[Multi-grid]

On Nov 3, 9:30 pm, robert casey wrote:
If you mean can you use one half of a PP output transformer for SE,
the answer is most definitely no. An SE transfomer is distinguished
from a PP one by an air gap.
There is a way to use a transformer without an airgap for SE; it is
called parafeed, to indicate that the B+ is shunted in parallel to the
transformer primary, so that the output doesn't carry the current and
can therefore be designed to a more relaxed specificaiton. You also
need a big blocking cap, which some say is out of the signal and some
say can be heard; you make your choice and take your chances.

One could use a push-pull output transformer om a single-ended design,
if you also send a steady DC current (equal to the quiescent class A
current of the tube) thru the other half of the primary from the
centertap (connected to B+) to the unused side, via most likely a power
resistor to ground. But that's rather wasteful of the power you went to
the effort to build a power supply to supply that and the tube's side.
So nobody ever does that, except maybe only if someone has on hand some
P-P output transformers but insists on single endedness. But it would
be a kludge... :-)

Or regap that transformer, but you could ruin the sound quality that was
designed into it (I'm not familiar with transformer design, but I've
since learned not to waste time fooling with power transformers in audio
output work :-) ). You could use the old centertap as a kind of UL
tap, but the tap position is not optimal for UL work. But you'd be best
off saving the P-P transformers for another project, and get single
ended transformers that were designed for that service instead.

hey-Hey!!!,
What you describe is one of the methods to do DC current cancelling.
The other half of the PP primary is straightforward to implement, it
takes the same current as the tube idling opposite it.

One can also use heater current. Best SE amp I ever heard was a 50W
monster that had a piddling little output TX. Through a special
winding went the required 25A of heater current for that valve...no
intentional gap needed anymore.
cheers,
Douglas

[John Byrns]

In article .com,
Multi-grid wrote:

On Nov 3, 9:30 pm, robert casey wrote:

One could use a push-pull output transformer om a single-ended design,
if you also send a steady DC current (equal to the quiescent class A
current of the tube) thru the other half of the primary from the
centertap (connected to B+) to the unused side, via most likely a power
resistor to ground. But that's rather wasteful of the power you went to
the effort to build a power supply to supply that and the tube's side.
So nobody ever does that, except maybe only if someone has on hand some
P-P output transformers but insists on single endedness. But it would
be a kludge... :-)

hey-Hey!!!,
What you describe is one of the methods to do DC current cancelling.
The other half of the PP primary is straightforward to implement, it
takes the same current as the tube idling opposite it.

One can also use heater current. Best SE amp I ever heard was a 50W
monster that had a piddling little output TX. Through a special
winding went the required 25A of heater current for that valve...no
intentional gap needed anymore.


hey-Hey!!!,

Multi-grid, can you give us a few more details on the design of this
amplifier?

I assume it used some sort of DHT transmitting tube, hence the need for
a DC heater supply? To keep from dumping a substantial portion of the
audio power generated by the tube into the tube's heater, I assume there
was also a suitable inductor connected in series with the heater circuit
and the "special winding" on the OPT, to provide a high non lossy
impedance to the audio frequency currents?

Given the need for this special inductor one wonders why the builder of
this amplifier didn't simply go with the conventional parafeed scheme,
whose inductor would presumably use a core of a similar size to that
required with this DC cancelation scheme. The parafeed arrangement
seems like a better more straight forward approach, and as a bonus
provides additional attenuation of any ripple on the B+ power supply. I
assume the reason for this design was that the builder wanted to build
something unusual and unlike anything else seen before?


Regards,

John Byrns

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

[Andre Jute]

Jute:
If you mean can you use one half of a PP output transformer for SE,
the answer is most definitely no. An SE transfomer is distinguished
from a PP one by an air gap.
There is a way to use a transformer without an airgap for SE; it is
called parafeed, to indicate that the B+ is shunted in parallel to the
transformer primary, so that the output doesn't carry the current and
can therefore be designed to a more relaxed specificaiton. You also
need a big blocking cap, which some say is out of the signal and some
say can be heard; you make your choice and take your chances.

Casey:
One could use a push-pull output transformer om a single-ended design,
if you also send a steady DC current (equal to the quiescent class A
current of the tube) thru the other half of the primary from the
centertap (connected to B+) to the unused side, via most likely a power
resistor to ground. But that's rather wasteful of the power you went to
the effort to build a power supply to supply that and the tube's side.
So nobody ever does that, except maybe only if someone has on hand some
P-P output transformers but insists on single endedness. But it would
be a kludge... :-)

Or regap that transformer, but you could ruin the sound quality that was
designed into it (I'm not familiar with transformer design, but I've
since learned not to waste time fooling with power transformers in audio
output work :-) ). You could use the old centertap as a kind of UL
tap, but the tap position is not optimal for UL work. But you'd be best
off saving the P-P transformers for another project, and get single
ended transformers that were designed for that service instead.

Multi-grid:
hey-Hey!!!,
What you describe is one of the methods to do DC current cancelling.
The other half of the PP primary is straightforward to implement, it
takes the same current as the tube idling opposite it.

Okay, but wasteful.

One can also use heater current. Best SE amp I ever heard was a 50W
monster that had a piddling little output TX. Through a special
winding went the required 25A of heater current for that valve...no
intentional gap needed anymore.
cheers,
Douglas

It isn't clear to me at all how "once can use the heater current",
presumably for some purpose beyond heating the filaments. Can you
please explain more, or provide a reference, or even an outline sketch
of connections.

Andre Jute
Visit Jute on Amps at http://members.lycos.co.uk/fiultra/
"wonderfully well written and reasoned information
for the tube audio constructor"
John Broskie TubeCAD & GlassWare
"an unbelievably comprehensive web site
containing vital gems of wisdom"
Stuart Perry Hi-Fi News & Record Review

[Patrick Turner]

John Byrns wrote:

In article CfGWi.1359$8S5.242@edtnps82, "Dave"
wrote:

"Andre Jute" wrote in message
ups.com...

And NFB up the kazoo. 0.1 per cent is a figure commonly bandied about
but I'm not overly impressed. I know for a fact that people cannot
hear as much as 3/4 per cent second harmonic but can hear that much
odd harmonic very clearly, and many people can hear or are made
uncomfortable by 0.3 per cent odd harmonics. What you want to do is
not to measure at full power but at some lower power where you will
actually use the amp; 1W or 2.83V into 8ohm is a common level with
even semi-sensitive speakers.


So... is ALL negative feedback bad? I am 40 with some background in
electrical engineering and learned nothing but transistor theory at
school... thermal runaway pretty much mandates feedback in all transistor
amps.

There are typically two different feedback mechanisms at work in a
transistor amplifier. The first, which is the one you are referring to
stabilizes the DC bias, or operating point, of the transistors to
prevent thermal runaway as you describe, and also to insure that the
"crossover" region of the transfer characteristic has the desired degree
of overlap. The second is the overall loop NFB, which is what Andre is
talking about, and is used to reduce the audio frequency distortion and
noise produced in the amplifier, as well as to stabilize the gain of the
amplifier, as the gain of discrete transistors is notoriously
inconsistent from sample to sample.

You left out one other very important common NFB loop.

This is the connection of the output transistors as emitter followers,
reducing the gain of the output stage to nearly 1.0.

This is often an amount of local series voltage NFB = about 40dB.

The global series voltage NFB is applied after the EF connection and
back to input
which subjects the driver amp and output stage already with its 40dB of
local NFB
to perhaps 60dB of NFB over all.

A lot of what I read about 'audiophile' grade amps is pro-znfb. Why?

It's because of a lack of understanding in the audiophile community.
NFB can work wonders when correctly applied by someone who knows what
they are doing, but it can also do serious harm when incompetently
applied. Bad experiences with amplifiers using NFB of the latter type
lead to the typical audiophile' negative feelings towards NFB.

Indeed...

Patrick Turner.

Regards,

John Byrns

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

[Patrick Turner]

Andre Jute wrote:

On Nov 2, 4:28 pm, Patrick Turner wrote:
Andre Jute wrote:

On Oct 31, 2:41 pm, "Dave" wrote:
Is there any quick "in a nutshell" explanation why there aren't more pentode
amp designs? I'm guessing it has to do with extreme non-linearity. I am
building a 10W EL84-based ultralinear amp. The triode conversion is a snap
but it drops me down to 5W which is not enough oomph for my 88dB speakers.
Pentode mode would give me 15W which I am inclined to try if it's not too
difficult.

Can anybody point me to a resource where I could figure out the proper
screen voltage required for pentode mode EL84's with an 8K output tranny and
a B+ of 300V? does this voltage have to be regulated, or could I just drop
the B+ with a resistor?

Thx

Dave

I wasn't aware of a shortage of pentode amps. But a pentode amp has
more gain than those with ultralinear connection, and thus can have
more global feedback applied, and thus lower THD.

However, I put a pentode/ultralinear/triode switch and a variable/off
negative feedback switch in the best amp I ever designed, my T113
"Triple Threat", Class A1 PP EL34 of pretty straightforward,
conservative design. Then I tested it with chamber musicians
listerning to their own recordings. They universally hated the pentode
sound, and loved the triode sound, on which the amp is usually played
with zero NFB.

The explanation is simple. Loop NFB causes artifacts of ever lower
magnitude but higher order. These high order distortions, even at 60dB
below conscious perception are very, very disturbing, whereas second
harmonic up to three-quarter per cent cannot even be distinguished by
professional musicians. It is a subliminal effect, and of course in
pentode mode it is exaggerated. People look at the total harmonic
distortion but in fact the higher harmonics must be weighted much more
heavily than the second harmonic to account for its extraordinary
subliminal effect, often described as "edgineess" by professional
musicians.

-60dB, at average listeining levels????

Say a volt is average, then -60dB artifcats = 1mV.

1mV of grunge isn't exactly loud in most speakers......

Try Quad ESL, though of course not at 1W.

