for
V1, then a 6CG7 direct coupled LTP like Mullard does, with EL34
outputs in UL. Not too many problems with all that but the anode
loads for 6CG7 are way too low, and consist of 5k pot for AC
balancing.with 15k to each anode when it really should be 47k The
obvious mod to make it all work better is to have CR coupling from V1
SET 6BH6 to one 6CG7 grid biased for 0V, then have the other grid
grounded, then have a negative rail of say -200Vdc to -400Vdc for the
common Rk, and then get the B+ to be higher and then you have 6CG7 Ea
and Ia higher with RL higher and maybe the THD of the stage is much
reduced. A CCS LTP tail taken to say -50V would be best though because
the pot for AC balance can be omitted if the RL for each anode is
equal which is easy to do these days.

The Marantz OPT takes most of its LF NFB from the 4 ohm tap on the
sec. But there is an additional NFB winding with its live end connectd
to the 16 ohm tap via 10 ohms, and the NFB winding feeds HF NFB to the
V1 cathode via 1.2nF. I'd guess the NFB winding does not experience
the same phase shift caused by LL and the load at HF, so Marantz
manages to apply NFB over a wide BW without trying to fix the phase
lag at HF. But without having a Marantz here to examine, I cannot say
exactly how well the arrangement works, or understand exactly how
Marantz wound its OPTs. How can I endorse something I have never
examined properly? Impossible. But if Marantz had used a 5P x 4S
interleaving pattern with 6 secondary sections each for 16, 8 &4 ohms
and all paralleled, there would have been no need for a NFB winding
because such interleaving with paralleled secs give wide BW for this
sort of amplifier as Williamson and McIntosh have so so clearly
established over the last 60 years. Tapped secondaries usually have
higher winding resistance than where 4 sec sections are strapped in
different patterns for the load match variations. Most manufactuers
have used appallingly thin wire in OPT secs and rarely ever have 4 Sec
sections; two if you are lucky, and often the two will each be a match
for 4 ohms, so that the two series S sections give 16 ohms, a tap
along one section gives 8 ohms, and only one section is then used for
the 4 ohm match and it is with 4 ohms that there is the highest LL and
worst BW and highest instability and highest winding losses. As i
said, for good performance for a 50W OPT, you'll need 5P x 4S, and
each Sec section should be a match for 16 and so with 4 ohms you still
have 5P x 4S interleaving, even though 1/2 the sec turns are unused.
The strapped method of changing Z match on OPTs is often done poorly.
For example, in Quad-II there are only two link changes needed for 8
or 16 ohms, but no official match for 4 ohms. Walker must have
pondered how to set up the OPT and its strapping method long and hard
to satisfy a Nation Full of Dumbos who are confused if forced to count
beyond 3. Quad-II would be a MUCH better amp if it were possible to
strap all OPT secs to get a wasteless arrangement of secs so that
every length of secondary wire had the same current density.
Then the Quad-II would have allowed a P-S load match of 4k0 : 4 ohms
which would better suit most modern LS, and of course using 8 ohms on
the 4 ohm outlet gives 8k0 : 8 ohms and nearly all class A which suits
the old junk circuit best. See why I say old junk is OLD JUNK?
Its because I can see that the old gizas who designed all that old
junk *could* have made masterpeices with an extra 2 hour's thought and
4 hour's more labour. But alas, the designers were addicted to
mediocrity.

One more thought about LTPs.

