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Tubelab Discussion and support of Tubelab products, prototypes and experiments

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Old 29th October 2011, 12:05 PM   #11
Treybal is offline Treybal  Chile
diyAudio Member
Join Date: Mar 2011

I'm just finish assembling my tubelab simple se:


This is my very first amp proyect, and after reading as a noob, and see the wiring page at the tubelab's site don't know how to wire this in pentode mode.

I think that perhaps connecting R18 and R28 to the B+ would do, but i'm totally unsure, this idea comes from wikipedia's deffinition of pentode mode.

So, how can i make that connection?

Today i'll get all the transformers from a local shop (custom made) and the choke.

Thanks in advance

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Old 4th November 2011, 03:26 AM   #12
w5jag is online now w5jag  United States
diyAudio Member
Join Date: Feb 2007
Location: Arkansas
I don't have a board in front of me, but from memory T3 Pri:2 and T2 Pri:2 should be jumpered to T3 Pri:1 and T2 Pri:1 for triode operation, or T3 Pri:3 and T2 Pri:3 for pentode operation. It is much easier to get the amp running in triode configuration.

I've been running my SSE in pentode mode for more than a year with good results, mostly with low screen voltage sweep / rf tubes, with good results. I have also used the EL34 with good results, albeit at relatively low screen voltages.

Be advised that, imo, pentode mode does require more negative feedback than the onboard cathode feedback can provide, at least in my setup. Without negative feedback, the frequency response will be skewed to favor the high frequencies,

More can be found in the 6146 in the SSE thread, if you are interested.

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Old 4th November 2011, 11:42 AM   #13
Treybal is offline Treybal  Chile
diyAudio Member
Join Date: Mar 2011
Thanks, i'm gonna start with triode mode to get the amp running. I'm doing the basic configuration with a 375-0-375 power transformer, so i could get a >400 V B+, perhaps thats not provide low screen voltage, what's your low screen voltage and your B+?
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