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Patrick Turner Patrick Turner is offline
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Default Dynaco MkIV monobloc re-engineering

I have very nearly finished re-engineering a pair of Dynaco MkIV monos.
I've replaced PT for 240V mains, and used completely new schematic with 2 x 6CG7 and 2 x KT88 output tubes, with emphasis on classA1 and fidelity rather than high power.
See my new page at http://www.turneraudio.com.au/Dynaco-mkIV-reformed.html

I have also edited an old page bout Dynaco ST70. This page did have my hand drawn schematic for what I did in 1999, and what a terrible mess that schematic was!

That schematic is still there, but a whole lot of new info is there now.

The ST70 can be taught to sing extremely well, using side cutters, hot soldering iron, and other implements of torture. It can also be taught to never smoke, by application of a minor amount of Squalid Steight devices.
See the revised page on ST70 at http://www.turneraudio.com.au/dynacost70mods.htm
Patrick Turner.
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Default Dynaco MkIV monobloc re-engineering


"Patrick Turner"

I have very nearly finished re-engineering a pair of Dynaco MkIV monos.


** Question for Pat.


The Dynaco Mk IV uses two EL34s in UL mode with a 470V supply - OK.

The published data for that UL of operation includes THD curves that barely
exceed 1% below clipping - with NO feedback applied .

However, Dynaco claim virtually the same THD figures, with circa 20dB of
feedback applied ??

Is the 7199's pentode gain stage mainly responsible for this anomaly ??

For comparison, the Quad II use two, low cost, EF86 pentodes in
differential mode to provide gain and phase inversion. The output stage uses
local (cathode) feedback, plus overall feedback but is otherwise
conventional PP with KT66s or 6L6GCs performing equally.

The Quad II achieves 0.1% THD at rated power and 0.05% THD at circa 10 watts
or less.



..... Phil




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Default Dynaco MkIV monobloc re-engineering

I mentioned that ........

I have very nearly finished re-engineering a pair of Dynaco MkIV monos.


** Question for Pat.


The Dynaco Mk IV uses two EL34s in UL mode with a 470V supply - OK.

The published data for that UL of operation includes THD curves that barely
exceed 1% below clipping - with NO feedback applied .

Well, a number of things affect published data which we always must question about conditions for the test unless fully stated. The only time anyone might achieve 1% THD at near full Po with any UL% taps between pure pentode/tetrode or triode will be with PURE class A1, and usually with only one load value, and with matched OP tubes and a distortionless driver amp.

In nearly every brandname PP amp I have tested, class AB operation is always used to boost the Po ability to get better amp sales. The most "honest test" is done using the rated load connected to the labelled output ohms, so with say 8r0 connected to an outlet labeled "8r0".

Consider MkIV Dynaco. I recall B+ = Ea = +440Vdc. If the EL34 have Pda = 22Watts each, then Ia = 50mA, and if Ig2 = 6mA, then total Pda + Pg2 = 24.6Watts, which I consider a bit too high. But anyway, Total Pda = 2 x 440V x 0.05A = 44Watts, and Class A anode efficiency = 45% so max Class A1 Po = 19.8Watts.

The approximate RLa-a for pure class A1 = 15,840 ohms. The MkIV has OPT with nominal RLa-a = 4.300 ohms for 4r, 8r, 16r secs, and let us say we choose to use the 4r outlet, where ZR = 1,075:1. The load we would need to use to get RLa-a of 15k8 = 15,840 / 1075 = 14r6, ie, more than 3 times the labeled outlet value. Load line analysis will back up everything I say here. Now with 14r6 at 4r0 outlet, perhaps THD might be under 2% at 19.8Watts, with no GNFB.
But with 4r load at 4r0 outlet, the pair of EL34 struggle to have THD under 4%
at clipping, and at whatever rather high Po that might be. Using lower B+ and KT88 lessens the THD for same or slightly higher Po.

However, Dynaco claim virtually the same THD figures, with circa 20dB of
feedback applied ??

I searched around for data on MkIV and I didn't find any info saying THD was the same with or without NFB. Perhaps you found a more informative source of info. The info I have talks about IMD, not THD, and there was nothing surprising, but then also no exact statements about how tests were made.

Is the 7199's pentode gain stage mainly responsible for this anomaly ??

The pentode section of 7199 has to make Va slightly exceeding Vg of one EL34.
This is about 26Vrms at clipping, and THD will definately be over 1%.
And many H are present and its adds to THD of class AB EL34, so expect 3% or more without GNFB. The 20dB NFB reduces this to about 0.3%, and this is typical real world behaviour.