I find LTP with CCS cathode tail and high RL values and lotsa Ia with
a 6CG7 or a pair of EL84, EL86 etc, are good. Consider the operation
of any LTP with a 6SN7/6CG7 low µ triode pair and equal + and -
30Vrms outputs, and gain of each triode = 15. With one grounded grid,
you need -2Vrms input to the live grid you get -1V at the common
cathodes. So the Va across the input tube is 31Vrms and Va across the
grounded grid tube it is 29Vrms, and so there is slight imbalance of
Ea and therefore of the 2H and the stage will produce 2H even if both
triodes are really identical. But balance is fair, and the 2H is
usually negligible. Maybe it cancels with 2H from the SET input stage,
or with some slight 2H in the OP stage, and maybe it don't, but PP
amps all seem to produce *some* 2H.
But the main THD from an LTP is the 3H, which adds to that produced in
the OP stage unless the OP stage 3H has oppositely phased 3H which
rarely ever occurs, so one should be keen to reduce 3H anywhere it is
produced, while also minimizing 2H anywhere.
To get the best Va balance across each triode in an LTP the pair
should have balanced drive to each grid, as it was done with
Williamson's balance drive amp. Now Williamson used SET input + SET
concertina, but he could have used the same 2 triodes as an LTP input
stage which would have largle eliminated any 2H from teh SET input
stage. Alas he didn't have a decent transistor to bung in as the tail
for the input stage CCS. But where the input LTP only has to produce
about a volt from each anode to drive the following balanced amp it
doesn't matter about the Va imbalance and 2H because this 2H will bea
microscopic amount. If the balanced amp as Willy made it has its
common cathode R increased to about 4k7, then the stage self balances
far better and gives less THD. In recent years I have used the LTP
with CCS forthe first stage with input to one grid and GNFB to the
other grid and then had a pair of EL84 in triode in a balanced amp
with a common Rk of at least 4k7 to -100V, and the dynamics and
clarity of music became astounding. Each EL84 in triode with Ia = 10mA
does about the same job with same gain as 4 triode sections of
6SN7/6CG7, or is like 4 x 6J5 in parallel. But the Ra of the EL84 is
only 2k2 at ia = 10mA so any Miller C in the OP stage is handled
better. In Ming-Da I have here with PP 845, there are a pair of 300B
in LTP for the driver amp. It sounds fantabulous. Old dead bean
counters are spinning in their graves at what Chinese sometimes do to
make their amps spectacular looking. Unfortunately, the Chinese often
turn music time into a spectacular event with thunder and flames, and
the repairman has to find where the Cracker was hidden, ready to go
off when conditions would soon allow. But once you remove Crackers
from Ming Da, wow, PP 845 are really something. How can I just
consider British and American trends of the past without thought of
the present, and the the Chinese? Not easily.

Patrick Turner.

[Patrick Turner]

>
> >And so often one will say to a CEO, "Jesus Fred, doncha reckon if the
> >OPT was smaller and lighter you'd make more profit?" *CEO replies,
> >"Yeah, your'e right again Bill, let's talk to the winder guy...", and
> >its a little more quality demolished by a bean counter.
>
> Nothing but your wholly fabricated B.S. fantasies.

OK, cross to being a fly on the wall in BP boardroom, about 4 years
ago.

CEO, "Fred, you got those costings of gulf drilling?"
Accountant, "Yes Bill, costs are extremely high and to get a return at
current gas price we need to lower costs."
CEO, "Oh, how do we do that? any suggestions?"
Acc, "Well if we leave out the popenfusler pipe frame and use a
vargated cement system instead of the usual fiodikic kantel method, we
save 6 billion dollars over 4 years thus increasing profits by 2
billion..."
CEO, "Ah, of course. Well let's do that vargate method then.."

And that's how acountants get to design the drilling process in the
gulf near you, with seriously high risks taken.

Patrick Turner.

[Patrick Turner]

On Jun 1, 3:06*pm, Bret Ludwig > wrote:
> *So prejudice remains, but is
>
> > still breaking down and the arabs will blend in a generation and Islam
> > fades to relative unimportance and the whole becomes homogenous and
> > Whites slowly appreciate what the arabs bring. It was the arabs who
> > brought coffee to the west in the first place. And before that we sent
> > the crusades to butcher them. Its amazing so few Islamic extremists
> > like Arsole Bin Laden have come to spoil the party we've been having
> > at the expense of brown skin exploitation by Whites. We have a White
> > Woman as our dear leader and she's having dreadful trouble dealing
> > with horrible untidy unwashed brown illegals, and she plans to do all
> > sorts of inhumane things to them. She's also having frightful trouble
> > getting ppl to believe in her Carbon Tax. Now just where is a good
> > strong fit brown man who can be a good leader when you want one?
>
> *5000 years of history calls bull**** on this. You'd be smart to boot
> all nonwhites except for the abbos and put them in a nice, safe fenced
> off area where they can live as they always have with NO CONTACT with
> the whites. Leave them alone as if whites never came so people can see
> what 50,000 years of progress is for a 55 IQ race. *And shoot any
> white who ****s one. Race mixing equals death for any people.

