[Phil Allison[_3_]]

"John Byrns"

A couple of questions for Mr. Turner, with respect to the Bean Counters
employed
by Acoustical/QUAD back in the days when the QUAD II was being designed.


** The justifiably very famous QUAD II power amplifier was designed by
Peter Walker in the early 1950s, while the whole UK was still suffering the
aftermath of WW2 and in a state of poverty because the country's economy was
deeply in debt to the USA.

Despite this, the QUAD II was built with the highest quality parts available
at the time - plus 3 superb wound components his firm made specially for
the amp.

Merely to keep production costs within sanity, Peter designed his new amp to
use as few components as possible - unlike most of his competitors.

He chose GEC KT66s because they were the most linear tubes then available
for an audio power amp and EF86s as they were cheap, linear and had plenty
of voltage gain.

He also chose paper in oil filter caps in preference to electrolytics to
give the amp a long life.

The completed amp had exceptionally low THD (circa 0.1%), was internal
adjustment free and very stable - although the even more famous Quad ESL
speaker that would partner it was still years off - as was stereo
reproduction.

The QUAD II is "penny pinched" in the just same way that a Shakespeare
sonnet is rather short on words.

While the Turneroid fool is a self obsessed, conceited utter ass.




.... Phil

[Patrick Turner]

On Jun 9, 10:20*pm, "Phil Allison" wrote:
"John Byrns"



A couple of questions for Mr. Turner, with respect to the Bean Counters
employed
by Acoustical/QUAD back in the days when the QUAD II was being designed..

** *The justifiably very famous QUAD II *power amplifier was designed by
Peter Walker in the early 1950s, while the whole UK was still suffering the
aftermath of WW2 and in a state of poverty because the country's economy was
deeply in debt to the USA.

Despite this, the QUAD II was built with the highest quality parts available
at the time *- *plus 3 superb wound components his firm made specially for
the amp.

Merely to keep production costs within sanity, Peter designed his new amp to
use as few components as possible - *unlike most of his competitors.

He chose GEC KT66s because they were the most linear tubes then available
for an audio power amp and EF86s as they were cheap, linear and had plenty
of voltage gain.

He also chose paper in oil filter caps in preference to electrolytics to
give the amp a long life.

The completed amp had exceptionally low THD (circa 0.1%), was internal
adjustment free and very stable *- *although the even more famous Quad ESL
speaker that would partner it was still years off - as was stereo
reproduction.

The QUAD II *is "penny pinched" *in the just same way that a Shakespeare
sonnet is rather short on words.

While the Turneroid fool is a self obsessed, conceited utter ass.

The Quad amps were a bean counter's delight, an exercize in Quality
Minimization to allow the British to have amplifiers within their very
limited financial reach as you so rightly point out. The PT has quite
high winding resistance, the OPT has appallingly high winding
resistances, but the screen filter choke is OK and its 600 ohms dcr is
fine because of the low screen Idc involved which includes Idc for the
truly horrid Type 22 control unit and AM tuner, quite good, and FM
tuner, not bad.

Where have your powers of careful appraisal dissappeared to Phil?

KT66 were just beam tetrodes, nothin special, and so were EF86, just
miniturised versions of average low quality pentodes with low gm which
forced high RL values including pathetic 680k bias R for KT66.
I do not want to repeat the long long list of Quad-II shortcomings
which you want now to ignore.

Just because " plus 3 superb wound components his firm made specially
for the amp " as you suggest, it does not mean they were indeed
special at all. It just means a gang of Poms who were not shot dead in
WW2 could make the gear OK which meant as cheaply as possible for the
public and after throwing away RDH4.

John asked me how I would have made Quad had I been in charge of Quad
in 1950. Obviously a silly but humerous question, but one I have
answered fully and without a drop of insult.

Up to your old tricks? Nice for 3 posts and then you turn into the one
person who has the very worst record for unbridled and unwanted
incorrect and repeated bullying and arsolic behaviour anyone has known
during the last 10 years.

Let me know when you have completed work on your website which tells
folks how to build better amps than most. Have you designed and sold
many amps which people prefer to Quad-II standard? I thought not.