ESL are generally so insensitive that residual amp noise
isn't heard above recorded venue noise and 1mV of grunge isn't heard.

Or try horns at 1W.

1mV of ****e matters not with horns as well because the same SNR would
apply.

The volume control isn't selective about letting the grunge through
when attenuating the music.

So with horns, one just uses less vome than with the ESL.

A volt into horns is deafening.

But Becase horns require maybe 1/10 of the voltage of ESL or "normal"
modern speakers, the amp can be SET and not be producing many IMD
products.
THD & IMD reduces with reduced power levels.


You'd be
amazed what you can hear.

Sometimes I am indeed amazed at what I hear..

About half of professional musicians can are
still disturbed by the artifacts at 60dB below; that's more than
enough for me to believe in subliminal perception of IM artifacts.

Not all musicians are sensitive to 60dB artifacts.

In fact huge differeneces in hearing abilities range across the
population generally,
including musician types. Do we include Sid Vicious, of punk rock fame?
Mick Jagger perhaps?
Is Nigel Kennedy likely to hear -60 dB artifcats any better than anyone
else?
Does Nigel use a special triode amp?

Most "musos" in the rock'n'roll field don't like unaltered music.
THeu only really like artifacts when up at about the 15%+ level and have
reverb added, and where
recordingsd are made they usually really hate the sound of their own
voise,
and want the recording studio to process it all so heavily to make it at
all saleable,
and maybe even likable.

The typical distortions created by processing is up to the 20% order of
magnitude,
and its as if they surely prefer and are aware of a bonfire of good
artifacts in front of them
but really don't give a ****e about the candle power of the -60dB
artifact.

Many of the musos I have known do like tube gear because of the gooey
sloppy artifacts produced at gross overload, with some reverb as well...


anyone can hear them when they're only 30dB below perception. I'll
remind you that half a century ago -30dB was considered near enough
perfection... Arny Krueger says in another post that it is easy to set
up a test of whether people can hear 1mV IM; actually I found it very
frustrating getting qualified listeners, which is why in the end I
concentrated on testing professional musicians.

Musicians do not necessarily have any special hearing abilities.

What most good musos do have is a superior ability for tuneful playing
in key
and a sense of rythm. Some will understand the words of opera sung in
english
where I will still need subtitles, and couldn't hum along in tune to
save my life.
They are often dyslectic, a bonus for creativity.
They tend to live crazier lives like many artists.
Their hearing is different to most other ppl, but not superior when it
comes to detection
of low level sound, and indeed despite their giftedness, but by 40 the
tinnitus has set in as badly
as it does with many panel beaters or carpenters.

If an audience of members of the general population are chosen,
Its a good enough choice.
and music played using a volt of average levels, its not hard to
arrange the NFB around an amp to alter the THD from 1%, -40dB to 0.1%
-60dB,
or to 0.01%, -80dB.

A friend has a VAC amp with 4 x 300B and one can adjust the global NFB
from
zero to 9dB applied, and I hear not the slightest difference.
Artifacts would perhaps be above
the -60dB level with or without NFB....
The VAC PP amp does sound very healthy and clean, and right...


You listen to your speakers, not your amp; I would really advise you,
unless you are married to these insensitive speakers, first to get
good sensitive speakers you can live with forever, then build an amp
to suit them. If you have the space, an inexpensive sensitive speaker
you can build easily is The Impresario on my netsite, url under my
sig. EL84 are particularly sweet in triode but of course pitifully
underpowered for insensitive speakers.

I have good enough speakers to make differences in source material
or amplifiers to be heard.



I quite like UL EL84 good for 12 watts AB. But you do need
sensitive speakers over 92dB/W/M.

Of the common tubes, EL84 and EL34 are the greatest ever made, in my
humble opinion.

They sure are good in triode, I will give you that.





I'd prefer an SE 300B amp though....

Nah, not for a first amp; too expensive for messing around. I think
Dave has already made the choice in the SEntry.


Agreed, nearly everyone is NOT drawn to using one lone 300B instead of a
pair of EL84 in class A.

Cost and specialo tranny requirements put the 300B into an untouchable
class
for many tight arsed DIYers with limited skills.

Little do they know that a truly superb PP amp
can be made using a pair of 300B for class AB PO = about 28 watts.

Patrick Turner.



Patrick Turner.

Andre Jute
Visit Jute on Amps athttp://members.lycos.co.uk/fiultra/
"wonderfully well written and reasoned information
for the tube audio constructor"
John Broskie TubeCAD & GlassWare
"an unbelievably comprehensive web site
containing vital gems of wisdom"
Stuart Perry Hi-Fi News & Record Review

[Patrick Turner]

Arny Krueger wrote:

"John Byrns" wrote in message
...
In article ,
"Arny Krueger" wrote:

"Dave" wrote in message
news:CfGWi.1359$8S5.242@edtnps82...

"Andre Jute" wrote in message
ups.com...

I know for a fact that people cannot
hear as much as 3/4 per cent second harmonic but can hear that much
odd harmonic very clearly, and many people can hear or are made
uncomfortable by 0.3 per cent odd harmonics.

This order of harmonics issue is way overblown. Doesn't matter whether it
is
odd or even order nonlinearity, it all makes IM. IM is generally
aharmonic
and it all sounds bad.

But even order IM is much more obvious and annoying in listening tests,
although I suppose others may find odd order IM more annoying, its
probably partly a matter of personal preference.

I've never seen that. Got a reference?

Here's what my analysis says:

Fundamentals: F1 and F2

Second Order IM: F1±F2, F2-F1

Third Order IM: 2F1±F2, 2F2±F1

Fourth Order IM: 2F1±2F2, 2F2±2F1

Fifth Order IM: 3F1±2F2, 3F2±2F1

Almost all sums and differences are inharmonic and therefore likely to be
objectionable.

Are not the IMD products somewhat different between an amp with nearly
all 2H THD
as opposed to one with mainly 3H THD?

And then there is ordinary real music from instruments.
Presumably a fair amount of IMD is included.

And then the levels have to be considered.
If the THD is low, so is IMD and as the order of IMD products become
higher,
their levels get lower and lower.....


So you need to list the conditions and levels of a REAL amp in a REAL
world listening experience before the above "reference" becomes
meaningful.

Patrick Turner.

[Multi-grid]

On Nov 4, 3:32 am, Andre Jute wrote:
Jute:

Casey:
One could use a push-pull output transformer om a single-ended design,
if you also send a steady DC current (equal to the quiescent class A
current of the tube) thru the other half of the primary from the
centertap (connected to B+) to the unused side, via most likely a power
resistor to ground. But that's rather wasteful of the power you went to


Multi-grid:

hey-Hey!!!,
What you describe is one of the methods to do DC current cancelling.
The other half of the PP primary is straightforward to implement, it
takes the same current as the tube idling opposite it.

Okay, but wasteful.

One can also use heater current. Best SE amp I ever heard was a 50W
monster that had a piddling little output TX. Through a special
winding went the required 25A of heater current for that valve...no
intentional gap needed anymore.
cheers,
Douglas

It isn't clear to me at all how "once can use the heater current",
presumably for some purpose beyond heating the filaments. Can you
please explain more, or provide a reference, or even an outline sketch
of connections.

Andre Jute

- Show quoted text -

Well Andre,
Do you see how the example using a PP output is using half the primary
to cancell DC-generated flux in the core? It takes the same amount of
current as is being passed at idle by the tube we're applying signal
to.
Cheers,
Douglas

[Andre Jute]

On Nov 4, 6:52 am, Patrick Turner wrote:

Musicians do not necessarily have any special hearing abilities.

Yes, they do: they have trained perception. They listen consciously.
Non-audiophiles from the general population cannot even hear the
difference between a boombox played through good speakers and a Class
A PP tube amp played through the same speakers. To them it is all
"nice", useless for tests.

If I could find enough experienced audiophiles -- defined as having
trained their own aural perception -- available on a regular basis, I
would use them instead. it was just easier in my particular
circumstances to find as many classical musicians as required.

It should also be observed that most audiophiles talk big about their
golden ears but in blind tests have poor discrimination, so that you
first require tests to sort out the good listeners. That shocked me;
for a while I wondered if the meterheads weren't right, if vanishing
THD numbers aren't the holy grail after all... But you don't want to
hear about the anguish of an open mind.

For the innocent: The point of listening tests isn't to discover which
amp or topology is "better": I already know from comparison with years
in the concert halls which kinds of amps and which topologies I prefer
(Class A1 triodes or trioded pentodes in PP with ESL, and ditto in SET
with horns). The point of tests is to determine why these topologies
affect the emotions differently; psycho-acoustics is probably the last
frontier in audio-electronics.

Andre Jute
"I was at a board meeting for the LA Chapter of the Audio Engineering
Society last night on XM Satellite radio audio and data transmission.
Sadly, we missed you there, and at the SMPTE and Acoustical Society
recent meetings as well. Everyone was asking, 'Where is that wonderful
Andre Jute? The world just doesn't rotate without him...'" -- John
Mayberry, Emmaco

[Andre Jute]

On Nov 4, 12:02 pm, Multi-grid wrote:
On Nov 4, 3:32 am, Andre Jute wrote:



Jute:

Casey:
One could use a push-pull output transformer om a single-ended design,
if you also send a steady DC current (equal to the quiescent class A
current of the tube) thru the other half of the primary from the
centertap (connected to B+) to the unused side, via most likely a power
resistor to ground. But that's rather wasteful of the power you went to

Multi-grid:

hey-Hey!!!,
What you describe is one of the methods to do DC current cancelling.
The other half of the PP primary is straightforward to implement, it
takes the same current as the tube idling opposite it.

Okay, but wasteful.

One can also use heater current. Best SE amp I ever heard was a 50W
monster that had a piddling little output TX. Through a special
winding went the required 25A of heater current for that valve...no
intentional gap needed anymore.
cheers,
Douglas

It isn't clear to me at all how "once can use the heater current",
presumably for some purpose beyond heating the filaments. Can you
please explain more, or provide a reference, or even an outline sketch
of connections.