The world won't mind when you die. Most would think some time soon
would be fine.
And you'll never be missed by very many.

Patrick Turner.

[Bret Ludwig[_2_]]

>
> I owned a Marantz 8B in the day, I would have thought it would have received
> high marks from Patrick, at least as high he would give any commercial product. *
> It even uses the sort of circuit he espouses, I'm not sure if the OPT would be
> up to his standards though.
>
> I never heard of the Marantz 9 or 9C?
>
>

God catch. The 7 and 7C were the preamps, they are suspiciously
identical to the Mc C22, but better built and several years earlier.
The 7T is the solid state version and not a bad pre itself.

The 9 (no 9B or 9C) was a power amp and does not sound all that
great, but looks impressive. The 10 and 10B were the tuners, with a
scope, which impresses the unwashed. The later Day Sequerra has a spec
an, shich is more useful, but not as well desgned as what's in most
communications service monitors.

[Bret Ludwig[_2_]]

>
> The Marantz OPT takes most of its LF NFB from the 4 ohm tap on the
> sec. But there is an additional NFB winding with its live end connectd
> to the 16 ohm tap via 10 ohms, and the NFB winding feeds HF NFB to the
> V1 cathode via 1.2nF. I'd guess the NFB winding does not experience
> the same phase shift caused by LL and the load at HF, so Marantz
> manages to apply NFB over a wide BW without trying to fix the phase
> lag at HF. But without having a Marantz here to examine, I cannot say
> exactly how well the arrangement works, or understand exactly how
> Marantz wound its OPTs. How can I endorse something I have never
> examined properly? Impossible. But if Marantz had used a 5P x 4S
> interleaving pattern with 6 secondary sections each for 16, 8 &4 ohms
> and all paralleled, there would have been no need for a NFB winding
> because such interleaving with paralleled secs give wide BW for this
> sort of amplifier as Williamson and McIntosh have so so clearly
> established over the last 60 years. Tapped secondaries usually have
> higher winding resistance than *where 4 sec sections are strapped in
> different patterns for the load match variations.

That's called "British Secondaries". Americans went with the 16/8/4
arrangement because that was more convenient for the USER. The
Mercury Magnetics VTO100 in the old VTLs uses this as well. I think a
lot of Partridges and the Radford used this as well. My guess is the
VTO100 is a Radford copy.


Most manufactuers
> have used appallingly thin wire in OPT secs and rarely ever have 4 Sec
> sections; two if you are lucky, and often the two will each be a match
> for 4 ohms, so that the two series S sections give 16 ohms, a tap
> along one section gives 8 ohms, and only one section is then used for
> the 4 ohm match and it is with 4 ohms that there is the highest LL and
> worst BW and highest instability and highest winding losses. As i
> said, for good performance for a 50W OPT, you'll need 5P x 4S, and
> each Sec section should be a match for 16 and so with 4 ohms you still
> have 5P x 4S interleaving, even though 1/2 the sec turns are unused.
> The strapped method of changing Z match on OPTs is often done poorly.
> For example, in Quad-II there are only two link changes needed for 8
> or 16 ohms, but no official match for 4 ohms. Walker must have
> pondered how to set up the OPT and its strapping method long and hard
> to satisfy a Nation Full of Dumbos who are confused if forced to count
> beyond 3. Quad-II would be a MUCH better amp if it were possible to
> strap *all OPT secs to get a wasteless arrangement of secs so that
> every length of secondary wire had the same current density.
> Then the Quad-II would have allowed a P-S load match of 4k0 : 4 ohms
> which would better suit most modern LS, and of course using 8 ohms on
> the 4 ohm outlet gives 8k0 : 8 ohms and nearly all class A which suits
> the old junk circuit best. See why I say old junk is OLD JUNK?
> Its because I can see that the old gizas who designed all that old
> junk *could* have made masterpeices with an extra 2 hour's thought and
> 4 hour's more labour. *But alas, the designers were addicted to
> mediocrity.
>
Well Patrick, you are just so much smarter than those old
guys.......No one did that then because it was not necessary.