Quad sure made and sold a lotta stuff, but most couldn't afford any of
it, and they settled for whatever else they could find or make for
themselves, and I know many who don't like Quad ESL speakers which
were probably Quad's real achievement. Why didn't everyone buy Quad
stuff?

Patrick Turner.



... *Phil

[Patrick Turner]

On Jun 10, 11:17*am, Patrick Turner wrote:
On Jun 9, 10:20*pm, "Phil Allison" wrote:





"John Byrns"

A couple of questions for Mr. Turner, with respect to the Bean Counters
employed
by Acoustical/QUAD back in the days when the QUAD II was being designed.

** *The justifiably very famous QUAD II *power amplifier was designed by
Peter Walker in the early 1950s, while the whole UK was still suffering the
aftermath of WW2 and in a state of poverty because the country's economy was
deeply in debt to the USA.

Despite this, the QUAD II was built with the highest quality parts available
at the time *- *plus 3 superb wound components his firm made specially for
the amp.

Merely to keep production costs within sanity, Peter designed his new amp to
use as few components as possible - *unlike most of his competitors.

He chose GEC KT66s because they were the most linear tubes then available
for an audio power amp and EF86s as they were cheap, linear and had plenty
of voltage gain.

He also chose paper in oil filter caps in preference to electrolytics to
give the amp a long life.

The completed amp had exceptionally low THD (circa 0.1%), was internal
adjustment free and very stable *- *although the even more famous Quad ESL
speaker that would partner it was still years off - as was stereo
reproduction.

The QUAD II *is "penny pinched" *in the just same way that a Shakespeare
sonnet is rather short on words.

While the Turneroid fool is a self obsessed, conceited utter ass.

The Quad amps were a bean counter's delight, an exercize in Quality
Minimization to allow the British to have amplifiers within their very
limited financial reach as you so rightly point out. The PT has quite
high winding resistance, the OPT has appallingly high winding
resistances, but the screen filter choke is OK and its 600 ohms dcr is
fine because of the low screen Idc involved which includes Idc for the
truly horrid Type 22 control unit and AM tuner, quite good, and FM
tuner, not bad.

Where have your powers of careful appraisal dissappeared to Phil?

KT66 were just beam tetrodes, nothin special, and so were EF86, just
miniturised versions of average low quality pentodes with low gm which
forced high RL values including pathetic 680k bias R for KT66.
I do not want to repeat the long long list of Quad-II shortcomings
which you want now to ignore.

Just because " plus 3 superb wound components his firm made specially
for the amp " as you suggest, it does not mean they were indeed
special at all. It just means a gang of Poms who were not shot dead in
WW2 could make the gear OK which meant as cheaply as possible for the
public and after throwing away RDH4.

John asked me how I would have made Quad had I been in charge of Quad
in 1950. Obviously a silly but humerous question, but one I have
answered fully and without a drop of insult.

Up to your old tricks? Nice for 3 posts and then you turn into the one
person who has the very worst record for unbridled and unwanted
incorrect and repeated bullying and arsolic behaviour anyone has known
during the last 10 years.

Let me know when you have completed work on your website which tells
folks how to build better amps than most. Have you designed and sold
many amps which people prefer to Quad-II standard? I thought not.

Quad sure made and sold a lotta stuff, but most couldn't afford any of
it, and they settled for whatever else they could find or make for
themselves, and I know many who don't like Quad ESL speakers which
were probably Quad's real achievement. Why didn't everyone buy Quad
stuff?

Patrick Turner.





... *Phil- Hide quoted text -

- Show quoted text -- Hide quoted text -

- Show quoted text -

[Andre Jute[_2_]]

On Jun 9, 1:20*pm, "Phil Allison" wrote:
"John Byrns"



A couple of questions for Mr. Turner, with respect to the Bean Counters
employed
by Acoustical/QUAD back in the days when the QUAD II was being designed..

** *The justifiably very famous QUAD II *power amplifier was designed by
Peter Walker in the early 1950s, while the whole UK was still suffering the
aftermath of WW2 and in a state of poverty because the country's economy was
deeply in debt to the USA.

