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Old 31st December 2009, 04:46 PM   #11
rdf is offline rdf  Canada
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For me, I would never use a plate choke unless I absolutely needed the swing- they're large, expensive, and subject to all sorts of unpleasant non-ideal behavior.
Especially with a high Rp tube. I recently tried 150H Hammonds on 6FY7 small triode sections (Rp ~ 30k) in a circuit with marginal B+, hoping for more plate voltage. Never made it off the bench, way too much distortion. No free lunch.
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Old 31st December 2009, 04:59 PM   #12
kevinkr is offline kevinkr  United States
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Use a good plate choke and a low rp triode like the 5842 or triode connected D3A (or other high transconductance pentode) and it is another story altogether.

I wouldn't select a tube with an rp of over 8K with this approach, and considerably lower is better.

That said I use this configuration for output stage drivers where the swing is an asset.
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Old 31st December 2009, 05:14 PM   #13
SY is offline SY  United States
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Especially with a high Rp tube. I recently tried 150H Hammonds on 6FY7 small triode sections (Rp ~ 30k) in a circuit with marginal B+, hoping for more plate voltage. Never made it off the bench, way too much distortion. No free lunch.
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I wouldn't select a tube with an rp of over 8K with this approach, and considerably lower is better.
Agree with both comments. High rp demands high inductance, and high inductance means highly non-ideal. But again, unless I needed the swing, I'd use a good CCS every time.
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Old 31st December 2009, 05:43 PM   #14
tvrgeek is offline tvrgeek  United States
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Red Light District Amp. Very good reading. Thanks.
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Old 31st December 2009, 05:45 PM   #15
rdf is offline rdf  Canada
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Originally Posted by SY View Post
... I'd use a good CCS every time.
CCS'd long tail pair, no silicon-love option this round.

Hi Kevin. I hoped at ~1.3 ma plate current and 8 ma chokes, maybe 40 v p-p swing I could make a run with the Hammonds but the explosion of harmonics was truly an impressive thing. They work a pip moved to B+ filtering duty though.
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Old 31st December 2009, 10:58 PM   #16
kevinkr is offline kevinkr  United States
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Agree with both comments. High rp demands high inductance, and high inductance means highly non-ideal. But again, unless I needed the swing, I'd use a good CCS every time.
I probably should too, in this case though I do need the swing..

Happy New Year!
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