For comparison, the Quad II use two, low cost, EF86 pentodes in
differential mode to provide gain and phase inversion. The output stage uses
local (cathode) feedback, plus overall feedback but is otherwise
conventional PP with KT66s or 6L6GCs performing equally.

The EF86 of Quad-II are not quite in pure differential mode. In fact, the pair of EF86 are set up as a paraphase pair where output from Va at one EF86 is resistored down to feed the grid of other EF86, and common cathode R is bootstrapped by the GNFB resistance network. Its all so very clever, this arrangement, and hardly anyone fully understands the several things going on simultaneously, to achieve the use just two little piddly EF86 to drive a pair of KT66. The Quad-II set up feeds the distortion of one EF86 to the other where the odd order H add while some even order cancel. The Quad-II driver amp has more THD than if twin triodes similar to Williamson, or Leak, or anything at my website.
In one pair of Quad-II I re-engineered, I set up the EF86 as a true differential amp. I set up a -400Vdc supply from which I had a large value R from -400Vdc to commoned cathodes. The GNFB is fed only to the grid of secons EF86, and there is no paraphase connection. This halved the THD. But in 1950, the idea of -400V or even -40V and a CCS to cathodes was just not on - too complex, too pure, too good, and too damned expensive while the rest of the world's amp industry colluded to make the lowest common denominator product for maximal shareholder returns.

The Quad II achieves 0.1% THD at rated power and 0.05% THD at circa 10 watts
or less.

Well all that depends on load conditions, and perfect tube matching, and almost no Quad-II amps I've tested achieve these wonderful figures you quote.
Usually, with perfect test conditions, the tube matching makes sure the 2H current production is so close that whatever difference there is remains less than the amount of 3H which is always the major H in what you see in PP amps
while still working in class A1. When the action becomes class AB, then you get far more than 1% and an an increasing number of odd and even H and PSU noise.

I very much liked Quad's idea of cathode feedback windings on the OPT. I recall making my first 8585 amp and I originally had 4 x GE6550A in each channel with Ea = 400Vdc, Ia at 55mA, and I saw 50Watts at 0.7% THD without GNFB but with partial UL connection of screens and with 12.5% CFB
I found I could raise Ea to 480Vdc, and used a fixed Eg2 like Quad, but lower Vdc than Ea, and still get excellent THD results which were consistently better than triode, or any % of UL.

Patrick Turner.

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Default Dynaco MkIV monobloc re-engineering


"Patrick Turner"


I have very nearly finished re-engineering a pair of Dynaco MkIV monos.


** Question for Pat.

The Dynaco Mk IV uses two EL34s in UL mode with a 470V supply - OK.

The published data for that UL of operation includes THD curves that barely
exceed 1% below clipping - with NO feedback applied .

Well, a number of things affect published data which we always
must question about conditions for the test unless fully stated.


** See:

http://www.r-type.org/pdfs/el34.pdf

37W = 1.3% THD class AB ( just )
20W = 0.8% THD class A

Schem and curves are shown half way down the same page.
-------------------------------------------------------------------

However, Dynaco claim virtually the same THD figures, with circa 20dB of
feedback applied ??

I searched around for data on MkIV and I didn't find
any info saying THD was the same with or without NFB.



** Of course you did not, cos that is NOT what my post says !!!


Is the 7199's pentode gain stage mainly responsible for this anomaly ??

For comparison, the Quad II use two, low cost, EF86 pentodes in
differential mode to provide gain and phase inversion. The output stage uses
local (cathode) feedback, plus overall feedback but is otherwise
conventional PP with KT66s or 6L6GCs performing equally.

The Quad II achieves 0.1% THD at rated power and 0.05% THD at circa 10 watts
or less.

Well all that depends on load conditions, and perfect tube matching, and
almost no Quad-II amps I've tested achieve these wonderful figures you
quote.

** Really??

IME they all do.

My example tests 0.03% at 10W with rather worn Sylvania 6L6GCs and very old
EL84s.



..... Phil




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Default Dynaco MkIV monobloc re-engineering

The published data for that UL of operation includes THD curves that barely
exceed 1% below clipping - with NO feedback applied .

Well, a number of things affect published data which we always
must question about conditions for the test unless fully stated.


** See:

http://www.r-type.org/pdfs/el34.pdf

37W = 1.3% THD class AB ( just )
20W = 0.8% THD class A

Schem and curves are shown half way down the same page.
-------------------------------------------------------------------

However, Dynaco claim virtually the same THD figures, with circa 20dB of
feedback applied ??