Despite this, the QUAD II was built with the highest quality parts available
at the time *- *plus 3 superb wound components his firm made specially for
the amp.

Merely to keep production costs within sanity, Peter designed his new amp to
use as few components as possible - *unlike most of his competitors.

He chose GEC KT66s because they were the most linear tubes then available
for an audio power amp and EF86s as they were cheap, linear and had plenty
of voltage gain.

He also chose paper in oil filter caps in preference to electrolytics to
give the amp a long life.

The completed amp had exceptionally low THD (circa 0.1%), was internal
adjustment free and very stable *- *although the even more famous Quad ESL
speaker that would partner it was still years off - as was stereo
reproduction.

The QUAD II *is "penny pinched" *in the just same way that a Shakespeare
sonnet is rather short on words.

While the Turneroid fool is a self obsessed, conceited utter ass.

... *Phil

I agree with Phil. Patrick has waffled all over the place, and
wriggled and weaseled, and hasn't answered John's question, because he
can't, because even with modern knowledge he can't do better than
Peter Walker did sixty years ago. Here is John's question as a
reminder:

"...what sort of design you would produce if you were employed by QUAD
in the day and were tasked with designing the "QUAD II" while
maintaing the same factory cost as the actual QUAD II. Any comments
on what you would have done differently?"

Everything Patrick wants to do would have cost more money or required
parts then not available.

Twenty-twenty hindsight is a wonderful thing, but a design talent on
the day it isn't, never mind genius like Peter Walker's.

Andre Jute
Visit Jute on Amps at
http://www.audio-talk.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

[Phil Allison[_3_]]

"Andre Jute"

** The justifiably very famous QUAD II power amplifier was designed by
Peter Walker in the early 1950s, while the whole UK was still suffering
the
aftermath of WW2 and in a state of poverty because the country's economy
was
deeply in debt to the USA.

Despite this, the QUAD II was built with the highest quality parts
available
at the time - plus 3 superb wound components his firm made specially for
the amp.

Merely to keep production costs within sanity, Peter designed his new amp
to
use as few components as possible - unlike most of his competitors.

He chose GEC KT66s because they were the most linear tubes then available
for an audio power amp and EF86s as they were cheap, linear and had plenty
of voltage gain.

He also chose paper in oil filter caps in preference to electrolytics to
give the amp a long life.

The completed amp had exceptionally low THD (circa 0.1%), was internal
adjustment free and very stable - although the even more famous Quad ESL
speaker that would partner it was still years off - as was stereo
reproduction.

The QUAD II is "penny pinched" in the just same way that a Shakespeare
sonnet is rather short on words.

While the Turneroid fool is a self obsessed, conceited utter ass.

... Phil

I agree with Phil.


** Wise man, is our Andre.

How the heck are you ?



.... Phil

[Patrick Turner]

On Jun 10, 12:06*pm, Andre Jute wrote:
On Jun 9, 1:20*pm, "Phil Allison" wrote:





"John Byrns"

A couple of questions for Mr. Turner, with respect to the Bean Counters
employed
by Acoustical/QUAD back in the days when the QUAD II was being designed.

** *The justifiably very famous QUAD II *power amplifier was designed by
Peter Walker in the early 1950s, while the whole UK was still suffering the
aftermath of WW2 and in a state of poverty because the country's economy was
deeply in debt to the USA.

Despite this, the QUAD II was built with the highest quality parts available
at the time *- *plus 3 superb wound components his firm made specially for
the amp.

Merely to keep production costs within sanity, Peter designed his new amp to
use as few components as possible - *unlike most of his competitors.

He chose GEC KT66s because they were the most linear tubes then available
for an audio power amp and EF86s as they were cheap, linear and had plenty
of voltage gain.

He also chose paper in oil filter caps in preference to electrolytics to
give the amp a long life.

The completed amp had exceptionally low THD (circa 0.1%), was internal
adjustment free and very stable *- *although the even more famous Quad ESL
speaker that would partner it was still years off - as was stereo
reproduction.

