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Original Message

RE: 20B

Posted by banpuku on January 18, 2017 at 16:27:59:
Update as of 1/18/17:

I spent the day migrating the amp back to the 6C6 pentode driver. Listening carefully. Then migrating back to the 6C6 triode strapped. I can say with confidence that I prefer the 6C6 triode strapped. The noise floor is lower, which results in a much deeper soundstage. High and mid frequencies have greater texture and a smoother presentation. So, I want to continue on my quest to implement a triode driver for the 2a3 output tubes.

Thank you to those who have posted their input so far.

Here is where I stand and question that need to be answered:

1. The only issue with using the 6C6 triode strapped is that to get near full output, the preamp volume knob needs to be turned all the way up. With the preamp at full throttle, the output is about 90% of max output (just a guess, but close enough for the sake of this conversation). So, is there a way to get the 6C6 triode configuration to get more output from the power amp? If so, how?

2. The 20B driver tube has an amplification factor of 20. The 6C6 data sheet says that the 6C6 has an amplification factor of 20 in Triode mode, and does not list an amplification factor for pentode mode. So, is an amplification factor of 20 enough gain and therefore the 20B might be a suitable driver? Don't know, but your input would be appreciated. I have a near ready schematic of the 20B --> 2A3. Going with this solution requires more $s and modifications. The 20B --> 2A3 requires either a plate choke or a plate transformer that acts as an interstage transformer.

Ideally, we would find a solution to option (1) and if it works nicely, then I could move towards a more permanent solution (2) that leverages the choke and possible interstage transformer.

Any input would be appreciated.

Thanks,
Pat