I searched around for data on MkIV and I didn't find
any info saying THD was the same with or without NFB.



** Of course you did not, cos that is NOT what my post says !!!

I am aware that your reference was not to what Dynaco did / didn't say, but referred to Mullard data or equal or same from 1954.

Is the 7199's pentode gain stage mainly responsible for this anomaly ??

One fact is that Dynaco has 7199 pentode in SE mode, so a mix of odd+even H are produced. The absence of a balanced LTP drive amp in MkIV means pentode even H are not reduced by the balanced action of an LTP. At least some reduction of 2H in in EF86 in Quad-II is achieved.

For comparison, the Quad II use two, low cost, EF86 pentodes in
differential mode to provide gain and phase inversion. The output stage uses
local (cathode) feedback, plus overall feedback but is otherwise
conventional PP with KT66s or 6L6GCs performing equally.

Agreed, except that now, who cares about EF86 being cheap?

The Quad II achieves 0.1% THD at rated power and 0.05% THD at circa 10 watts
or less.

Well all that depends on load conditions, and perfect tube matching, and
almost no Quad-II amps I've tested achieve these wonderful figures you
quote.

** Really??

IME they all do.

I think not all,because tube properties affect THD. In any typical Quad-II, swapping positions of KT66 can make a big difference to THD because of 2H cancelling, and also when changing positions of EF86. Some working serviceable Quad-II I have tested have THD way above the Data Quad crow about. Peter Walker knew all about the limitations of his amps and the effects of aging. But 99% of Quad-II users would not hear any indication whatever that THD at say 3Watts was 10 times higher than the THD curves for Quad-II might indicate. Most ppl listened at less than average of 1Watt, so discussions of THD become academic value for most. And by listeners I include maybe hundreds of professional guys in recording studios monitoring what they did between 1950s and 1970s, by which time the tube gear was largely banished, replaced by SS with lower THD but which may have sounded no better, if we are to listen to what some audio enthusiasts say.

My example tests 0.03% at 10W with rather worn Sylvania 6L6GCs and very old
EL84s.

?? I think you mean "worn Sylvania 6L6GCs and very old EF86"

I have a UL PP amp in my shed which has the first OPT I ever wound in 1994 and it had ancient worn Sylvania 6CA7 in PP with 50% UL taps but has 12AT7 paralleled for input, 6CG7 driver in LTP. The B+ is a regulated +400V and and I have fixed bias, so no mis-biasing because of Ek rise during class AB which usually makes all AB amps display much higher THD than with fixed bias.
With 15dB GNFB I got 0.125% THD at 32 Watts, AB1, and THD was better than proportional to Vo, so that at 10W where Po was all class A1 I got about 0.06%,
and about what anyone could expect. If I put on 6dB more GNFB, THD would be half the above figures.
Over time the 6CA7 gave up, and began overheating when g1 bias failed to keep the Ia under control due to tube gas increasing. So I changed to KT88 and amp gives over 50W max and very good THD figures. UL IS GOOD, no doubt about it, but well done CFB is better.

I share Quad's belief that the CFB from OPT very much linearizes all output pentodes and tetrodes, and works better than the lazier use of UL taps and because the CFB is applied around a linear external loop including the higher gm of grid 1, not just the slightly non linear action of g2 which has a low gm and cannot do much when the RLa-a goes low, as it surely does when designers don't provide outlets of OPT straps to allow a match to 4r0. Many ppl use 4r0 speakers with Quad-II strapped for the lowest recommended strapping for 8r0, and then the THD becomes quite high.

When I removed the OPT bell ends from Dynaco MkIV OPTs, I found enough sec windings to allow the sec turns to be changed to get 8k6 : 8r0 and 8k6 : 3r5 and because I've used KT88 and all triode drive amp, I can boast that the MkIV will outperform any Quad-II in all ways that can be measured.

During the re-engineering process of MkIV, I did consider using a choke with grounded CT and between KT88 cathodes and with cross coupling by elcaps from cathodes to OPT screen connections. It effectively doubles the RLa-a, without changing the sec windings. And in class AB, more than 1/2 the OPT primary is used. The MkIV has 33% UL taps, so CFB% would have been high but about 80Vrms needs to be applied to each output grid. But under the MkIV chassis there just wasn't room for extra L and C parts so I settled for a plain UL schematic similar to one channel of a 5050 amp you'll find at my website.