The QUAD II *is "penny pinched" *in the just same way that a Shakespeare
sonnet is rather short on words.

While the Turneroid fool is a self obsessed, conceited utter ass.

... *Phil

I agree with Phil. Patrick *has waffled all over the place, and
wriggled and weaseled, and hasn't answered John's question, because he
can't, because even with modern knowledge he can't do better than
Peter Walker did sixty years ago. Here is John's question as a
reminder:

"...what sort of design you would produce if you were employed by QUAD
in the day and were tasked with designing the "QUAD II" while
maintaing the same factory cost as the actual QUAD II. *Any comments
on what you would have done differently?"

Everything Patrick wants to do would have cost more money or required
parts then not available.

Twenty-twenty hindsight is a wonderful thing, but a design talent on
the day it isn't, never mind genius like Peter Walker's.


Never for a minute did I ever expect to get any support on my anti-
sacred cow stance. From my greatest critics such as Phil I see almost
no creativity at all with regard to amplifier design.

Walker seems more like a stoical battler to me rather than a genious.

Fact is, he through away the book on his Quad-II OPT. Its a peice of
****. **** is a mighty fine fertilizer if used wisely though, and I
have always found the Acoustical connection excellent sounding as well
as good measuring. I've implemented the Acoustical far better than
Walker ever did. He went to solid state like everyone else did instead
of staying with tubes. There were many who thought hi-fi suffered from
this indistry wide move. Walker invented current dumping, and many
thought that was one great big bodge if ever there was one. I raise my
hat to all those of the past who tried to use tubes and from my view I
see what I know works best so I use it. In my mind there is no god, or
spirits or sacred cows I must katow to; all ideas worth anything must
offer the best function and fidelity, and you most surely can get
better hi-fi by ignoring the Quad-II EF86 input stages. The Williamson
is much better, and in a recent post I said so and gave details why
Walker should have adopted Williamsons's front end. To make the
Williamson front end for Quad-II does not involve an expensive
negative rail with extra tube and socket not need any parts I use now
which were yet to be invented in 1950.

Anyway, if PW hadn't used the Acoustical, someone else would have.
McIntosh certainly went a lot further down the road of local NFB in
the OP stage. Genius to me is confined to very few. Albert Einstein
may have been genious, but Walker, no, he just kept on battling with
everything and as my posts point out there was an enormous amount of
human bull**** going on in the UK while he tried to make something
special in tube amplifiers but failed. Yeah, failed, but there is no
dishonour; he gave what he could, and hardly anyone wanted anything
better; they were not going to pay more for something better, so who
*also* is to blame for the shortcomings of Quad-II? The British Public
of course, thousands of 'em, they wouldn't know quality if it bit 'em
on their bums. I do wonder how receptive Walker was to well made
suggestions and criticisms. I think his abilities matured with the
Quad 405 which remains as good a sounding SS amp as any made now. But
gee, its so easy to get to that level of performance in SS. Just read
Douglas Self and Linsely Hood and others.

PW's ESL were very fine things, but alas, not to everyone's taste and
I know many who dislike ESL speakers, regardless of their reputation.
Anyone for a Martin Logan? And the price! Quad was always expensive
kit. I know personally how difficult it is to make ESL speakers
because I once wasted 3 months trying to make a kit slapped shoddily
together by a Pom who'd emigrated to Perth. I could not find anyone
else who'd succeeded. Nobody understands Baxandal or Walker with
regard to ESL. They must if they really want to make a good ESL. But
Walker was able to mass produce ESL. He does get 10 out of ten for
perseverence! So he should have because he tried long enough and got
in before most others. I doubt anyone could replicate his success with
ESL now.

Today I have some B&O active 6000 series speakers here which cost a
pretty penny indeed and they have failed so miserably, speakers fallen
apart, amplifier fried, no proper protection. Bloody awful. Yet some
people love everything B&O make, but I can't because I have had to
service it. I don't like Bose systems either. There has always been
much audio visual gear which lacks true classic appeal, has terrible
quality, but sells for a small fortune. I see this as failure, not
success, and unfortunately with much of this stuff there is very
little in any of it which fertilises any mind anywhere.
if someone were to tell me the guy who invented B&O was a genious, and
that I should respect all he's done for it hath nothing bad about it,
then my reply would be polite, but obey I could not.

