SF Princeton Reverb - too bright!

[nickb]

What's the advantage of a cap plate-to-grid as opposed to plate-to-ground - no impedance 'drag' on the plate?

A small cap from plate to grid, because of the amplification of the tube, acts like a much bigger cap from grid to ground (miller effect). Therefore the knee frequency depends on the source impedance. This might be a problem in the V1 position if you change instruments as you might not get the result you expected as the guitar impedance differs. A cap from plate to ground does not suffer from that problem. Not that it, practically speaking, makes a big difference.

[Justin Thomas]

I've been experiencing some of this same thing. I don't have a scope, and am willing to just do some experimenting. As I understand it, the small cap would go from plate to cathode in my case - an EF86. That would eliminate the possibility of getting DC on my guitar in case of a shorted cap, yes? I could also try plate to ground, right?

Also, the silverface caps from grid to ground on the output tubes?

Also was wondering - the Vox/Matchless cut control - that basically lets the highs coming out of the phase inverter cancel each other out, correct? Same with the Crossline MV - shorts two out-of-phase signals together to varying degrees, right? So, any reason a tiny cap across the PI could accomplish a similar goal?

I'm not asking you all to tell me the outcome, and am willing to do the exercise to find out. But "experimenting" without burning down my house or my transformers is the reason I ask... shall I go ahead and try? Failure is ALWAYS an option, as long as nothing expensive burns up!

Thanks,

Justin

PS: No, I don't have a scope and a sig-gen, just a nice MM & a sense of adventure.

[nickb]

I've been experiencing some of this same thing. I don't have a scope, and am willing to just do some experimenting. As I understand it, the small cap would go from plate to cathode in my case - an EF86. That would eliminate the possibility of getting DC on my guitar in case of a shorted cap, yes? I could also try plate to ground, right?

If the cap were to fail, and it's seldom they go dead short, grid one would conduct the current to ground. Also limited by the plate resistor, and the voltage would be limited to just a few volts. It's not a worry. You could always add a cap in series with the input anyway.

Also, the silverface caps from grid to ground on the output tubes?

for small caps I wonder that the primary reason would be stability rather than tone. For bigger ones It's very similar to the next item...

Also was wondering - the Vox/Matchless cut control - that basically lets the highs coming out of the phase inverter cancel each other out, correct? Same with the Crossline MV - shorts two out-of-phase signals together to varying degrees, right? So, any reason a tiny cap across the PI could accomplish a similar goal?

There's nothing special here. It''s just a cap between two signals which presents a low impedance at higher frequencies.

I'm not asking you all to tell me the outcome, and am willing to do the exercise to find out. But "experimenting" without burning down my house or my transformers is the reason I ask... shall I go ahead and try? Failure is ALWAYS an option, as long as nothing expensive burns up!

Thanks,

Justin

PS: No, I don't have a scope and a sig-gen, just a nice MM & a sense of adventure.

When overdriven things get complicated. You may well find differences in that case between the different methods.