CF With Plate Resistor #2

[clyde1]

The title is a reference to an earlier thread in which the OP asked about driving an effects loop from the plate resistor on a CF. Could I derive a signal for a gain stage from the plate resistor and drive the tone stack with the cathode simultaneously without any deterioration in signal quantity or quality?

[R.G.]

Yes, if you are willing to live within the restraints it poses. The same current flows in the plate and cathode resistors. So the signal on the cathode is slightly less than the grid signal, and the plate signal is inverted with respect to the phase of the cathode signal and of a size depending on the ratio of the plate resistor to the cathode resistor. That is, equal plate and cathode resistors give you equal (but opposite) signals. This is how a split load phase inverter works. If the plate resistor is 2x the cathode resistor, the plate signal is 2X as big and so on.

The plate output is higher impedance than the cathode source impedance, so it will not drive as much loading. It also includes any hum, buzz, or ripple that happen on the B+, because it is referenced to B+ and not ground. This can be attacked a number of ways, but it's there. There are other secondary gotchas, too, depending on the application.

[clyde1]

Thanks R.G. So the plate-loaded signal is nothing special in other words, just an ordinary gain stage. I wanted to drive the tone stack with the CF and a reverb stage with the plate but the signal inversion puts a stop to that plan. Just trying to save a triode here and there. Perhaps it might serve another purpose another time.

[pdf64]

I don't see that signal inversion is a significant consideration with regard to a reverb ' wet' signal path?
Even if it was, the signal can be re-inverted back to normality further down the line.
Pete.

[R.G.]

I wanted to drive the tone stack with the CF and a reverb stage with the plate but the signal inversion puts a stop to that plan.

Pdf is right. There's no real concept of "phase" where the signal's going through a long delay. Tiny changes in delay equal huge changes in phase.

Just trying to save a triode here and there.

You might consider using high voltage MOSFETs as source followers where you are using a tube section as a cathode follow. See MOSFET Follies at geofex.com. There are even better MOSFETs these days than when I first wrote that 11 years ago. Replace a couple of CFs, get an entire tube to play with.

[diagrammatiks]

you can just split the signal at the cathode for a reverb.