And while I'm at it, Phil says about Walker, "He also chose paper in
oil filter caps in preference to electrolytics to give the amp a long
life."

But fact is that in Quad-II, the grey boxed 16uF + 16uF caps are
labelled "electrolytic". Phil should get his facts straight. Walker
used electros all over his range of tube gear. He may have tried to
use the best parts he could find but the Hunts capacitors and carbon
composition resistors are garbage. No shame for Walker, but at that
time human kind had a long way to go to make R&C more reliable for
long amp life. The Poms built things like Spitfires which took
enormous skills and pilot's life depended on quality. But after WW2,
the average person got precious little Spitfire quality in anything he
bought. I can think of an exception - The Vincent Rapide.
Lord knows how many died enjoying the charms of a Vincent at speed.
Now there was something full of ideas which could be developed
further.

I'll do things here anyway I see fit, my way.

[John Byrns]

In article ,
Patrick Turner wrote:

Never for a minute did I ever expect to get any support on my anti-
sacred cow stance. From my greatest critics such as Phil I see almost
no creativity at all with regard to amplifier design.

What does Phil's creativity with regard to amplifier design, or the lack
thereof, have to do with whether or not the QUAD II was well designed for its
day?

OK, now I understand, this is not about shortcomings in the design of the QUAD
II, it is all about bashing what you call a "sacred cow", that seems like a
counter productive enterprise to me!

I am not criticizing your design abilities, at least in the realm of high end
cost is no object amplifiers using modern components.

The design brief for an amplifier includes more than the performance parameters
that you focus on. A few other points in the design brief might include the
price point, packaging issues, reliability considerations, and others.

So far your major proposed improvement for the QUAD II, in the context of its
day, is to use a "Williamson front end in place of the Paraphase front end that
QUAD used. This scheme has several down sides, including a heater current draw
higher by 0.8 amps. Without some lab work it isn't clear to me that the
Williamson front end would even offer improved performance in the QUAD II.

With respect to your frequently leveled criticism of the QUAD II's common output
stage cathode resistor, perhaps it isn't the fatal flaw that you make it out to
be. One web site says "In fact the BBC liked the QUAD II because it could
operate safely with only one output valve fitted", this implies to me that the
amplifier doesn't melt down if an output tube fails.

If I were doing the QUAD II in the day, I would stick with the paraphase front
end, as I don't share your paraphase paranoia.

The only improvement I would make would be to improve the hum and noise spec.
which is 80 dB below 15 Watts, I would make that 80 dB below 1 Watt.

It isn't clear what is causing the poor noise spec., it could be the input stage
which seems unlikely, or it could be poor layout and shielding of the power
wiring carrying 50 Hz frequencies, which would require improvements in the
layout or shielding of the power wiring, this would minimally impact cost. Or
it could be inadequate filtering of the 100 Hz power supply ripple, which could
be solved by suitable increases in the size of the filter caps, this would have
some impact of the parts cost.

The lack of a 4 Ohm tap on the output transformer isn't an issue in the context
of the Hi-Fi speakers that were available in the day. If it had been an issue,
if the speakers then had lower impedances, then it would have been a simple
matter to provide for 4 & 8 Ohm configurations, rather than 8 & 15 Ohms, using
the same 6 secondary sections, call it a rev. B version of the transformer
wiring.

--
Regards,

John Byrns

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

[Phil Allison[_3_]]

"John Byrns"

The only improvement I would make would be to improve the hum and noise
spec.
which is 80 dB below 15 Watts, I would make that 80 dB below 1 Watt.

It isn't clear what is causing the poor noise spec.,

** On my one example ( sn 8734 ) residual noise is mostly 50 Hz hum -
shorting or opening the input has no effect, so I the source is probably
EF86s heaters.

