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In Reply to: RE: FWIW the GRAAF GM 200 and the GM 20 are quite different. posted by Ralph on February 01, 2012 at 12:26:40
I briefly looked at the schematic that Luca provided, and I do believe I saw a separate supply for the front end of the GM20. But the output tubes shown on the GM20 schematic are unlabeled triodes, which I believe to have been 6C33Cs. Whereas the GM200 is using something else for outputs that appear to be pentodes. In a circlotron, which the GM20 is, could one run the front end off one or both of the output supplies, successfully? I would not have thought so.
Follow Ups:
Hi Lew !From my attached link you can download more accurate schematic of Graff GM 20 power Amp .
There is obviously that input differencial stage (6922 tube) is AC bootstraped to output Circlotron power bridge , formed around of two 6c33c-b power tube .
Input differencial stage (6922 tube) DC B+ feed is sourced from the same output power two floating B1/B2+ power supply .
Two separate DC bipolar supply sources is designed to be B+ source for two drivers EF184 tubes (+297V ), differencialy conected .
And - 250 V source is designed to be the B- supply for both differencial input and driver stage , and in the same time is source for negative B- Bias supply for output Circlotron power stage .
It is my personal opinion that model Graff GM200 is designed in simmilar way , more or less .
Best Regards !
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Enlightened Evolution-Astral Projection
Edits: 02/01/12
Yes, I see now that that separate supply at the bottom of the schematic is merely the bias supply for the grids of the output tubes. Interesting.
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Yes I agree with You !More time I spend analyzing this Graff GM20 OTL Circlotron circuit design I find him more and more that is very,very good designed !, and is designed in very elegant way to .
Think beacose that differencial Input gain stage is bootstrapped with Output Circlotron power stage the whole amp circuit is internally very dynamically coupled , and some specific resulting Amp sonic signature exist there for sure to .Best Regards !
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Enlightened Evolution-Astral Projection
Edits: 02/01/12
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