Andre Jute

- Show quoted text -

Well Andre,
Do you see how the example using a PP output is using half the primary
to cancell DC-generated flux in the core? It takes the same amount of
current as is being passed at idle by the tube we're applying signal
to.
Cheers,
Douglas

Sure, standard stuff, but that's not my question. That is about
quiescent plate current. I want you to show me how this works:

Through a special
winding went the required 25A of heater current for that valve...no
intentional gap needed anymore.

They're your words and they don't make sense to me. Take all the space
you need. Please feel free to treat me as a total ignoramus and
explain in words of one syllable, with all the tees crossed and all
the eyes dotted so that there can be no misunderstanding. A schematic
is always good to avoid misunderstanding.

Andre Jute
Visit Jute on Amps at http://members.lycos.co.uk/fiultra/
"wonderfully well written and reasoned information
for the tube audio constructor"
John Broskie TubeCAD & GlassWare
"an unbelievably comprehensive web site
containing vital gems of wisdom"
Stuart Perry Hi-Fi News & Record Review

[Patrick Turner]

Dave wrote:

"Andre Jute" wrote in message
ups.com...
Note that you need
single-ended transformers, not push-pull.

Would a push-pull present only half the impedence to the tube? I.e. a pp is
sort of like two transformers in one?

Yes, there are virtually two SE OPTs which are tied together tightly
with magnetic coupling.

One could make a PP amp with two SE amps, with secondaries of the two
transfromers in parallel,
but different phase, and with grid signals of opposite phase....

But its only really good for class A operation.

Patrick Turner.

[Patrick Turner]

Andre Jute wrote:

On Nov 2, 11:17 pm, Eeyore
wrote:
Andre Jute wrote:
"Arny Krueger" wrote:
"Andre Jute" wrote in message

That's true, of course, but I think some, who were educated in silicon
only as Dave was, come to tube amps with a silicon mindset that NFB is
the cure-all, that if a little is good, more must be better, and lots
will be superb.

Spoken like someone who lacks experience with how coursed in feedback is
taught.

Courses in feedback are rarely if ever couched in either terms of either SS
or tubes.

You're wanking, Krueger. By the time Dave was educated, there were no
more tubes. -- AJ

Irrelevant to feedback theory. Feedback works in the same way, whatever active
parts are in use. It is, after all, merely maths at the end of the day.

Graham

You two soundbite mentalities have missed the point altogether. Again.

The principles of negative feedback are just math, sure. But
electronics engineers who are taught to apply negative feedback are
now differently instructed to the time when tubes were dominant. For
instance, Julian L. Bernstein, Associate Dean of the RCA Day Schools,
in his book Audio Systems makes the point that NFB must be used with
restraint. By contrast, modern EEs are taught that mo' neg' is
betta neg' or what whatever the current street-talk-derived
vernacular is on campus this week. You two superannuates are just too
old and disconnected and unhip to discover this for yourselves. I made
exactly two phone calls to find out all of that.

Andre Jute
Mr Street Cred

One of the "ultimate" and "cutting edge" amplifiers is designed
by Halcro of Sth Australia, and boasts 0.0001% thd at 199 watts right up
to 20kHz with class AB mosfets in the amp.

They think more NFB is best.

The HK audio club said of the Halcro gear when it was demonstrated,

" Ah, Halcro, it like 300B, but just go louder...."

Something tells me the HK audio club members probably got all the music
they could ever wish for
from a 300B, and frankly, a Halcro was a waste of time and a terrible
huge expense.

Never did almost nothing cost so much, ie, low THD cost heaps.

How the HK club members mention Halcro and a 300B in the same sentence
with such inscrutability must have raised weary eyebrows in the Halcro
CEO office...

Anyway, one can happily leave two noughts out of Halcros THD figures,
ie, reduce the NFB enormously, and hear utterly no change whatsoever.

But probably that wouldn't make the amps any cheaper.

Patrick Turner.

[Patrick Turner]

robert casey wrote:


If you mean can you use one half of a PP output transformer for SE,
the answer is most definitely no. An SE transfomer is distinguished
from a PP one by an air gap.

There is a way to use a transformer without an airgap for SE; it is
called parafeed, to indicate that the B+ is shunted in parallel to the
transformer primary, so that the output doesn't carry the current and
can therefore be designed to a more relaxed specificaiton. You also
need a big blocking cap, which some say is out of the signal and some
say can be heard; you make your choice and take your chances.


One could use a push-pull output transformer om a single-ended design,
if you also send a steady DC current (equal to the quiescent class A
current of the tube) thru the other half of the primary from the
centertap (connected to B+) to the unused side, via most likely a power
resistor to ground. But that's rather wasteful of the power you went to
the effort to build a power supply to supply that and the tube's side.
So nobody ever does that, except maybe only if someone has on hand some
P-P output transformers but insists on single endedness. But it would
be a kludge... :-)

Or regap that transformer, but you could ruin the sound quality that was
designed into it (I'm not familiar with transformer design, but I've
since learned not to waste time fooling with power transformers in audio
output work :-) ). You could use the old centertap as a kind of UL
tap, but the tap position is not optimal for UL work. But you'd be best
off saving the P-P transformers for another project, and get single
ended transformers that were designed for that service instead.

Trying to convert a PP OPT for SE use with current sources applied to
taps, ends is a pile of BS.
Its doable, but why oh why?

If an ungapped PP OPT is to be used for an SE tube, then it
is best done using a parallel feed system where
you have a choke of high inductance and gapped ideally so the inductance
does not cause a 3 dB loss of gain above 20Hz.

Then one end of the PP OPT primary grounded, and the other taken via
about 40uF to the tube anode.

There is then no dc in the OPT, and no need for a gap.

No insulation problems either.

Trouble could be when NFB is used though because the extra cap coupling
from anode to
OPT with its L shunting RL will give an ultimate 180 degree phase shift
at very low F.

Therefore, the use of NFB from tube anode back to previous stages should
be explored.

Patrick Turner.

[John Byrns]

In article ,
Patrick Turner wrote:

John Byrns wrote:

In article CfGWi.1359$8S5.242@edtnps82, "Dave"
wrote:

"Andre Jute" wrote in message
ups.com...

And NFB up the kazoo. 0.1 per cent is a figure commonly bandied about
but I'm not overly impressed. I know for a fact that people cannot
hear as much as 3/4 per cent second harmonic but can hear that much
odd harmonic very clearly, and many people can hear or are made
uncomfortable by 0.3 per cent odd harmonics. What you want to do is
not to measure at full power but at some lower power where you will
actually use the amp; 1W or 2.83V into 8ohm is a common level with
even semi-sensitive speakers.


So... is ALL negative feedback bad? I am 40 with some background in
electrical engineering and learned nothing but transistor theory at
school... thermal runaway pretty much mandates feedback in all transistor
amps.

There are typically two different feedback mechanisms at work in a
transistor amplifier. The first, which is the one you are referring to
stabilizes the DC bias, or operating point, of the transistors to
prevent thermal runaway as you describe, and also to insure that the
"crossover" region of the transfer characteristic has the desired degree
of overlap. The second is the overall loop NFB, which is what Andre is
talking about, and is used to reduce the audio frequency distortion and
noise produced in the amplifier, as well as to stabilize the gain of the
amplifier, as the gain of discrete transistors is notoriously
inconsistent from sample to sample.

You left out one other very important common NFB loop.

This is the connection of the output transistors as emitter followers,
reducing the gain of the output stage to nearly 1.0.

This is often an amount of local series voltage NFB = about 40dB.

I actually thought of mentioning that in my post, but I decided to drop
it to keep the focus on the subjects of loop NFB and "thermal runaway"
which the earlier poster was talking about. I feel it's better to keep
threads more focused and not branch out too much unnecessarily.


Regards,

John Byrns

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

[John Byrns]

In article . com,
Andre Jute wrote:

On Nov 4, 12:02 pm, Multi-grid wrote:
On Nov 4, 3:32 am, Andre Jute wrote:



Jute:

Casey:
One could use a push-pull output transformer om a single-ended
design,
if you also send a steady DC current (equal to the quiescent class A
current of the tube) thru the other half of the primary from the
centertap (connected to B+) to the unused side, via most likely a
power
resistor to ground. But that's rather wasteful of the power you went
to

Multi-grid:

hey-Hey!!!,
What you describe is one of the methods to do DC current cancelling.
The other half of the PP primary is straightforward to implement, it
takes the same current as the tube idling opposite it.

Okay, but wasteful.

One can also use heater current. Best SE amp I ever heard was a 50W
monster that had a piddling little output TX. Through a special
winding went the required 25A of heater current for that valve...no
intentional gap needed anymore.
cheers,
Douglas

It isn't clear to me at all how "once can use the heater current",
presumably for some purpose beyond heating the filaments. Can you
please explain more, or provide a reference, or even an outline sketch
of connections.

Andre Jute

- Show quoted text -

Well Andre,
Do you see how the example using a PP output is using half the primary
to cancell DC-generated flux in the core? It takes the same amount of
current as is being passed at idle by the tube we're applying signal
to.
Cheers,
Douglas

Sure, standard stuff, but that's not my question. That is about
quiescent plate current. I want you to show me how this works:

Through a special
winding went the required 25A of heater current for that valve...no
intentional gap needed anymore.

They're your words and they don't make sense to me. Take all the space
you need. Please feel free to treat me as a total ignoramus and
explain in words of one syllable, with all the tees crossed and all
the eyes dotted so that there can be no misunderstanding. A schematic
is always good to avoid misunderstanding.

Andre, you are wasting your time with Multi-grid, you won't get any
answers from him as he hasn't yet reached the point in his studies where
he can even understand the question.


