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OTL Asylum OTL, Output Transformerless Amplifier User Group. |
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OTL Asylum OTL, Output Transformerless Amplifier User Group. |
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In Reply to: ADJUSTING BOTH SIDES OF A 6AS7 posted by AL on January 1, 2001 at 08:27:10:
I assume you're talking about the amplifier on the Svetlana site found at http://www.svetlana.com/docs/TechBulletins/appnoteNO.26.html.This circuit is very different from that used in our Atma-Sphere amps. The Svetlana site describes a single-ended output with the two halves of a 6AS7G in parallel. Our amplifiers's output stages are paralleled circlotrons, driven by differential cathode followers. They are run fixed bias. This is a very different topology than used in a single-ended amp. You could add the rheostat, like that used in the Svetlana amp, but you'd effectively add that same resistance in series with the output terminals on the amp. This would significantly effect the amplifier's power output and dampening factor. This approach simply would not do the job.
Let's assume you want individual bias adjustment for each output tube section. You'd need a separate 6SN7 driver stage for each pair of 6AS7 triodes in each phase. So, assuming the M-60, you've got 16 individual output triodes. This means you'd need to duplicate the V4 circuitry 8 times. You'd need 8 driver tubes per chassis! You'd need a much larger driver supply and filament supply to handle the extra load. You'd also find it difficult to drive all the extra output tube driver tubes with the existing cascode input stage. Add another intermediate buffer at a cost of two more 6SN7s.
So, I hate to be a party pooper, but the moral of the story is becoming clear. Get the output tubes reasonably matched and then sit down, shut up and enjoy the music!
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Follow Ups
- Re: ADJUSTING BOTH SIDES OF A 6AS7 - mark 16:11:28 01/01/01 (2)
- Re: ADJUSTING BOTH SIDES OF A 6AS7 - AL 13:19:43 01/02/01 (1)
- Re: ADJUSTING BOTH SIDES OF A 6AS7 - mark 14:09:06 01/02/01 (0)
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