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12P17L or 2P29L In Pentode As Output Tubes In Amp?
12P17L or 2P29L In Pentode As Output Tubes In Amp?
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Old 18th July 2020, 04:29 PM   #1
FlaCharlie is offline FlaCharlie  United States
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Default 12P17L or 2P29L In Pentode As Output Tubes In Amp?

I've seen posts about the 12P17L, which is basically an indirectly heated version of the 4P1L. But they all seem to be using them in preamps wired in triode. My interest in these is, in part, because, being indirectly heated, they presumably don't have the issues with microphonics which the 4P1L has and could be heated with AC.

Anyone try them in pentode as output tubes in an amp? Yes, I know they will be less linear.

I'm considering either a breadboard experiment or maybe dropping them into a vintage console amp chassis. This is mostly out of curiosity so simple, cheap and junkbox parts are the order of the day.

I saw one post by Wavebourn in which he mentions a vintage farm radio that put out 10w using PP 12P17L. In PP, what OPT primary impedance would be best and how much drive would be needed in order to get 8-10w per channel? And what operating points?

I've also seen some discussion about the 2P29L, which is a directly heated pentode but, again, only used in triode for preamp duty. I did try the 2P29L last year when I was breadboarding preamps and it sounded very good. Part of its appeal is that, despite being directly heated, it seems to be immune from microphonics.

Anyone try them in pentode as output tubes, either SE or PP? How much power output could I expect? Again, what OPT primary would be suitable and what operating points?
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Old 25th July 2020, 01:02 PM   #2
FlaCharlie is offline FlaCharlie  United States
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I thought that surely someone on here would be able to offer some advice about using these as output tubes in pentode, particularly the load and drive requirements.

Presumably, at least in the case of the 12P17L, that is what they were designed to do. @Wavebourn commented on their use in a Soviet radio.
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Old 1st August 2020, 12:20 AM   #3
Wavebourn is offline Wavebourn  United States
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12P17L or 2P29L In Pentode As Output Tubes In Amp?
So, what is the result of your breadboard experiment?
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Old 1st August 2020, 01:24 PM   #4
FlaCharlie is offline FlaCharlie  United States
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Quote:
Originally Posted by Wavebourn View Post
So, what is the result of your breadboard experiment?
Thanks for the response . . .

For now, my breadboard setup has been dismantled so I have not done anything with either of these tubes as pentode outputs.

I'm interested in trying them, though, particularly the 12P17L in PP. Trying to figure out if I have any suitable OTs in the junkbox. And what their drive requirements would be.

If you mean the 2P29L preamp. Here's a thread I posted about it last year. You made some comments about the history of these tubes, as I recall.

2P29L Preamp
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Old 3rd August 2020, 12:52 PM   #5
FlaCharlie is offline FlaCharlie  United States
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Here's the data sheet for the 12P17L. Unless I'm missing it, it doesn't seem to include any info on a suitable OT load.

I assume it was not intended to be used as an audio output tube. Perhaps that info can be extrapolated from the data sheet?

Again, I'm most interested in using it in PP. Trying to figure out if I have any suitable OTs and what driver tube(s) might work.
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