Regards,

John Byrns

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

[Andre Jute]

On Nov 4, 3:52 pm, John Byrns wrote:
In article . com,
Andre Jute wrote:



On Nov 4, 12:02 pm, Multi-grid wrote:
On Nov 4, 3:32 am, Andre Jute wrote:

Jute:

Casey:
One could use a push-pull output transformer om a single-ended
design,
if you also send a steady DC current (equal to the quiescent class A
current of the tube) thru the other half of the primary from the
centertap (connected to B+) to the unused side, via most likely a
power
resistor to ground. But that's rather wasteful of the power you went
to

Multi-grid:

hey-Hey!!!,
What you describe is one of the methods to do DC current cancelling.
The other half of the PP primary is straightforward to implement, it
takes the same current as the tube idling opposite it.

Okay, but wasteful.

One can also use heater current. Best SE amp I ever heard was a 50W
monster that had a piddling little output TX. Through a special
winding went the required 25A of heater current for that valve...no
intentional gap needed anymore.
cheers,
Douglas

It isn't clear to me at all how "once can use the heater current",
presumably for some purpose beyond heating the filaments. Can you
please explain more, or provide a reference, or even an outline sketch
of connections.

Andre Jute

- Show quoted text -

Well Andre,
Do you see how the example using a PP output is using half the primary
to cancell DC-generated flux in the core? It takes the same amount of
current as is being passed at idle by the tube we're applying signal
to.
Cheers,
Douglas

Sure, standard stuff, but that's not my question. That is about
quiescent plate current. I want you to show me how this works:

Through a special
winding went the required 25A of heater current for that valve...no
intentional gap needed anymore.

They're your words and they don't make sense to me. Take all the space
you need. Please feel free to treat me as a total ignoramus and
explain in words of one syllable, with all the tees crossed and all
the eyes dotted so that there can be no misunderstanding. A schematic
is always good to avoid misunderstanding.

Andre, you are wasting your time with Multi-grid, you won't get any
answers from him as he hasn't yet reached the point in his studies where
he can even understand the question.

Yes, I suspected that. That is why I call it the "Duggled Method" to
indicate I think Dougles Muti-grid is sucking on a hind tit he hasn't
properly grasped.

Regards,

John Byrns

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

Still, wouldn't it be a fabulous invention to make the filament
current do something else as well?

Andre Jute
"I was at a board meeting for the LA Chapter of the Audio Engineering
Society last night on XM Satellite radio audio and data transmission.
Sadly, we missed you there, and at the SMPTE and Acoustical Society
recent meetings as well. Everyone was asking, 'Where is that wonderful
Andre Jute? The world just doesn't rotate without him...'" -- John
Mayberry, Emmaco

[Eeyore]

Andre Jute wrote:

Patrick Turner wrote:

Musicians do not necessarily have any special hearing abilities.

Yes, they do: they have trained perception. They listen consciously.
Non-audiophiles from the general population cannot even hear the
difference between a boombox played through good speakers and a Class
A PP tube amp played through the same speakers. To them it is all
"nice", useless for tests.

The same holds true for plenty of musicians too. The idea that ALL musicians
have wonderfully critical hearing is just plain wrong. And those that do have
good critical hearing may not be listening for the audible cues a technical
person will be.

Graham

[Andre Jute]

On Nov 4, 2:52 pm, Patrick Turner wrote:
Dave wrote:

"Andre Jute" wrote in message
oups.com...
Note that you need
single-ended transformers, not push-pull.

Would a push-pull present only half the impedence to the tube? I.e. a pp is
sort of like two transformers in one?

Yes, there are virtually two SE OPTs which are tied together tightly
with magnetic coupling.

One could make a PP amp with two SE amps, with secondaries of the two
transfromers in parallel,
but different phase, and with grid signals of opposite phase....

But its only really good for class A operation.

Patrick Turner.

Careful, Patrick. I think Dave's question is practical, of the "can I
do this" kind, rather than theoretical. Your answer to Robert Casey's
suggestion is more to the point. -- Andre Jute

[Andre Jute]

On Nov 4, 3:03 pm, Patrick Turner wrote:
Andre Jute wrote:

On Nov 2, 11:17 pm, Eeyore
wrote:
Andre Jute wrote:
"Arny Krueger" wrote:
"Andre Jute" wrote in message

That's true, of course, but I think some, who were educated in silicon
only as Dave was, come to tube amps with a silicon mindset that NFB is
the cure-all, that if a little is good, more must be better, and lots
will be superb.

Spoken like someone who lacks experience with how coursed in feedback is
taught.

Courses in feedback are rarely if ever couched in either terms of either SS
or tubes.

You're wanking, Krueger. By the time Dave was educated, there were no
more tubes. -- AJ

Irrelevant to feedback theory. Feedback works in the same way, whatever active
parts are in use. It is, after all, merely maths at the end of the day.

Graham

You two soundbite mentalities have missed the point altogether. Again.

The principles of negative feedback are just math, sure. But
electronics engineers who are taught to apply negative feedback are
now differently instructed to the time when tubes were dominant. For
instance, Julian L. Bernstein, Associate Dean of the RCA Day Schools,
in his book Audio Systems makes the point that NFB must be used with
restraint. By contrast, modern EEs are taught that mo' neg' is
betta neg' or what whatever the current street-talk-derived
vernacular is on campus this week. You two superannuates are just too
old and disconnected and unhip to discover this for yourselves. I made
exactly two phone calls to find out all of that.

Andre Jute
Mr Street Cred

One of the "ultimate" and "cutting edge" amplifiers is designed
by Halcro of Sth Australia, and boasts 0.0001% thd at 199 watts right up
to 20kHz with class AB mosfets in the amp.

They think more NFB is best.

The HK audio club said of the Halcro gear when it was demonstrated,

" Ah, Halcro, it like 300B, but just go louder...."

Something tells me the HK audio club members probably got all the music
they could ever wish for
from a 300B, and frankly, a Halcro was a waste of time and a terrible
huge expense.

They didn't want to say anything negative because the PR dolly from
Halcro was so nice...

Never did almost nothing cost so much, ie, low THD cost heaps.

How the HK club members mention Halcro and a 300B in the same sentence
with such inscrutability must have raised weary eyebrows in the Halcro
CEO office...

Anyway, one can happily leave two noughts out of Halcros THD figures,
ie, reduce the NFB enormously, and hear utterly no change whatsoever.

But probably that wouldn't make the amps any cheaper.

Patrick Turner.

I was going to reply to your claim that you can't hear any difference
between ZNFB and 9dB but can't now find the message in which you said
it in the ferment of messages on RAT -- who said RAT is dying? what a
fool! This is as good a place as any. I'm not surprised at all by your
number. Less than ten years ago Bill May, my late technical guy,
conducted careful blind tests and determined that I could tell GNFB as
low as 6dB. When I did the tests on him, and he had good ears but was
pushing 70, he couldn't hear GNFB until 12dB. This was on a standard
design of trioded PP Class A amp (input, splitter, driver, power
stages). On simpler amps the GNFB could be heard a dB or two lower,
but very design dependent even when within the level of statistical
confidence. A hard and fast rule to answer Dave's earlier question --
how much distortion is permissable? -- is so difficult to answer, once
you are below the crude direct perception level, precisely because the
*aural* effects of the NFB required to lower the harmonics are not
linearly predictable.

Andre Jute
Visit Jute on Amps at http://members.lycos.co.uk/fiultra/
"wonderfully well written and reasoned information
for the tube audio constructor"
John Broskie TubeCAD & GlassWare
"an unbelievably comprehensive web site
containing vital gems of wisdom"
Stuart Perry Hi-Fi News & Record Review

[Patrick Turner]

Andre Jute wrote:

On Nov 4, 6:52 am, Patrick Turner wrote:

Musicians do not necessarily have any special hearing abilities.

Yes, they do: they have trained perception. They listen consciously.
Non-audiophiles from the general population cannot even hear the
difference between a boombox played through good speakers and a Class
A PP tube amp played through the same speakers. To them it is all
"nice", useless for tests.

Jeezzuuus! More than half the musos I know are dumb****s.

A few might have benefitted from being trained musically,
but the majority are not.

The majority are self taught rock/jaz musos, and only a real minority
score well in music reproduction examination tests.



If I could find enough experienced audiophiles -- defined as having
trained their own aural perception -- available on a regular basis, I
would use them instead. it was just easier in my particular
circumstances to find as many classical musicians as required.

The serious audio clubs in Australia such as the Melbourne Audio Club,
MAC,
and Audiophile Society of NSW, ASON contain enough practised and
experienced ppl whose
opinion can be considered seriously when testing AB set ups in front of
them.
I was a member of ASON for some years and demoed my gear several times
and AB'd it in "sound offs" to see what sounded better.

The results embarrassed the guy who believed in triodes with no GNFB.


It should also be observed that most audiophiles talk big about their
golden ears but in blind tests have poor discrimination, so that you
first require tests to sort out the good listeners.

Yes, but there were enough good ears in the club to get as good an idea
about the audio quality as you'd ever want.


That shocked me;
for a while I wondered if the meterheads weren't right, if vanishing
THD numbers aren't the holy grail after all... But you don't want to
hear about the anguish of an open mind.

ASON club members did not hear anything special with gear that had
10 times or lower measured THD/IMD than the tube gear I demoed.

About 1/2 used SS, 1/2 used tube gear. Speakers varied from horns,
generally HQ dynamics, and some ESL.

Sources of the club were also better than average.


For the innocent: The point of listening tests isn't to discover which
amp or topology is "better": I already know from comparison with years
in the concert halls which kinds of amps and which topologies I prefer
(Class A1 triodes or trioded pentodes in PP with ESL, and ditto in SET
with horns). The point of tests is to determine why these topologies
affect the emotions differently; psycho-acoustics is probably the last
frontier in audio-electronics.


Better usually means sounds better to audiophiles, many of whom couldn't
care a hoot about the measurements.
Better to an engineer means it measures better, and engineers
often are dull emotionally, and incapable of listening to music at all.

A 100 times betterment in measurements usually does NOT give a 100 time
betterment in sound quality.

Patrick Turner.