High CFB% yields very low output stage THD but then driver design has to be very good, because the total amount of GNFB + CFB should not exceed 20dB, so there is a point where increasing CFB and then lowering GNFB means that driver amp THD is not reduced by the lowered amount of GNFB. McIntosh take matters further with 50% CFB, and when loaded to give pure class A, they are remarkably linear.
I much like Olde Quads, but its so easy to make them better. I have a pair which soon will get full treatment. I have a pair of new OPTs I had specially wound by a Chinese guy in Sydney who really knows what he's doing. Old Quad-II OPTs will go into another amp to replace far worse OPTs I had scrounged from somewhere. The tube rectifier will go and the screen choke, and that's where driver triodes will go because new OPT occupies where old one was plus where EF86 were placed.

The arguments which have been most relevant to my ears for last 20 years have been about what sounds better, and generally, I got better reports for my gear I'd made if I used better techniques than found in original Quad-II.

In my SE32 amp, I have a single 13E1, it uses some g2 FB, and 33% CFB, and I get 32W and very low THD for an SE amp. Same goes for SE35, with 4 x EL34..

It ain't what you got that counts, its how ya use it.

All past amplifier techniques may be questioned, lest we have to put up with mediocre crap which could not perform optimally in 1955 because they didn't have the diodes and caps and low prices in real terms that we have now.

Patrick Turner.


..... Phil


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Default Dynaco MkIV monobloc re-engineering


"Patrick Turner"

The published data for that UL of operation includes THD curves that barely
exceed 1% below clipping - with NO feedback applied .

Well, a number of things affect published data which we always
must question about conditions for the test unless fully stated.


** See:

http://www.r-type.org/pdfs/el34.pdf

37W = 1.3% THD class AB ( just )
20W = 0.8% THD class A

Schem and curves are shown half way down the same page.
-------------------------------------------------------------------

However, Dynaco claim virtually the same THD figures, with circa 20dB of
feedback applied ??

I searched around for data on MkIV and I didn't find
any info saying THD was the same with or without NFB.



** Of course you did not, cos that is NOT what my post says !!!

I am aware that your reference was not to what Dynaco did / didn't say,

** You are now.

Is the 7199's pentode gain stage mainly responsible for this anomaly ??

For comparison, the Quad II use two, low cost, EF86 pentodes in
differential mode to provide gain and phase inversion. The output stage uses
local (cathode) feedback, plus overall feedback but is otherwise
conventional PP with KT66s or 6L6GCs performing equally.

Agreed, except that now, who cares about EF86 being cheap?

** Massive red herring.


The Quad II achieves 0.1% THD at rated power and 0.05% THD at circa 10 watts
or less.

Well all that depends on load conditions, and perfect tube matching, and
almost no Quad-II amps I've tested achieve these wonderful figures you
quote.

** Really??

IME they all do.

My example tests 0.03% at 10W with rather worn Sylvania 6L6GCs and very old
EF86s.

It has no circuit mods at all, other than using a diode rectifier.

Cos it does not need any.



.... Phil



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"Phil Allison"
"Patrick Turner"

The published data for that UL of operation includes THD curves that
barely
exceed 1% below clipping - with NO feedback applied .

Well, a number of things affect published data which we always
must question about conditions for the test unless fully stated.


** See:

http://www.r-type.org/pdfs/el34.pdf

37W = 1.3% THD class AB ( just )
20W = 0.8% THD class A

Schem and curves are shown half way down the same page.
-------------------------------------------------------------------


** More info:

In order to find the " open loop " THD of a Quad II output stage, I
removed the two EF86s and connected an output tranny primary to
the + supply and both plate pins.

The secondary was then driven by my bench oscillator, which has
very low THD - circa 0.002%.

This gave 52Vrms from grid to grid on the output valves - enough to
drive the stage to 10 W at 8 ohms and 1kHz.

Results: THD = 0.76%, DF = 1.

Also tried were Electro-Harmonix and GE 6L6GCs with closely similar
results, the EHs producing 0.8% and the GEs about 0.7%.

With EF86s restored to their sockets and the OP tranny removed, THD
dropped to 0.036% ( 10W, 8ohms) and DF improved to a respectable 10.

My conclusion is that the two EF86s reduce the THD of the output stage in
line with the level of NFB being used ( ie 26dB ) while adding virtually
*NONE* of their own.

Nice.


..... Phil




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Phil says more about Quad-II.....