Eliminating the hum with a HPF leaves only a soft hiss which, best I can
measure, is 90uV rms or about 102 dB below 15 watts. In any normal listening
situation, even with efficient speakers ( say 100dB/W/m ) a listener hears
silence.

BTW:

The THD of my Quad II measures 0.048 % at 10 watts and 0.19 % at 15 watts at
1kHz and 8 ohms.

The EF86s are of unknown brand and decades old, while the output tubes are a
pair of well used Sylvania 6L6GCs.



..... Phil

[Phil Allison[_3_]]

"John Byrns"

The only improvement I would make would be to improve the hum and noise
spec.
which is 80 dB below 15 Watts, I would make that 80 dB below 1 Watt.


** My example measures 155uV ( 20Hz to 20kHz) = 97dB below 15 watts. Most
of this is 50 Hz and some 150Hz injection from the mains transformer -
which is larger than the original.

The multipin connector has been replaced with an 6.3mm jack, the Bulgin AC
inlet with an IEC and new resistors and film caps were fitted 30 years ago.
The original, loomed wiring is unchanged.

The -80dB figure is a furphy related to active supply wiring in close
proximity to a 1Mohm input.

It would still be inaudible in practice.


.... Phil

[Patrick Turner]

On Jun 11, 10:10*am, John Byrns wrote:
In article ,
*Patrick Turner wrote:

Never for a minute did I ever expect to get any support on my anti-
sacred cow stance. From my greatest critics such as Phil I see almost
no creativity at all with regard to amplifier design.

What does Phil's creativity with regard to amplifier design, or the lack
thereof, have to do with whether or not the QUAD II was well designed for its
day?

He's always advising people about all sorts of things and he loves
bashing them to death with words if they make a mistake yet he'd never
dare to give us a friendly discussable answer to your question about
what he might have done if I was in charge at Quad in 1951. He has no
website, and his efforts and maufacturing and selling amplifiers
amount to an invisible quantity afaik.

OK, now I understand, this is not about shortcomings in the design of the QUAD
II, it is all about bashing what you call a "sacred cow", that seems like a
counter productive enterprise to me!

In Oz, and unlike India, there are no sacred cows wandering the
streets which everyone must allow to wander because they are sacred.
If there were, I'd have to be nice to the cows if that was what
society expected of me. I'd never be not nice, and never bash them.
But there are plenty of humans and their inventions which have sacred
status amoung the thousands of members in the Cult Of Old Bwittish
Junke, which started in about 1930. They'd like us to all be driving
Daimlers without mods as they were in 1935, and if not, then riding
Norton 500cc singles. Maybe an AJS 7R or a Vincent. And listening to
mint condition Quads.
I'm not sure they would be listeing to the music though; we hear lots
of talk about amps and nothing about music. Pity help the man who
turned up to audio gathering on a Norton with Harley Sportster engine
and with a Quad fitted with a Dynaco ST70 front end.

Sacred cows in the form of an amplifier cannot feel pain and bashing
is permitted. Democracy hinges upon stern critiscisms. Many infernally
irritating men need a good bash whenever you see one, he's just been
up to no good, is in the middle of doing no good, or is plotting some
future no good. I wouldn't bash Walker, ever, but that doesn't mean I
cannot have a go at his products.

I'f I was a motoring enthusiast, I could have been asked what I might
have done differently if I'd been put back to 1920 in the Ford
Company. Sure, the Model A could have been a whole lot better. And who
would have paid for it? Recently there was a local gathering of a
dozen early Rolls Royces in a park here. Wonderful old motor cars, and
they ran silently and didn't smoke or leak oil. And it helped if you
were a millionaire if you wanted one. It sure pulled the chicks. Get
any chick you wanted any time.

I have no problems with identifying shortcomings of any darn thing
then seeing if some modern renovations can improve matters. Say you
buy an old castle. OK, its nice to install decent heating and flushing
toilet and a shower, because once you get the shiela back to the
castle after the party in the Rolls, ya don't wanna be carting damp
firewood to try to get her wamed up a bit for the important part of
the evenin'. So castles are fine things to modify. We could always
wonder how they could have been built to be a bit more user friendly
back when they were built in 1540 when blokes had very different ideas
about life, war, and shielas, and when there was a whole lot more
firewood and servants.