Andre Jute
"I was at a board meeting for the LA Chapter of the Audio Engineering
Society last night on XM Satellite radio audio and data transmission.
Sadly, we missed you there, and at the SMPTE and Acoustical Society
recent meetings as well. Everyone was asking, 'Where is that wonderful
Andre Jute? The world just doesn't rotate without him...'" -- John
Mayberry, Emmaco

[Andre Jute]

Jute:
If you mean can you use one half of a PP output transformer for SE,
the answer is most definitely no. An SE transfomer is distinguished
from a PP one by an air gap.

There is a way to use a transformer without an airgap for SE; it is
called parafeed, to indicate that the B+ is shunted in parallel to the
transformer primary, so that the output doesn't carry the current and
can therefore be designed to a more relaxed specificaiton. You also
need a big blocking cap, which some say is out of the signal and some
say can be heard; you make your choice and take your chances.

Casey:
One could use a push-pull output transformer om a single-ended design,
if you also send a steady DC current (equal to the quiescent class A
current of the tube) thru the other half of the primary from the
centertap (connected to B+) to the unused side, via most likely a power
resistor to ground. But that's rather wasteful of the power you went to
the effort to build a power supply to supply that and the tube's side.
So nobody ever does that, except maybe only if someone has on hand some
P-P output transformers but insists on single endedness. But it would
be a kludge... :-)

Or regap that transformer, but you could ruin the sound quality that was
designed into it (I'm not familiar with transformer design, but I've
since learned not to waste time fooling with power transformers in audio
output work :-) ). You could use the old centertap as a kind of UL
tap, but the tap position is not optimal for UL work. But you'd be best
off saving the P-P transformers for another project, and get single
ended transformers that were designed for that service instead.

Turner:
Trying to convert a PP OPT for SE use with current sources applied to
taps, ends is a pile of BS.
Its doable, but why oh why?

If an ungapped PP OPT is to be used for an SE tube, then it
is best done using a parallel feed system where
you have a choke of high inductance and gapped ideally so the inductance
does not cause a 3 dB loss of gain above 20Hz.

Then one end of the PP OPT primary grounded, and the other taken via
about 40uF to the tube anode.

There is then no dc in the OPT, and no need for a gap.

No insulation problems either.

Trouble could be when NFB is used though because the extra cap coupling
from anode to
OPT with its L shunting RL will give an ultimate 180 degree phase shift
at very low F.

Therefore, the use of NFB from tube anode back to previous stages should
be explored.

Patrick Turner.

It has always seemed to me a parafeed amplifier is a kludge to gimmick
a heathrobinson created by false reasoning. To save the cost of an SE
transformer and permit the use of a PP transformer in SE, the
parafeeder then has to buy a choke and a cap and a larger chassis...

Andre Jute
Last of the big spenders

[Andre Jute]

On Nov 4, 4:41 pm, Eeyore
wrote:
Andre Jute wrote:
Patrick Turner wrote:

Musicians do not necessarily have any special hearing abilities.

Yes, they do: they have trained perception. They listen consciously.
Non-audiophiles from the general population cannot even hear the
difference between a boombox played through good speakers and a Class
A PP tube amp played through the same speakers. To them it is all
"nice", useless for tests.

The same holds true for plenty of musicians too. The idea that ALL musicians
have wonderfully critical hearing is just plain wrong.

What is your problem, Poopie? Where did I say I was talking about "ALL
musicians". Why don't you learn to read? I specifically said, in the
section of my post you stupidly snipped: "it was just easier in my
particular circumstances to find as many classical musicians as
required."

And those that do have
good critical hearing may not be listening for the audible cues a technical
person will be.

You're a moron, Poopie. Where did I say anything about "technical
persons"? In fact, I specified psycho-acoustic reasons in the part of
my post you stupidly snipped:
"For the innocent: The point of listening tests isn't to discover
which
amp or topology is "better": I already know from comparison with years
in the concert halls which kinds of amps and which topologies I prefer
(Class A1 triodes or trioded pentodes in PP with ESL, and ditto in SET
with horns). The point of tests is to determine why these topologies
affect the emotions differently; psycho-acoustics is probably the last
frontier in audio-electronics."

Graham

If you attention span is shorter than your dick, Poopie, stay out of
my threads. They aren't suitable for soundbiters and idiots.

Andre Jute
"I was at a board meeting for the LA Chapter of the Audio Engineering
Society last night on XM Satellite radio audio and data transmission.
Sadly, we missed you there, and at the SMPTE and Acoustical Society
recent meetings as well. Everyone was asking, 'Where is that wonderful
Andre Jute? The world just doesn't rotate without him...'" -- John
Mayberry, Emmaco

[Andre Jute]

On Nov 4, 5:09 pm, Patrick Turner wrote:
Andre Jute wrote:

On Nov 4, 6:52 am, Patrick Turner wrote:

Musicians do not necessarily have any special hearing abilities.

Yes, they do: they have trained perception. They listen consciously.
Non-audiophiles from the general population cannot even hear the
difference between a boombox played through good speakers and a Class
A PP tube amp played through the same speakers. To them it is all
"nice", useless for tests.

Jeezzuuus! More than half the musos I know are dumb****s.

Of course they are. They play jazz which is by definition not music or
have deafened themselves with amplified guitars. You want to acquaint
yourself with a better class of musician.

A few might have benefitted from being trained musically,
but the majority are not.

All of those in my listening groups had at least ten years of formal
musical training, many or even most since they first started started
school or even before.

The majority are self taught rock/jaz musos, and only a real minority
score well in music reproduction examination tests.

Yech. These are not musicians, Patrick, they are makers of noise.

If I could find enough experienced audiophiles -- defined as having
trained their own aural perception -- available on a regular basis, I
would use them instead. it was just easier in my particular
circumstances to find as many classical musicians as required.

The serious audio clubs in Australia such as the Melbourne Audio Club,
MAC,
and Audiophile Society of NSW, ASON contain enough practised and
experienced ppl whose
opinion can be considered seriously when testing AB set ups in front of
them.
I was a member of ASON for some years and demoed my gear several times
and AB'd it in "sound offs" to see what sounded better.

You're lucky. The local Gramophone Club, the night I went, played old
records on scratchy equipment; they are not audiophiles but music
lovers. Good for them, I say, but useless for my purposes.

The results embarrassed the guy who believed in triodes with no GNFB.

It should also be observed that most audiophiles talk big about their
golden ears but in blind tests have poor discrimination, so that you
first require tests to sort out the good listeners.

Yes, but there were enough good ears in the club to get as good an idea
about the audio quality as you'd ever want.

Melbourne, just by itself, has more people in it than all of Ireland.
It is a lot easier to put together experienced audiophiles there than
here.

That shocked me;
for a while I wondered if the meterheads weren't right, if vanishing
THD numbers aren't the holy grail after all... But you don't want to
hear about the anguish of an open mind.

ASON club members did not hear anything special with gear that had
10 times or lower measured THD/IMD than the tube gear I demoed.

About 1/2 used SS, 1/2 used tube gear. Speakers varied from horns,
generally HQ dynamics, and some ESL.

Sources of the club were also better than average.

And there you have it: serious people, serious gear, experienced ears.

For the innocent: The point of listening tests isn't to discover which
amp or topology is "better": I already know from comparison with years
in the concert halls which kinds of amps and which topologies I prefer
(Class A1 triodes or trioded pentodes in PP with ESL, and ditto in SET
with horns). The point of tests is to determine why these topologies
affect the emotions differently; psycho-acoustics is probably the last
frontier in audio-electronics.

Better usually means sounds better to audiophiles, many of whom couldn't
care a hoot about the measurements.
Better to an engineer means it measures better, and engineers
often are dull emotionally, and incapable of listening to music at all.

"Engineers" aren't my problem, except when they're dumb enough to
think they can tell me my business. I'm interested in the sources of
emotion. Or, as an assistant at one test told a panel member, "Andre
is after the effect of the affect." Poor fellow thought the pretty
bird was swearing at him!

A 100 times betterment in measurements usually does NOT give a 100 time
betterment in sound quality.

Gee, now you tell me, after I wasted my youth chasing AC balance...

Patrick Turner.

Andre Jute
Visit Jute on Amps at http://members.lycos.co.uk/fiultra/
"wonderfully well written and reasoned information
for the tube audio constructor"
John Broskie TubeCAD & GlassWare
"an unbelievably comprehensive web site
containing vital gems of wisdom"
Stuart Perry Hi-Fi News & Record Review

[robert casey]

It isn't clear to me at all how "once can use the heater current",
presumably for some purpose beyond heating the filaments. Can you
please explain more, or provide a reference, or even an outline sketch
of connections.

Andre Jute




Well Andre,
Do you see how the example using a PP output is using half the primary
to cancell DC-generated flux in the core? It takes the same amount of
current as is being passed at idle by the tube we're applying signal
to.
Cheers,
Douglas



As for using that current to run heaters, I could see someone selecting
a version of the desired output tube that draws heater current the same
as the desired quiescent cancellation current. There's the 7695, just
like the 7754 except for heater current of 150ma at 50V. It wants 1100
ohm load resistance, but with plate voltage of 130VDC, that tube isn't
real exciting. But there are other tubes with high heater voltages out
there. BUt what one would do is series string the output tube heater
with its various preamp and driver tube heaters, and pad the shortfall
of heater voltage total with a power resistor. But that resistance
would look like a load to the output tube.

[David R Brooks]

robert casey wrote:


It isn't clear to me at all how "once can use the heater current",
presumably for some purpose beyond heating the filaments. Can you
please explain more, or provide a reference, or even an outline sketch
of connections.

Andre Jute




Well Andre,
Do you see how the example using a PP output is using half the primary
to cancell DC-generated flux in the core? It takes the same amount of
current as is being passed at idle by the tube we're applying signal
to.
Cheers,
Douglas



As for using that current to run heaters, I could see someone selecting
a version of the desired output tube that draws heater current the same
as the desired quiescent cancellation current. There's the 7695, just
like the 7754 except for heater current of 150ma at 50V. It wants 1100
ohm load resistance, but with plate voltage of 130VDC, that tube isn't
real exciting. But there are other tubes with high heater voltages out
there. BUt what one would do is series string the output tube heater
with its various preamp and driver tube heaters, and pad the shortfall
of heater voltage total with a power resistor. But that resistance
would look like a load to the output tube.

