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RE: Opinions please: need recommendations for a Triode driver for a 2a3

Posted by dave slagle on January 17, 2017 at 08:06:47:
OK..

My pre-amp has 27 db / 17.4V RMS output.

That opens up the window to look at tubes with lower gain.

My pre-amp has 27 db / 17.4V RMS output. The pre-amp also has an internal setting whereby I can reduce the output by 6db if necessary. The pre-amp's manual suggests running the output at the lower output level.

Hmmm... if you are only biased at 2.4V and turning it all the way up gives you closer to 15V something is not adding up. Lets assume you get a gain of 15 from your triode 6C6, that menas you need 3V in to get to the 45V bias of the 2A3 but since you are only biased at 2.4V this means your driver will actually hit A2 before it clips the output. This tells me you need more bias and a third battery will start you in the right direction. It doesn't explain the difference between the alleged preamp out and the amp input bias voltage unless your sources only put out a quarter of a volt or less.

I have been using a battery bias on my 6c6 tubes. If possible, I would like to continue to use the battery bias on the new driver tube.

Getting back to the assumption that you can drive this with a clean 10V source. This suggests you can look at the lower gain tubes and possibly even a DHT but as your mu goes down your bias will increase and at some point you *may* find that the stack of batteries becomes a sonic liability rather than an asset. (I found getting over 5V of bias with batteries or LED's to lose the magic and that a tradiitonal RC combo to sound better ymmv)

I would rewire the amp for a 6J5 and see where things end up and then you can explore getting some more bias. As a quickie with the 6C6 you could try lowering the plate resistor. The schematic says 75K and I would cut it to 30-40K so you can keep the current up as you increase bias.

dave