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The "Stupid" 6P1P amplifier!
The "Stupid" 6P1P amplifier!
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Old 15th January 2018, 04:34 PM   #21
artosalo is offline artosalo  Finland
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The screen current of 6P43P-E is actually very low and since the output stage is UL-connected, the risk of screen grid overload is much smaller than in case of pentode connection with fixed screen grid voltage.

I am not concerned about exceeding some design-center max. voltage ratings as long as the output stage topology is UL or triode and maximum plate dissipation is kept on sensible level.
These tubes used to work at much higher stress as frame output tubes of bw-tv.
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Old 15th January 2018, 09:35 PM   #22
kodabmx is offline kodabmx  Canada
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And if you use it as a pentode I'd use it at 300V B+. 150V G2.
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Old 16th January 2018, 08:48 AM   #23
Kay Pirinha is offline Kay Pirinha  Germany
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Quote:
Originally Posted by artosalo View Post
I am not concerned about exceeding some design-center max. voltage ratings as long as the output stage topology is UL or triode and maximum plate dissipation is kept on sensible level.
These tubes used to work at much higher stress as frame output tubes of bw-tv.

Yes, in my youth I've cannibalized some old b/w TV's that had a PL84 (series heated equivalent to EL86) as the frame output tube, and I've seen the schematics of many more. But none of them exceeded the 200V Vg2 limit.


I have no concern about exceeding the plate voltage ratings to some extend (up to 350-400 V), as far as dissipation is kept well in it's limits, but due to my experiences a PL84 won't forgive exceeding the screen voltage ratings for a long time.


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Old 16th January 2018, 06:41 PM   #24
TheGimp is offline TheGimp  United States
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The 6P1P is a fairly forgiving tube. I've squeezed over 12W from a pair in UL, and over 3W in SE UL. Higher order harmonics roll off nicely when slightly overloaded.
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Old Yesterday, 02:02 PM   #25
kodabmx is offline kodabmx  Canada
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The 6P1P is forgiving, I've gotten almost 20W out of a pair in tetrode at 340V B+, 56ma bias.


In other news this stupid amp is built. There is too much gain, so I'm going to try about 6db NFB or converting the second stage to a cathode follower. I also need to finish turning the chassis into Swiss cheese, this thing runs hot but that's understandable seeing as plate+heater=240W!


Pics to come later today.
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Old Yesterday, 02:23 PM   #26
Lingwendil is offline Lingwendil  United States
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Old Yesterday, 07:44 PM   #27
kodabmx is offline kodabmx  Canada
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New pics. It's built and it sounds great. And because the tubes are cheap, the chassis was scrap, the power transformer and main cap were surplus, and the output transformers are power toroidals this build was under $150
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Old Yesterday, 08:03 PM   #28
Lingwendil is offline Lingwendil  United States
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Sweet. Shouldn't have any problems with ventilation at least


What part number is the interstage you used? I might want to try some out at some point.

I'm sitting on a dozen 6V6 that are looking pretty good for a similar build... but I want to keep the sockets for the 6SN7 4x4 build I'm finalising... if I do it with 6V6 I have an excuse to order some more Antek toroids though...
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Old Yesterday, 08:55 PM   #29
kodabmx is offline kodabmx  Canada
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I used Hammond 124B.
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