I am not criticizing your design abilities, at least in the realm of high end
cost is no object amplifiers using modern components.

But I'm not sure I'm hi-end. Most of my gear lacks the pretty finishes
and styling which characterises hi-end, while much high end is rather
poor when you examine under the bonnet. And cost is ALWAYS on my mind
whenever I build something. Usually I get paid very little for hand
crafted or re-engineered gear, and I just cannot buy some exotic core
materials and silver winding wire and caps worth $300 each unless
someone insist that I do so, with a barrow of bucks to pay for it.

The design brief for an amplifier includes more than the performance parameters
that you focus on. *A few other points in the design brief might include the
price point, packaging issues, reliability considerations, and others.

Indeed. I don't worry about price too much. I can only make for those
willing to pay more for a one of a kind amp set. A one man band can
compete with a mass production team.

So far your major proposed improvement for the QUAD II, in the context of its
day, is to use a "Williamson front end in place of the Paraphase front end that
QUAD used. *This scheme has several down sides, including a heater current draw
higher by 0.8 amps. *Without some lab work it isn't clear to me that the
Williamson front end would even offer improved performance in the QUAD II..

Be the naysayer if you wish. If you cannot see how a Williamson front
end is better than EF86 as done by Quad then you may be blind. I
suggest you carry out the necessary measurements. Quad-II PT could
have easily been made to cope with the increased heater current. I
have found that running KT88 instead of KT66 works fine even in Oz
with our hot summers, without any mods to PT.


With respect to your frequently leveled criticism of the QUAD II's common output
stage cathode resistor, perhaps it isn't the fatal flaw that you make it out to
be. *One web site says "In fact the BBC liked the QUAD II because it could
operate safely with only one output valve fitted", this implies to me that the
amplifier doesn't melt down if an output tube fails.

Hmm, that'd mean the apprentices at the BBC could sneak around
stealing on KT66 for their DIY home amps and they'd never be found
out.

Unfortunately, I have found many Quad-II amps with wildly different ia
in each KT66 which causes huge increase in IMD. The Rk = 180 ohms, and
if you pull one tube out, you have half the correct Rk for bias so
that tube will run way too hot. Left like that the OPT will cook to
death. I've had to repair amps where arcing ESL speakers have caused
serious overheating in the PT. The fuse doesn't blow, and only the
smell and distortion makes the owner realise the kids have got the
system turned up too loud. **** happens, and when it does amps should
turn off politely without heat stressing any parts. Now the Quad-II
Forty has individual R&C bias networks and it works so much better
than having a single Rk, ok in theory, ****in awful in practice, and
something that shortens tube life and amp life. Leak could afford the
extra 600 ohms and a 47uF, why couldn't Quad in 1950? ****in misers!

If I were doing the QUAD II in the day, I would stick with the paraphase front
end, as I don't share your paraphase paranoia.

You are welcome. Do all you wish your way. Maybe you could try a
Dynaco front end, only one 9 pin socket needed. But I wouldn't.


The only improvement I would make would be to improve the hum and noise spec.
which is 80 dB below 15 Watts, I would make that 80 dB below 1 Watt.

Quad-II has a frightful PSU, OK for where the amp is in class A, and
the speaker is 16 ohms and has sensitivity of 93dB/W/M at 100Hz, and
even more sensitivity at 1kHz. But they are hopeless for modern
conditions where you have a 4 ohm speaker rated for 87dB/W/M. My
website shows what to do about the PSU and other shortcomings, and
then they become passably usable amps even with the moden speakers and
heavy class AB action with a small % of pure class A.


It isn't clear what is causing the poor noise spec., it could be the input stage
which seems unlikely, or it could be poor layout and shielding of the power
wiring carrying 50 Hz frequencies, which would require improvements in the
layout or shielding of the power wiring, this would minimally impact cost.. *Or
it could be inadequate filtering of the 100 Hz power supply ripple, which could
be solved by suitable increases in the size of the filter caps, this would have
some impact of the parts cost.