** More info:

In order to find the " open loop " THD of a Quad II output stage, I
removed the two EF86s and connected an output tranny primary to
the + supply and both plate pins.

The secondary was then driven by my bench oscillator, which has
very low THD - circa 0.002%.

This gave 52Vrms from grid to grid on the output valves - enough to
drive the stage to 10 W at 8 ohms and 1kHz.

Results: THD = 0.76%, DF = 1.

***This is all to be expected because with Quad-II OPT strapped for 8r0,
and load = 8r0, the RLa-a = about 4k0, so each KT66 sees a class A load of 2k0.
Above 10W, Po is class AB1 to a maximum of about 22Watts. If a 16r0 load is used at 8r0 strapping, then each KT66 sees RLa = 4k0 and RLa-a = 8k0 and Po = about 20Watts, and is all class A1 if Iadc = 70mA. Perhaps if you test with 16r0 instead of 8r0 the THD would fall even lower than you say it is.

Now if we ignore winding losses, KT66, the 4k0 load Voltage across anode turns and cathode turns = 200Vrms, and Iac = 50mArms = 70mApk. And if the tubes have Iadc at idle = 70mAdc, then the amp is in pure class A. While this is the case, the 10% CFB windings make the two KT66 tetrodes behave almost identically to when they are strapped in triode mode and have no CFB windings. BUT, the CFB connection with fixed Eg2 allows the Va swing to reach down to virtually the same Ea min to when KT66 are used in pure tetrode mode. Hence more maximum Po is available beyond the first 10 Watts.

Also tried were Electro-Harmonix and GE 6L6GCs with closely similar
results, the EHs producing 0.8% and the GEs about 0.7%.

***Typical expected results.

OPT has ZR 4,000 : 8 = 500:1 so if you measured DF = 1, the Rout = 8r0, so at primary the Ra-a must be 500 x 8 = 4,000 ohms and this is equal to RLa-a. Indeed DF without GNFB is 1. It means effective Ra of each KT66 / 6L6GC is vastly reduced from 33k approx to 2k0. Not quite as low as triode connected KT66, but
is lower than plain old UL. Mind you, when OPT winding losses are included in considerations the Rout comprises Rw, and then you'd find the effective Ra is closer to the 1k6 of triodes.

With EF86s restored to their sockets and the OP tranny removed, THD
dropped to 0.036% ( 10W, 8ohms) and DF improved to a respectable 10.

***So reduction of THD you measured with input stage and its GNFB loop is from 0.7% to 0.036% which indicates D% red factor = 1/19.4 = - 25.6dB.


My conclusion is that the two EF86s reduce the THD of the output stage in
line with the level of NFB being used ( ie 26dB ) while adding virtually
*NONE* of their own.

***OK, I agree with your 26dB. I'd have to check my notebooks to see if I ever measured 0.036% at 10Watts, but I cannot now recall ever seeing THD that low.

The THD will probably be, or SHOULD mainly be 3H because 2H and other even H should be cancelled by balance action. If the phase of 3H produced by EF86 is opposite that produced by KT66, then 3H cancelling is happening. Most class A output stages make 3H which shows up as slight flattening of wave peaks. But pentodes can produce more peaky waves. Pentodes do odd things, and the 2H and 3H produced by a single pentode change in amplitude with different RLa, and 2H can be similar to a triode for low RLa and as RLa becomes higher, 2H declines to zero then rises after a certain RLa value. But the phase of 2H above the null is opposite to below, and I suspect when a balanced pair are used the outcome gives cancelled 2H but 3H with peaks in phase with H1 signal phase.

Have you worked out how much applied GNFB occurs in Quad-II ? I don't recall ever measuring 26dB.

If Va to Vk = 100Vrms for each KT66, 6CA7, whatever, then each Va = 90Vrms+ and at cathode Vk = 10Vrms-, and if Vg1 = 26Vrms, then Vg1 to Vk = 16Vrms, and one might say there is CFB gain reduction from 6.25 to 3.85, so about 3dB NFB, but its more because of the UL screen FB between g2 and k. Its a bit tricky to quantify FB because there are 2 loops involved. Its simpler if each KT66 g2 is bypassed to k with its own cap, then action becomes pure beam tetrode with 10% CFB, and the Gain red is more. But the fixed Eg2 probably gives some reduction of odd H that is more than with g2 bypassed to k. Of course, g2 on one KT66 can be bypassed to k on opposite KT66, so tubes are working with 20% UL and with CFB.