You are a crank, is the bottom line.

[Patrick Turner]

On Jun 4, 3:07*pm, Bret Ludwig > wrote:
> > The Marantz OPT takes most of its LF NFB from the 4 ohm tap on the
> > sec. But there is an additional NFB winding with its live end connectd
> > to the 16 ohm tap via 10 ohms, and the NFB winding feeds HF NFB to the
> > V1 cathode via 1.2nF. I'd guess the NFB winding does not experience
> > the same phase shift caused by LL and the load at HF, so Marantz
> > manages to apply NFB over a wide BW without trying to fix the phase
> > lag at HF. But without having a Marantz here to examine, I cannot say
> > exactly how well the arrangement works, or understand exactly how
> > Marantz wound its OPTs. How can I endorse something I have never
> > examined properly? Impossible. But if Marantz had used a 5P x 4S
> > interleaving pattern with 6 secondary sections each for 16, 8 &4 ohms
> > and all paralleled, there would have been no need for a NFB winding
> > because such interleaving with paralleled secs give wide BW for this
> > sort of amplifier as Williamson and McIntosh have so so clearly
> > established over the last 60 years. Tapped secondaries usually have
> > higher winding resistance than *where 4 sec sections are strapped in
> > different patterns for the load match variations.
>
> *That's called "British Secondaries". Americans went with the 16/8/4
> arrangement because that was more convenient for the USER. *The
> Mercury Magnetics VTO100 in the old VTLs uses this as well. I think a
> lot of Partridges and the Radford used this as well. My guess is the
> VTO100 is a Radford copy.
>
> *Most manufactuers
>
>
>
> > have used appallingly thin wire in OPT secs and rarely ever have 4 Sec
> > sections; two if you are lucky, and often the two will each be a match
> > for 4 ohms, so that the two series S sections give 16 ohms, a tap
> > along one section gives 8 ohms, and only one section is then used for
> > the 4 ohm match and it is with 4 ohms that there is the highest LL and
> > worst BW and highest instability and highest winding losses. As i
> > said, for good performance for a 50W OPT, you'll need 5P x 4S, and
> > each Sec section should be a match for 16 and so with 4 ohms you still
> > have 5P x 4S interleaving, even though 1/2 the sec turns are unused.
> > The strapped method of changing Z match on OPTs is often done poorly.
> > For example, in Quad-II there are only two link changes needed for 8
> > or 16 ohms, but no official match for 4 ohms. Walker must have
> > pondered how to set up the OPT and its strapping method long and hard
> > to satisfy a Nation Full of Dumbos who are confused if forced to count
> > beyond 3. Quad-II would be a MUCH better amp if it were possible to
> > strap *all OPT secs to get a wasteless arrangement of secs so that
> > every length of secondary wire had the same current density.
> > Then the Quad-II would have allowed a P-S load match of 4k0 : 4 ohms
> > which would better suit most modern LS, and of course using 8 ohms on
> > the 4 ohm outlet gives 8k0 : 8 ohms and nearly all class A which suits
> > the old junk circuit best. See why I say old junk is OLD JUNK?
> > Its because I can see that the old gizas who designed all that old
> > junk *could* have made masterpeices with an extra 2 hour's thought and
> > 4 hour's more labour. *But alas, the designers were addicted to
> > mediocrity.
>
> *Well Patrick, you are just so much smarter than those old
> guys.......No one did that then because it was not necessary.

There were very few 4 ohm speakers in 1950.
>
> *You are a crank, is the bottom line.

Indeed, and I can say why.

Patrick Turner.