I've never had hum problems in Quad-II once I've given the amps the
once over as spelled out at my website.

But in 1952, electro caps were much larger size per uF value. The
16+16 boxed caps used by Quad were quite good for that time. I have
many I have removed; most have probably survived a few bias failure
events.
Becasue the Quad chassis is so small there was no room for any more C
than PW was prepared to give anyone. The CMRR of the OP stage is very
good while each KT66 draws equal Idc and thus has equal Ra so that the
22vrms of ripple voltage at the CT is the same at both anodes. If the
Ra varies because of Idc variations there is a ripple signal across
the OPT anode coil and you get hum. I like 470uF at the CT, and such a
cap in 2011 is maybe 50 times cheaper in terms of week's wages than in
1952, and it has the same volume as 1/2 the box caps, and has 29 times
the C value. See my website for more about what could not be done in
1952.



The lack of a 4 Ohm tap on the output transformer isn't an issue in the context
of the Hi-Fi speakers that were available in the day. *If it had been an issue,
if the speakers then had lower impedances, then it would have been a simple
matter to provide for 4 & 8 Ohm configurations, rather than 8 & 15 Ohms, using
the same 6 secondary sections, call it a rev. B version of the transformer
wiring.

I'm not sure your solution is that simple, but the lack of an
efficient 4 ohm connection was a bad short coming.
Most US made amps had 4, 8 and 16 capability so why not Quad?

The existing sec windings on Quad-II have maximum seriesed turns for
16 ohms. They could have easily split the turns into two equal halves
for paralleling to get 4 ohms with low winding losses. This would
allow pure class A with 8 ohms connected, but pure class A into 4 ohms
was still impossible.

If you study all my pages devoted to OPT winding configurations you'll
see what was possible and what wasn't done.

Patrick Turner.

--
Regards,

John Byrns

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

[Patrick Turner]

On Jun 11, 12:35*pm, flipper wrote:
On Sat, 11 Jun 2011 11:42:22 +1000, "Phil Allison"
wrote:



"John Byrns"

The only improvement I would make would be to improve the hum and noise
spec.
which is 80 dB below 15 Watts, I would make that 80 dB below 1 Watt.

It isn't clear what is causing the poor noise spec.,

** On my one example ( sn 8734 ) residual noise is mostly 50 Hz hum -
shorting or opening the input has no effect, so I the source is probably
EF86s heaters.

Interesting because, according to Mullard, with the heater supply
center tap to ground hum through there should be less than from a
'poor' (leaky) socket.

Could socket aging be a factor? Or contamination?

No DC heater supply!

Patrick Turner.

[Patrick Turner]

On Jun 11, 11:42*am, "Phil Allison" wrote:
"John Byrns"



The only improvement I would make would be to improve the hum and noise
spec.
which is 80 dB below 15 Watts, I would make that 80 dB below 1 Watt.

It isn't clear what is causing the poor noise spec.,

** On my one example ( sn 8734 ) residual noise is mostly 50 Hz hum -
shorting or opening the input has no effect, so I the source is probably
EF86s heaters.

Eliminating the hum with a HPF leaves only a soft hiss which, best I can
measure, is 90uV rms or about 102 dB below 15 watts. In any normal listening
situation, even with efficient speakers ( say 100dB/W/m ) a listener hears
silence.

BTW:

The THD of my Quad II measures 0.048 % at 10 watts and 0.19 % at 15 watts at
1kHz and 8 ohms.

The EF86s are of unknown brand and decades old, while the output tubes are a
pair of well used Sylvania 6L6GCs.

.... *Phil

You are getting about the right measurements which are routine for the
amount of NFB and tubes used.

If you strap 8 ohms and use insensitive speakers of 4 ohms, Quad-II is
not so hot. Great for things like Dual concentric 15" Tannoy drivers,
16 ohms, 96dB efficient from 1960s in 150Litre ported boxes. Also OK
for ESL57 which have high Z at LF thus not generating much IMD at
higher F.
Most ppl just have modern insensitive speakers requiring class AB
action.

Patrick Turner.