So, say CFB including the 10% UL from fixed Eg2 gives a total of 6dB CFB, then total FB used is 26 + 6 = 32dB, which I do not believe exists until indicated otherwise by some scholar here. Total FB is more like 20dB I recall; I am not sure, been awhile since I did the numbers.

I just dug up another schematic of mine - a 2010 reformed Quad-II with 6BX6 / EF80 used as a pure diff pair, and KT88, and dynamic bias stabilization which makes a 35 Watts max, and very good first 10 Watts. So Quad-II can be made to perform as well as Quad-II-Forties.
Patrick Turner.

Nice.


..... Phil

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"Patrick Turneroid"


** More info:

In order to find the " open loop " THD of a Quad II output stage, I
removed the two EF86s and connected an output tranny primary to
the + supply and both plate pins.

The secondary was then driven by my bench oscillator, which has
very low THD - circa 0.002%.

This gave 52Vrms from grid to grid on the output valves - enough to
drive the stage to 10 W at 8 ohms and 1kHz.

Results: THD = 0.76%, DF = 1.

***This is all to be expected


** You bull****ting asshole !!

You had no idea what the THD figure was *open loop* !!!.


Also tried were Electro-Harmonix and GE 6L6GCs with closely similar
results, the EHs producing 0.8% and the GEs about 0.7%.

***Typical expected results.


** You bull****ting ASSHOLE !!

You had no idea what the THD figures for those tubes really were.

I only mentioned them to show the THD result was easily repeatable.


With EF86s restored to their sockets and the OP tranny removed, THD
dropped to 0.036% ( 10W, 8ohms) and DF improved to a respectable 10.

My conclusion is that the two EF86s reduce the THD of the output stage in
line with the level of NFB being used ( ie 26dB ) while adding virtually
*NONE* of their own.

***OK, I agree with your 26dB. I'd have to check my notebooks to see if I
ever measured 0.036% at 10Watts, but I cannot now recall ever seeing THD
that low.

** That would be because you LOATHE the Quad II so much you cannot bring
yourself to put in the effort to restore one to original specs and SEE how
well it works.

**** off and die you vile freak.



..... Phil


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"Phil Allison"
In order to find the " open loop " THD of a Quad II output stage, I
removed the two EF86s and connected an output tranny primary to
the + supply and both plate pins.

The secondary was then driven by my bench oscillator, which has
very low THD - circa 0.002%.

This gave 52Vrms from grid to grid on the output valves - enough to
drive the stage to 10 W at 8 ohms and 1kHz.

Results: THD = 0.76%, DF = 1.


** Correction, the above THD figure is in error.

Magnetising current in the output tranny caused far more 3H than I had
hunched for the low level and 1kHz frequency I was using.

So I repeated the test with a 100W mosfet amp as a buffer between the
bench oscillator and the tranny - the THD from this set up was checked
at 0.04% at 52V rms.

The corrected figure is a staggering 0.18% THD.

I was so surprised at this result, I repeated the measurement in various
ways several more times.

Peter J. Walker sure knew what he was doing when he went with cathode
feedback for that output stage rather than UL or similar.


..... Phil





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Phil mentioned....


Peter J. Walker sure knew what he was doing when he went with cathode
feedback for that output stage rather than UL or similar.


..... Phil

He sure did know, there is no doubt. I am not 100% sure that you know exactly what all of his thinking was, and maybe nobody does because of concerns about being private for good reason. But he also had an ego, and wanted to be original, and profit by claiming superiority. Its OK, human nature.

In another post Phil calls me all sorts of names but does nothing to me.

I have meanwhile re-edited my page http://www.turneraudio.com.au/quad2powerampmods.htm

I measured the THD Vs Po for an original Quad-II in good condition and for open loop and for closed loop, AND I added the graph for Dynaco MkIV with similar class AB loading to make the comparison fair.
I also re-drew tie THD I got with KT90 used to replace KT66 in a reformed amp.

Whatever anyone wants to know about Quad-II is at my page, including a full description of the OPT which is wound extremely well. Except that it is too small, with winding resistances a bit too high. And Peter left out one extra
terminal to allow wasteless sec windings for 4r0 strapping. But upon consideration, and after drawing a graph for Po vs RL for the 3 possible OPT strappings, the performance when yellow speaker wire from output terminal is connected to Point Q is OK, even though its rarely mentioned anywhere.

However, winding resistance, ie, the resistance of copper wire is benign and Peter Walker knew nearly everyone did not need 20 Watts, so it does not matter that the tubes make 25Watts while putting out 21Watts to the load.

Patrick Turner.
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