6SC7 To 6SL7 Shared Plate Resistor Question

[rp]

5C8 again, I rewired for a 6SL7 in place of a 6SC7 in V1 but kept the cathodes and plates strapped as for the 6SC7. So far I can't hear any difference in tone and it is a little less microphonic. Question, the 5C8 has the plates on V1 strapped with a 220K resistor, and right now I have both sides set up grid-leak - if I split the cathodes into one triode grid-leak and the other cathode biased can I leave the plates strapped? Unstrapping them creates a lot of problems like an extra cap and somehow connecting to the volume pot.

I noticed in practically all amps using each triode separately they use separate plate resistors, is this simply because those designs want to drive a separate volume pot/channel? i.e. there's no electronic reason not to strap them if one chooses, especially w/ a set up were both triodes won't be used simultaneously?

[martin manning]

I don't see why not. Finding the best bias point will be a little tricky since both sides will be affected. You could start by finding an Rk that puts the cathode voltage back where it was with the grid leak set-up, and experiment from there.

[sluckey]

if I split the cathodes into one triode grid-leak and the other cathode biased can I leave the plates strapped?

Yes. Connecting plates together as in that circuit has been a popular way to mix two signals together.

[rp]

I don't see why not. Finding the best bias point will be a little tricky since both sides will be affected. You could start by finding an Rk that puts the cathode voltage back where it was with the grid leak set-up, and experiment from there.

Hmm, I could see some weirdness. Recall in an other post I noted that the three pre-tubes share one node (using a 5D8 power string) yet the grid leak tube has half the plate voltage (normal as per Fender spec). Will the two sides live happily together? Guess I'll find out.

This poor amp was supposed to be a thoroughbred now it's turning into a mule. I should just keep buying 6SC7s until I find some quiet ones.

[martin manning]

A 2k5 cathode resistor and standard 1M grid leak should put the bias point in the same place, I think...

What are the plate and supply voltages for the 6SL7 wired in with grid leak bias?