Tube preamp for SS amp

[printer2]

Tomorrow I might look at this differently, but tonight it makes sense to me. So other than I have not worked out the actual values for biasing, am I missing something? I have a small amp I built using a car stereo amp as the power section but the SS preamp was not doing it for me. I am thinking I should get 2-3V swing off the cathode which should be plenty to drive the amp.

[Steve Conner]

Why do you have feedback going to the screen in the second stage? Some sort of variable triode/pentode control?

I'd be inclined to take the output from the second stage plate using a voltage divider. The required signal already appears at the top of the 1M screen feedback pot, so just hook a 100k resistor from there to the top of your 10k master volume pot. (after disconnecting it from the cathode of course)

If you do take the output from the cathode, you'll need a DC block capacitor to prevent the pot from scratching.

[printer2]

Now how did I forget that cap?

Yes it is a pentode to triode control, thought I would try it but have it on board rather than a control on the panel. Normally I would just take it off the plate but with the low input impedance of the amp I thought this might work out. I was on the fence on this so that is why I posted this.

[ReadyTeddy]

Isn't the 100k plate resistor in the 2nd stage a problem when paired with a 220 ohm cathode resistor? Think of it this way, a 1V P-P output on the cathode will try to drive the plate 450V P-P, causing the tube to saturate.

[printer2]

Isn't the 100k plate resistor in the 2nd stage a problem when paired with a 220 ohm cathode resistor? Think of it this way, a 1V P-P output on the cathode will try to drive the plate 450V P-P, causing the tube to saturate.

In my opening post I said I did not do any biasing of the tubes yet, in the past I have found that you can find a sweet spot by ear. I was just doing a quick copy and past from other schematics I have, should have changed the value I guess. I just was not sure if I wanted to run the tube with higher or lower current or what voltage. I was mainly wondering about running the SS amp from the cathode and what people thought.