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Old 4th September 2010, 08:32 PM   #1
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Default To Schade it , or not..

After drinking half a Ballantines bottle, I come out with this thing. Now, ten "ristretto" coffees after that, I start to suspect that there is something wrong about this plate to plate connection. Schade can wait?
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Old 4th September 2010, 11:03 PM   #2
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As long both AU6 stay in Class A, should be able to tolerate 6V6 in AB...
You got autotransformer coupling of NFB from plate of downside 6V6.
Even when topside 6v6 is temporarily class B'd out the picture.
I don't know this is Schade anymore, but still plate to plate feedback.

I'm a little more worried you got c1, c2, and maybe c5 together with
autotransformer in a feedback loop to control the downsize 6v6. One
corner has to be sufficiently lower than the rest to assure that loop
gain is down below unity before the next pole adds any more pshift.

Would R10 operate better bypassed? We want voltage linearity for
this triode strapped AU6 phase inverter, don't care current linearity.

Last edited by kenpeter; 4th September 2010 at 11:22 PM.
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Old 4th September 2010, 11:12 PM   #3
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Mmm... I wanted to have some O/P impedance reduction, but maybe is better this one. Of course, being a pure pentode output stage GNF is a must to do
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Last edited by Mosquito; 4th September 2010 at 11:16 PM.
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Old 4th September 2010, 11:27 PM   #4
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The plan was to keep R5 bigger than R7, and C1 smaller than C2
C5 instead, some 30 to 40uF lytic...
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Old 5th September 2010, 05:16 AM   #5
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Gnd 4 ohm tap and stand output cathodes on 0 and 16...
Though would then need fixed (negative) bias for grids.
See ARC ST-70-C3 for classic example.

Does top AU6 in unbypassed pentode mode make sense
without plate to plate NFB?

Last edited by kenpeter; 5th September 2010 at 05:33 AM.
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Old 5th September 2010, 08:28 AM   #6
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Yes probably in a nornal GNF scheme it is better to keep R9 bypassed, for a plenty of gain. (It is not pictured, but I want the amp to be an integrated, drived directly by the CDP out, if possible)
R10 unbypassed is part of the measures to have unity gain on the second AU6, a much lower voltage gain, G1 feeded trough a voltage divider, and a lower following grid resistor (R7)
Found the schematic You suggested (ARC ST-70-C3) I'll take a look on it.

Last edited by Mosquito; 5th September 2010 at 08:48 AM.
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Old 5th September 2010, 09:23 AM   #7
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Maybe for a correct use of Schade local FB it is necessary to build some kind of LTP or differential input stage keeping both AU6's in pentode mode?
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