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Old 13th December 2008, 12:37 PM   #1
Jaap is offline Jaap  Netherlands
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Default how to optimize this pentode PP (PP1 clone with S11E12)

I tried a pentode version of the PP1 amp with local (partial) feedback and a regulated screen supply.

I first used 100K between the plates of the 6H23 (= ecc88) and the EL34 or in my case the S11E12 (tried both). This sounded as too much feedback if you know what I mean (dead sound). After that I placed a 330K in series with the 100K but now the sound is too boomy (if that is a correct English word), I mean too much bass (unk, unk) which is tiresome after a while.

I suppose I have to choose a resistor in between 100K and 430K but what is optimal ? Another possibility is connecting the nodes between the 100K and 430K (or other values) with a resistor of 22K or whatever value is best. This is the solution "a la Baby Huey".
Or perhaps something else can be done ? I hesitated with global feedback till now.
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Old 13th December 2008, 12:41 PM   #2
Jaap is offline Jaap  Netherlands
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Default this is the PSU

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Old 13th December 2008, 12:48 PM   #3
SY is offline SY  United States
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We've had some discussions recently about using the secondary to provide feedback to the output tube cathodes. If it's centertapped (i.e., there's 16, 8, 4, and 0 taps), I'd think about going that route.
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Old 13th December 2008, 01:12 PM   #4
bigwill is offline bigwill  United Kingdom
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How about shunt feedback a la RH84 / RH807

Edit: Oh wait that's what you have Misread the schematic and thought I saw the feedback coming from the secondary
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