And by transformer action, the top of the heater string will carry the
same AC voltage as the OP anode. So the heater-string resistance will be
an unproductive load in parallel with the speaker (as referred to the
OPT primary). If your heaters pull 150mA, a 350V HT means a string
resistance of 2.3kR. In parallel with a reflected load impedance of
several kR, it will eat the lion's share of the OP watts.

OK, while we're on zany ideas, here's another. Have someone wind a PP
transformer, with the two primary halves isolated. Now connect the
"starts" of each winding together, and call that the "centre". So the
free ends would see voltage in phase with each other. Connect the
"centre tap" to a big cap. to ground, the OP anode to one end, and the
other end via a large choke to HT+. Now the DC components in the two
halves cancel, as required. Of course, this is topologically very
similar to a parafeed, but we have eliminated that huge OP capacitor. Ah
well, I did say it was zany...

[Andre Jute]

robert casey wrote:


It isn't clear to me at all how "once can use the heater current",
presumably for some purpose beyond heating the filaments. Can you
please explain more, or provide a reference, or even an outline sketch
of connections.

Andre Jute




Well Andre,
Do you see how the example using a PP output is using half the primary
to cancell DC-generated flux in the core? It takes the same amount of
current as is being passed at idle by the tube we're applying signal
to.
Cheers,
Douglas



As for using that current to run heaters, I could see someone selecting
a version of the desired output tube that draws heater current the same
as the desired quiescent cancellation current. There's the 7695, just
like the 7754 except for heater current of 150ma at 50V. It wants 1100
ohm load resistance, but with plate voltage of 130VDC, that tube isn't
real exciting. But there are other tubes with high heater voltages out
there. BUt what one would do is series string the output tube heater
with its various preamp and driver tube heaters, and pad the shortfall
of heater voltage total with a power resistor. But that resistance
would look like a load to the output tube.

Sure thing, Robert, the series string of heater voltages is vintage
table radio practice. I had the pleasure of studying that one closely
when a couple of weeks ago I redrew John Byrns's "Amplifier without
Power Transformer". I can see how that is a useful topology which can
double as a bleeder for the caps. But I was looking for some really
major advance here, as Douglas Multi-grid first appeared to offer,
some new, stunning way of using the same current as drives the
filaments to make a PP transformer usable as an SE transformer.

The truth is that, above a tiny fraction of the PP current, I have as
little faith in PP trx used for SE as Patrick has. Using PP trannies
for SE is really just a novelty for a gee-whiz a a snowed-in
prototype, not a serious possibility for a permanent amp.

Andre Jute
"I was at a board meeting for the LA Chapter of the Audio Engineering
Society last night on XM Satellite radio audio and data transmission.
Sadly, we missed you there, and at the SMPTE and Acoustical Society
recent meetings as well. Everyone was asking, 'Where is that wonderful
Andre Jute? The world just doesn't rotate without him...'" -- John
Mayberry, Emmaco

[John Byrns]

In article ,
robert casey wrote:


It isn't clear to me at all how "once can use the heater current",
presumably for some purpose beyond heating the filaments. Can you
please explain more, or provide a reference, or even an outline sketch
of connections.

Andre Jute




Well Andre,
Do you see how the example using a PP output is using half the primary
to cancell DC-generated flux in the core? It takes the same amount of
current as is being passed at idle by the tube we're applying signal
to.
Cheers,
Douglas



As for using that current to run heaters, I could see someone selecting
a version of the desired output tube that draws heater current the same
as the desired quiescent cancellation current. There's the 7695, just
like the 7754 except for heater current of 150ma at 50V. It wants 1100
ohm load resistance, but with plate voltage of 130VDC, that tube isn't
real exciting. But there are other tubes with high heater voltages out
there. BUt what one would do is series string the output tube heater
with its various preamp and driver tube heaters, and pad the shortfall
of heater voltage total with a power resistor. But that resistance
would look like a load to the output tube.

That's why you need to add an inductor in series with the "resistance"
so that it doesn't load the output tube. However at that point, since
you have to pay for the choke, you might as well go with a parafeed
connection to keep the DC out of the output transformer, and also reap
the other benefits of that arrangement.


Regards,

John Byrns

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

[John Byrns]

In article
,
David R Brooks wrote:

robert casey wrote:


It isn't clear to me at all how "once can use the heater current",
presumably for some purpose beyond heating the filaments. Can you
please explain more, or provide a reference, or even an outline sketch
of connections.

Andre Jute




Well Andre,
Do you see how the example using a PP output is using half the primary
to cancell DC-generated flux in the core? It takes the same amount of
current as is being passed at idle by the tube we're applying signal
to.
Cheers,
Douglas



As for using that current to run heaters, I could see someone selecting
a version of the desired output tube that draws heater current the same
as the desired quiescent cancellation current. There's the 7695, just
like the 7754 except for heater current of 150ma at 50V. It wants 1100
ohm load resistance, but with plate voltage of 130VDC, that tube isn't
real exciting. But there are other tubes with high heater voltages out
there. BUt what one would do is series string the output tube heater
with its various preamp and driver tube heaters, and pad the shortfall
of heater voltage total with a power resistor. But that resistance
would look like a load to the output tube.

And by transformer action, the top of the heater string will carry the
same AC voltage as the OP anode. So the heater-string resistance will be
an unproductive load in parallel with the speaker (as referred to the
OPT primary). If your heaters pull 150mA, a 350V HT means a string
resistance of 2.3kR. In parallel with a reflected load impedance of
several kR, it will eat the lion's share of the OP watts.

OK, while we're on zany ideas, here's another. Have someone wind a PP
transformer, with the two primary halves isolated. Now connect the
"starts" of each winding together, and call that the "centre". So the
free ends would see voltage in phase with each other. Connect the
"centre tap" to a big cap. to ground, the OP anode to one end, and the
other end via a large choke to HT+. Now the DC components in the two
halves cancel, as required. Of course, this is topologically very
similar to a parafeed, but we have eliminated that huge OP capacitor. Ah
well, I did say it was zany...

Why bother having a special transformer wound, especially since the
whole idea is probably to use an existing PP transformer, your zany idea
should work just as well with a standard wound PP transformer?

However once you have to pay for the "large choke", you might as well
bite the bullet and pop for the parafeed capacitor too, and use the
actual parafeed connection which gives improved power supply rejection,
reducing the hum level at the speaker.


Regards,

John Byrns

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

[Arny Krueger]

"Andre Jute" wrote in message
oups.com...
On Nov 4, 6:52 am, Patrick Turner wrote:

Musicians do not necessarily have any special hearing abilities.

They are also not immune to hearing damage, even occupationally-related.

Yes, they do: they have trained perception.

But they are not unique in that regard.

Also, what they listen for is not necessarily the same as what you listen
for when you listen for differences between audio products.

They listen consciously.

That's hardly unique to musicians.

Non-audiophiles from the general population cannot even hear the
difference between a boombox played through good speakers and a Class
A PP tube amp played through the same speakers.

Boomboxes rarely if ever have speaker outputs, so this is a nonsense
statement.

To them it is all "nice", useless for tests.

I've done enough listening tests with non-audiophiles and non-musicans to be
careful about putting them all down.

If I could find enough experienced audiophiles -- defined as having
trained their own aural perception -- available on a regular basis, I
would use them instead.

Been there done that. BTW, one good way for audiophiles to train their
perceptions is to spend some time actually listening for differences that
are known to be audible, but perhaps neer the margin of audibility.

it was just easier in my particular
circumstances to find as many classical musicians as required.

I've definately worked with classical musicans with serious ear damage.
While they generally have good acuity when it comes to tone and timing,
there's a lot that goes wrong in audio that is independent of that.

It should also be observed that most audiophiles talk big about their
golden ears but in blind tests have poor discrimination, so that you
first require tests to sort out the good listeners.

It is true that the high end audio industry pretty much trains audiophiles
to have a very optimistic view of their hearing acuity.

That shocked me;
for a while I wondered if the meterheads weren't right, if vanishing
THD numbers aren't the holy grail after all... But you don't want to
hear about the anguish of an open mind.

No danger of hearing about the anguish of an open mind from Jute, his
sockpuppets, and his fellow-travelers.

For the innocent: The point of listening tests isn't to discover which
amp or topology is "better": I already know from comparison with years
in the concert halls which kinds of amps and which topologies I prefer
(Class A1 triodes or trioded pentodes in PP with ESL, and ditto in SET
with horns).

Thanks for admitting that you already know the right answers, Jute.

The point of tests is to determine why these topologies
affect the emotions differently; psycho-acoustics is probably the last
frontier in audio-electronics.

So far I have yet to see a credible statement about psychoacoustics from
you, Jute.

Andre Jute
"I was at a board meeting for the LA Chapter of the Audio Engineering
Society last night on XM Satellite radio audio and data transmission.
Sadly, we missed you there, and at the SMPTE and Acoustical Society
recent meetings as well. Everyone was asking, 'Where is that wonderful
Andre Jute? The world just doesn't rotate without him...'" -- John
Mayberry, Emmaco

More likely, they were asking why XP used to sound so much better, but now
generally sounds like crap. The answer is bandwidth and what happens to
audio when you try to route twice as many channels through the same
bandwidth.

[Dave]

"Andre Jute" wrote in message
ups.com...

).

Sure. I don't know how you will build it. I have to assume you know
enough to ground your chassis! I also assume you will use a three-
point (IEC) grounded plug, not those dangerous American two-point
things.


Isn't there a rationale floating around out there that says that if you
mains ground every piece of audio gear, you'll end up with ground loops?
Wouldn't tying your signal ground to mains earth potentially amplify any
noise on the ground circuit, i.e. hum from your fridge motor and everything
else?

