Cap from plate resistor to ground

[rocketeer]

Included is a pict of the V2 and V3 gain stages in a recto. I know on V3 the cap across the plate resistor is to dump high end (snubber). What is the cap on V2 doing. Is it placed close to the tube to increase high end transients on that stage or something else? Technically it's in the same node as V3 so does it affect that stage also? Would it be advantageous to place a diode ahead of its connection point to isolate it from other stages in that node? What are the effects of increasing or lowering the value?

Always wondered this and I haven't been able to find info on it. Thanks all!

[jjman]

In that scheme it's acting as a filter cap. Could be supplementing the main filter cap(s) on that node. I know people do that on cathodes sometimes.

[Super_Reverb]

What is the cap on V2 doing. Is it placed close to the tube to increase high end transients on that stage or something else?

The cap you point out is a bypass cap. It's a localized filter cap to bypass AC to ground as close as possible to plate circuit. Due to wire inductance between electrolytic filter cap and plate load resistor, this is a good idea, but not required. Typically a 0.01 to 0.1u is used.

You see this on switching and other high speed logic circuits - caps as close a possible to p/s pins in order to provide instantaneous current needs to circuit.

cheers,

rob