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Old 13th July 2010, 10:44 AM   #1
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Default Class B Push-Pull

Greetings everyone,
With proper feedback, how bad will a class B push-pull sound?

Thanks,
Ray
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Old 13th July 2010, 04:42 PM   #2
kevinkr is offline kevinkr  United States
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It depends on how good you are at designing a solution for what happens in the cross-over region from one output tube to the other..

McIntosh made some pretty good sounding, but fairly complex class B/near class B amplifiers with very clever transformer design (unity coupled) to minimize the effect of cross-over distortion in their output stage.

Why anyone would necessarily want to/need to copy this approach today is a question I can't answer..

Need really high power go solid state..
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Old 13th July 2010, 07:43 PM   #3
SY is offline SY  United States
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Screen drive of high perveance tubes also seems to work very well at a cost of very high drive requirements. My last big amp ran near-Class-B and sounded fine. Tubelab has been making similar efforts recently and his are well worth exploring.

You might want to study the David Berning EA230 and EA2100/2101 designs.
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Old 13th July 2010, 08:10 PM   #4
banat is offline banat  Serbia
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Class B mean long live for output tubes too and high overall Amp eficiency. ,Mcintosh solved crossover class B switching with `Unity coupling`design of output stage&OPT but Electro Voice solved that with Circlotron output stage design very efectiv too.BTW ElectroVoice/Voima /Circlotron OPT(or autotransformer)is very simple to made.Good Luck to Everybody
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Old 13th July 2010, 08:29 PM   #5
bigwill is offline bigwill  United Kingdom
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Quote:
Originally Posted by SY View Post
Screen drive of high perveance tubes also seems to work very well at a cost of very high drive requirements. My last big amp ran near-Class-B and sounded fine. Tubelab has been making similar efforts recently and his are well worth exploring.

You might want to study the David Berning EA230 and EA2100/2101 designs.
Out of interest, how well does screen drive work with the usual suspects? (EL34, KT88 etc)
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Old 13th July 2010, 08:31 PM   #6
SY is offline SY  United States
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Not well in comparison. Take a look at the curves for (say) a 6JN6 at vg1 = 0 and vg2 the variable, then compare them to the same curves for (say) a 6L6.
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Old 13th July 2010, 09:54 PM   #7
kevinkr is offline kevinkr  United States
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Quote:
Originally Posted by banat View Post
Class B mean long live for output tubes too and high overall Amp eficiency. ,Mcintosh solved crossover class B switching with `Unity coupling`design of output stage&OPT but Electro Voice solved that with Circlotron output stage design very efectiv too.BTW ElectroVoice/Voima /Circlotron OPT(or autotransformer)is very simple to made.Good Luck to Everybody
Circlotrons are typically class A to some level of output and then AB the rest of the way to full output to the best of my recollection - there has to be some minimum current flowing in the loop at all times for reasonable linearity.
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Old 13th July 2010, 10:15 PM   #8
banat is offline banat  Serbia
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Circlotrons are typically class A to some level of output and then AB the rest of the way to full output to the best of my recollection - there has to be some minimum current flowing in the loop at all times for reasonable linearity.
Hi Kevin Kr. Class A/AB for some OTL Circlotron design is 100% truth but ElectroVoice Circlotron with OPT design is AB biased but much closer to B class biased(A100 model for example).You can found that EV Amp schematic on Net site -Circlotron History page-.One of advantages of Circlotron (OPT or autoformer) Amp design biased near to Class B is no switching transient and wide frequency range,this second is due wery simple OPT or autoformer,and long output tube live/high overall Amp eficiency(mentionet before)
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Old 13th July 2010, 10:26 PM   #9
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Autoformers are excellent output devices. I played with variac and found it very handy.
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Old 14th July 2010, 07:04 AM   #10
Yvesm is offline Yvesm  France
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. . .
but Electro Voice solved that with Circlotron output stage design very efectiv too.BTW ElectroVoice/Voima /Circlotron OPT(or autotransformer)is very simple to made.Good Luck to Everybody
Yes, but keep in mind that the two power supplies MUST float at ALL frequencies, not simply DC insulated.
This usually asks for a specially wound power transformator with very high leakage inductance between the two HV windings . . . no free beer !

Also consider Norman Crowhurst's approach with two independent OPT coupled by their secondary (for lo frequency) and the two caps "cross coupling" each anode to the opposite cathode for hi end.
http://www.dissident-audio.com/AutoI...0crowhurst.pdf

Yves.
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