Can a dual triode use a common cathode resistor?

[bluegti]

I'm working on the layout of my circuit and noticed that its getting crowded on the tube socket. Then I thought, "I wonder if I can use a common cathode resistor."

I'm using half of a 6SN7 as the driver for each channel in a stereo amp. The cathodes of each triode are pins 3 and 6. Can I connect pin 3 to pin 6, then use a common cathode resistor and bypass cap (see attachment)? If so, do I use the same value resistor (e.g. 1.6K) or would I need to double or halve it?

BTW. This is the first amp I've ever "designed" by myself. Admittedly, there are other very similar circuits out there, but I am looking at the grid curves and doing the math myself so I'm not looking for suggestions of "better" circuits to use. I just want to know if I can do this or is it a really bad idea.

Thanks!

 

[OneyedK]

Yes, you can, but use a very good decoupling cap, otherwise your channel separation will suffer...

Same cathode voltage > double cathode resistor current > 1/2 resistor value. (800 Ohm in your case)

 

[pointy]

thats not crowded.......................this is crowded (see link)

 

[Eli Duttman]

Double the bypass cap. value and halve the resistance value. The remark about a high quality part in the bypass cap. position is correct. That cap. is now a common path to ground. Use nothing of a grade less than a Nichicon KZ.

If possible, switch to a LED stack for bias.

 

[bluegti]

Yes, you can, but use a very good decoupling cap, otherwise your channel separation will suffer...

Same cathode voltage > double cathode resistor current > 1/2 resistor value. (800 Ohm in your case)

By "very good decoupling cap", are you referring to the capacitor in my diagram that is in parallel with the cathode resistor? I thought this was called a "bypass cap".

Or, are you referring to the caps going between the plates of the driver (pins 2 and 5) and the grids of the power stages? I thought these were called "coupling caps".

Can you suggest a "very good" cap?

Thanks!

 

[alexg]

The Zen amp (SE EL84) have a common cathode resistor for the power tube and it sounds good.