[Eeyore]

Dave wrote:

"Andre Jute" wrote

Sure. I don't know how you will build it. I have to assume you know
enough to ground your chassis! I also assume you will use a three-
point (IEC) grounded plug, not those dangerous American two-point
things.

Isn't there a rationale floating around out there that says that if you
mains ground every piece of audio gear, you'll end up with ground loops?

You mean hum ? Depends on the existence or otherwise of any magnetic fields and
leakage currents.


Wouldn't tying your signal ground to mains earth potentially amplify any
noise on the ground circuit, i.e. hum from your fridge motor and everything
else?

NO. That simply illustrates a very poor understanding of audio circuits.

Graham

[robert casey]

And by transformer action, the top of the heater string will carry the
same AC voltage as the OP anode. So the heater-string resistance will be
an unproductive load in parallel with the speaker (as referred to the
OPT primary). If your heaters pull 150mA, a 350V HT means a string
resistance of 2.3kR. In parallel with a reflected load impedance of
several kR, it will eat the lion's share of the OP watts.


I suppose one could build a constant current sucker circuit to make it
look like a very high impedance on that transformer winding. But at
this point (if not already) we're piling so much silliness into this as
to be absurd. As well as so much cost as to make it better putting that
cost into a real single ended transformer in the first place.

[Multi-grid]

On Nov 4, 4:43 pm, Andre Jute wrote:
On Nov 4, 12:02 pm, Multi-grid wrote:





On Nov 4, 3:32 am, Andre Jute wrote:

Jute:

Casey:
One could use a push-pull output transformer om a single-ended design,
if you also send a steady DC current (equal to the quiescent class A
current of the tube) thru the other half of the primary from the
centertap (connected to B+) to the unused side, via most likely a power
resistor to ground. But that's rather wasteful of the power you went to

Multi-grid:

hey-Hey!!!,
What you describe is one of the methods to do DC current cancelling.
The other half of the PP primary is straightforward to implement, it
takes the same current as the tube idling opposite it.

Okay, but wasteful.

One can also use heater current. Best SE amp I ever heard was a 50W
monster that had a piddling little output TX. Through a special
winding went the required 25A of heater current for that valve...no
intentional gap needed anymore.
cheers,
Douglas

It isn't clear to me at all how "once can use the heater current",
presumably for some purpose beyond heating the filaments. Can you
please explain more, or provide a reference, or even an outline sketch
of connections.

Andre Jute

- Show quoted text -

Well Andre,
Do you see how the example using a PP output is using half the primary
to cancell DC-generated flux in the core? It takes the same amount of
current as is being passed at idle by the tube we're applying signal
to.
Cheers,
Douglas

Sure, standard stuff, but that's not my question. That is about
quiescent plate current. I want you to show me how this works:

Through a special
winding went the required 25A of heater current for that valve...no
intentional gap needed anymore.

They're your words and they don't make sense to me. Take all the space
you need. Please feel free to treat me as a total ignoramus and
explain in words of one syllable, with all the tees crossed and all
the eyes dotted so that there can be no misunderstanding. A schematic
is always good to avoid misunderstanding.

Andre Jute
Visit Jute on Amps athttp://members.lycos.co.uk/fiultra/
"wonderfully well written and reasoned information
for the tube audio constructor"
John Broskie TubeCAD & GlassWare
"an unbelievably comprehensive web site
containing vital gems of wisdom"
Stuart Perry Hi-Fi News & Record Review- Hide quoted text -

- Show quoted text -

What don't you 'get'? Think some more. Think 'ampere-turns'. Take a
primary of two to three thousand turns, and run 100 mA through it. Put
this coil around a minimum gap/alternate stacked E-I or cut C-core.
What happens to the flux?

Got an answer yet?

Take another winding, and run the filament current through it. It is
substantially larger than 0.1 Ampere( actually 25 A was my example).
You should energize the correct end of this winding, eh?

Now what is going on?

Given a given coil geometry and interleave, which will have more
injurious parasitic stuff like interwinding capacitance and leakage L,
smaller core or bigger cored designs?

and quoted from Mr.Burns:
Andre, you are wasting your time with Multi-grid, you won't get any
answers from him as he hasn't yet reached the point in his studies
where
he can even understand the question.

Regards,
John Byrns

Now John,
It amazes me that you would actually expect me to answer given your
insults and slights. I don't see the need to answer in much detail to
folks who claim such deep understanding of tube circuit behaviour and
design. Besides, it is more fun for you to figure it out yourself, and
less work for me. Behave yourself.


There is additional issues with parafeeding PP outputs, they are
designed( if any good ) to have the CT at AC ground. Using them SE and
full length puts something besides AC ground at the CT, yes?
cheers,
Douglas

[Dave]

"Eeyore" wrote in message
...


Dave wrote:

"Andre Jute" wrote

Sure. I don't know how you will build it. I have to assume you know
enough to ground your chassis! I also assume you will use a three-
point (IEC) grounded plug, not those dangerous American two-point
things.

Isn't there a rationale floating around out there that says that if you
mains ground every piece of audio gear, you'll end up with ground loops?

You mean hum ? Depends on the existence or otherwise of any magnetic
fields and
leakage currents.



Okay, let's suppose for the sake of arguement that there is either AC or DC
current on the mains ground. Would you get hum? What might be any other
effects?

Wouldn't tying your signal ground to mains earth potentially amplify any
noise on the ground circuit, i.e. hum from your fridge motor and
everything
else?

NO. That simply illustrates a very poor understanding of audio circuits.

Then why do many designers go to the effort of isolating signal ground? Are
you saying noise on the mains ground will have no effect on the output?

Dave

[John Byrns]

In article . com,
Multi-grid wrote:

On Nov 4, 4:43 pm, Andre Jute wrote:

They're your words and they don't make sense to me. Take all the space
you need. Please feel free to treat me as a total ignoramus and
explain in words of one syllable, with all the tees crossed and all
the eyes dotted so that there can be no misunderstanding. A schematic
is always good to avoid misunderstanding.

What don't you 'get'? Think some more. Think 'ampere-turns'. Take a
primary of two to three thousand turns, and run 100 mA through it. Put
this coil around a minimum gap/alternate stacked E-I or cut C-core.
What happens to the flux?

Got an answer yet?

Take another winding, and run the filament current through it. It is
substantially larger than 0.1 Ampere( actually 25 A was my example).
You should energize the correct end of this winding, eh?

Andre, notice how Multi-grid is avoiding your question, and being
evasive about how this scheme actually works. It is straight forward to
use the filament current to provide the bias to the core to offset the
current from the amplifier tube, or any other current for that matter,
as long as the number of ampere-turns is the same as in the active
primary, as Multi-grid points out. Unfortunately the issue that
Multi-grid doesn't want to deal with, or can't, is that a substantial
portion of the audio power generated by the active tube is dissipated
across the filament resistance of the tube and never makes it to the
speaker.

The bottom line is that this circuit doesn't work very well when built
as Multi-grid describes it. The problem can be dealt with, but dealing
with it adds considerable extra cost, which makes one wonder why anyone
in their right mind would take this approach to building an amplifier in
the first place?


Regards,

John Byrns

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

[Eeyore]

Dave wrote:

"Eeyore" wrote
Dave wrote:
"Andre Jute" wrote

Sure. I don't know how you will build it. I have to assume you know
enough to ground your chassis! I also assume you will use a three-
point (IEC) grounded plug, not those dangerous American two-point
things.

Isn't there a rationale floating around out there that says that if you
mains ground every piece of audio gear, you'll end up with ground loops?

You mean hum ? Depends on the existence or otherwise of any magnetic
fields and leakage currents.


Okay, let's suppose for the sake of arguement that there is either AC or DC
current on the mains ground.

First off forget DC. It's very unlikely anyway and won't affect the audio.

Next, what do you mean by "there is AC current on the mains ground" ? To be
honest it sounds like you don't know what you mean. What does 'on a ground' mean
? 'ON' is the wrong word for a current anyway. You may have current IN a
conductor but not ON one. You can however have a voltage ON a conductor. Do you
mean that the voltage at the ground connection at the wall socket isn't actually
a 'pure' ground ?


Would you get hum? What might be any other effects?

You'll get hum in a configuration where multiple pieces of audio equipment share
BOTH a mains earth AND unbalanced signal interconnects that also use the earth
for the low side of the signal **IF** and **only IF** those loops created by the
interconnects and mains wiring are subject to an alternating magnetic field OR
if any of those pieces of equipment has a leakage current to earth that then
flows in the shield/screens of the interconnects instead of flowing ONLY in the
ground wire of the mains supply.

Other effects would include susceptibility to other tyres of magnetic field such
as created by the scan coils of a CRT based TV or PC monitor.


Wouldn't tying your signal ground to mains earth potentially amplify any
noise on the ground circuit, i.e. hum from your fridge motor and
everything else?

NO. That simply illustrates a very poor understanding of audio circuits.

Then why do many designers go to the effort of isolating signal ground?

A lot of it is 'tradition' and a lot of tradition is very bad practice too. You
don't see this in professional equipment.


Are you saying noise on the mains ground will have no effect on the output?

If ALL the equipment is 'riding' on some voltage on the ground/earth connection
equally, i.e. it's not a perfect ground it'll still perform just fine. The
'ground' is for the most part simply some reference potential for the purposes
of the audio circuitry. As long as EVERYTHING shares that same potential, there
will be NO adverse effect.

Graham

[Dave]

"Eeyore" wrote in message
...


Next, what do you mean by "there is AC current on the mains ground" ? To
be
honest it sounds like you don't know what you mean. What does 'on a
ground' mean
? 'ON' is the wrong word for a current anyway. You may have current IN a
conductor but not ON one. You can however have a voltage ON a conductor.
Do you
mean that the voltage at the ground connection at the wall socket isn't
actually
a 'pure' ground ?


What I meant was suppose there was another device on the same circuit (i.e.
common ground wiring) which was leaking current INto the ground wiring. But
I see what you mean below when you say that it won't matter as long as ALL
of the pieces of equipment are aat the same elevated ground potential.


Would you get hum? What might be any other effects?

You'll get hum in a configuration where multiple pieces of audio equipment
share
BOTH a mains earth AND unbalanced signal interconnects that also use the
earth
for the low side of the signal **IF** and **only IF** those loops created
by the
interconnects and mains wiring are subject to an alternating magnetic
field OR
if any of those pieces of equipment has a leakage current to earth that
then
flows in the shield/screens of the interconnects instead of flowing ONLY
in the
ground wire of the mains supply.

Other effects would include susceptibility to other tyres of magnetic
field such
as created by the scan coils of a CRT based TV or PC monitor.


Wouldn't tying your signal ground to mains earth potentially amplify
any
noise on the ground circuit, i.e. hum from your fridge motor and
everything else?

NO. That simply illustrates a very poor understanding of audio
circuits.

Then why do many designers go to the effort of isolating signal ground?

A lot of it is 'tradition' and a lot of tradition is very bad practice
too. You
don't see this in professional equipment.


Are you saying noise on the mains ground will have no effect on the
output?

If ALL the equipment is 'riding' on some voltage on the ground/earth
connection
equally, i.e. it's not a perfect ground it'll still perform just fine. The
'ground' is for the most part simply some reference potential for the
purposes
of the audio circuitry. As long as EVERYTHING shares that same potential,
there
will be NO adverse effect.


Thanks. that was clear, concise, and answered my questions fully. At one
time I had considered building some balanced XLR adaptors to convert my
existing equipment outputs. If I am having no hum issues, is it your
opinion that this would be a waste of time, or, as many "serious
audiophiles" insist, do the balanced interconnects improve the sound in any
way?

Dave

[Eeyore]

Dave wrote:

"Eeyore" wrote

Next, what do you mean by "there is AC current on the mains ground" ? To
be honest it sounds like you don't know what you mean. What does 'on a
ground' mean ? 'ON' is the wrong word for a current anyway. You may have
current IN a
conductor but not ON one. You can however have a voltage ON a conductor.
Do you mean that the voltage at the ground connection at the wall socket
isn't
actually a 'pure' ground ?


What I meant was suppose there was another device on the same circuit (i.e.
common ground wiring) which was leaking current INto the ground wiring. But
I see what you mean below when you say that it won't matter as long as ALL
of the pieces of equipment are aat the same elevated ground potential.

You got it.

snip

If ALL the equipment is 'riding' on some voltage on the ground/earth
connection equally, i.e. it's not a perfect ground it'll still perform just
fine. The
'ground' is for the most part simply some reference potential for the
purposes of the audio circuitry. As long as EVERYTHING shares that same
potential,
there will be NO adverse effect.

Thanks. that was clear, concise, and answered my questions fully.

Thank you. I did try to cover it fully.


At one time I had considered building some balanced XLR adaptors to convert my

existing equipment outputs. If I am having no hum issues, is it your
opinion that this would be a waste of time, or, as many "serious
audiophiles" insist, do the balanced interconnects improve the sound in any
way?

Balanced audio does NOT 'improve the sound' per se. Its main function is to
reduce or effectively eliminate equipment interconnecting problems. If you have
no such problems, then you don't need to change to balanced connections. Most
'audiophools' haven't a clue btw. They imagine it's magic not science and
technology.

Graham

[Multi-grid]

On Nov 6, 12:42 am, John Byrns wrote:
In article . com,





Multi-grid wrote:
On Nov 4, 4:43 pm, Andre Jute wrote:

They're your words and they don't make sense to me. Take all the space
you need. Please feel free to treat me as a total ignoramus and
explain in words of one syllable, with all the tees crossed and all
the eyes dotted so that there can be no misunderstanding. A schematic
is always good to avoid misunderstanding.

What don't you 'get'? Think some more. Think 'ampere-turns'. Take a
primary of two to three thousand turns, and run 100 mA through it. Put
this coil around a minimum gap/alternate stacked E-I or cut C-core.
What happens to the flux?

Got an answer yet?

Take another winding, and run the filament current through it. It is
substantially larger than 0.1 Ampere( actually 25 A was my example).
You should energize the correct end of this winding, eh?

Andre, notice how Multi-grid is avoiding your question, and being
evasive about how this scheme actually works. It is straight forward to
use the filament current to provide the bias to the core to offset the
current from the amplifier tube, or any other current for that matter,
as long as the number of ampere-turns is the same as in the active
primary, as Multi-grid points out. Unfortunately the issue that
Multi-grid doesn't want to deal with, or can't, is that a substantial
portion of the audio power generated by the active tube is dissipated
across the filament resistance of the tube and never makes it to the
speaker.

The bottom line is that this circuit doesn't work very well when built
as Multi-grid describes it. The problem can be dealt with, but dealing
with it adds considerable extra cost, which makes one wonder why anyone
in their right mind would take this approach to building an amplifier in
the first place?

Regards,

John Byrns

--
Surf my web pages at, http://fmamradios.com/- Hide quoted text -

- Show quoted text -

Well John I've made it plain that I am not going to hand this out. It
isn't any fun for you, and it is too much work for me. So get with it
if you can. Just remember, I know your belief or understading isn't
required, I've seen it in action.

You have yet to do anything which deserves my indulgence of your lazy
and closed mind. Behave yourself.
cheers,
Douglas

I'll give you a hint: Think about the power, you've come to an
incorrect conclusion. See if you can find it.

[Andre Jute]

On Nov 5, 10:42 pm, John Byrns wrote:
In article . com,



Multi-grid wrote:
On Nov 4, 4:43 pm, Andre Jute wrote:

They're your words and they don't make sense to me. Take all the space
you need. Please feel free to treat me as a total ignoramus and
explain in words of one syllable, with all the tees crossed and all
the eyes dotted so that there can be no misunderstanding. A schematic
is always good to avoid misunderstanding.

What don't you 'get'? Think some more. Think 'ampere-turns'. Take a
primary of two to three thousand turns, and run 100 mA through it. Put
this coil around a minimum gap/alternate stacked E-I or cut C-core.
What happens to the flux?

Got an answer yet?

Take another winding, and run the filament current through it. It is
substantially larger than 0.1 Ampere( actually 25 A was my example).
You should energize the correct end of this winding, eh?

Andre, notice how Multi-grid is avoiding your question, and being
evasive about how this scheme actually works. It is straight forward to
use the filament current to provide the bias to the core to offset the
current from the amplifier tube, or any other current for that matter,
as long as the number of ampere-turns is the same as in the active
primary, as Multi-grid points out.

Yes, but that means a specially wound transformer, a vast expense in
the context of trying to use a junkbox or at least existing PP
transformer for SE. Plus a cap and probably a choke that Multi-Cuddles
doesn't mention, and soon you're into real money. This isn't an
innovation, this is a kludge to bodge right another kludge.

Unfortunately the issue that
Multi-grid doesn't want to deal with, or can't, is that a substantial
portion of the audio power generated by the active tube is dissipated
across the filament resistance of the tube and never makes it to the
speaker.

Yah. This is why I wrote to Robert Casey that I have zero faith in
these heathrobinson schemes because I have never managed to run more
than a tiny fraction of the PP current through a PP trx being used for
SE, not if I wanted a result that satisfied my noise criteria anyway.
It's a novelty, not a circuit.

The bottom line is that this circuit doesn't work very well when built
as Multi-grid describes it. The problem can be dealt with, but dealing
with it adds considerable extra cost, which makes one wonder why anyone
in their right mind would take this approach to building an amplifier in
the first place?

At the time that Bottlehead took his Electronic Tonalities all-
parafeed, he said it was because it sounded better. I believe him,
that it sounds better to him and his circle of very competent DIYers.
But I like conservative engineering, especially KISS. I'd rather spend
the same money that goes into parafeed on a proper SE output and just
put the bloody current through the primary.

Regards,

John Byrns

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

Oh well, there goes another perpetual motion machine into the free-
lunch chute to infinity.

Andre Jute
Visit Jute on Amps at http://members.lycos.co.uk/fiultra/
"wonderfully well written and reasoned information
for the tube audio constructor"
John Broskie TubeCAD & GlassWare
"an unbelievably comprehensive web site
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[Andre Jute]

On Nov 5, 7:37 pm, "Dave" wrote:
"Andre Jute" wrote in message

ups.com...



).

Sure. I don't know how you will build it. I have to assume you know
enough to ground your chassis! I also assume you will use a three-
point (IEC) grounded plug, not those dangerous American two-point
things.

Isn't there a rationale floating around out there that says that if you
mains ground every piece of audio gear, you'll end up with ground loops?

Don't overcomplicate matters when you're starting out. You're not
building "every piece of audio gear". You're building a power amp that
will have exposed metal and high voltages. You shouldn't leave it
floating. Therefore you must ground it.

If you ground it as I suggest, and if your wiring is tidy (short,
cross at right angles, well enough separated -- air is the best
dielectric), then you will be surprised at how little rubbish you pick
up either out of the air or on the mains wire. The ground circuit that
I suggest, if laid out like the one I gave a URL for, will have all 0V
lines connected to a star at the bottom of the bleeder, a short line
from there to the mains ground at the 3-point plug, and a short line
from the mains ground to a chassis connection right next to the plug.
There is very little to loop here. It would in fact be very difficult
for a potential difference to arise in the ground wiring in such a
scheme. That is why I suggest it; it is part of the silence of the
amp!

Wouldn't tying your signal ground to mains earth potentially amplify any
noise on the ground circuit, i.e. hum from your fridge motor and everything
else?

Forget it until it happens, then you can fix it. I used to put a mains
rated cap across the mains but no longer do it and don't show it on
new circuits because I know of nobody who found it necessary (and it
is dangerous to get that cap wrong). If and when it happens, you buy a
filter.

Andre Jute
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