Caps across plate resistors

[karl82]

In some express schematics Ive noticed sometimes there are capacitors across the plate resistors in the preamp section. How do these effect the sound?

[Sonny ReVerb]

I found a possible explanation here:

http://www.booyaka.com/~al/audio/theory ... theory.txt

Here's the pertinent section:

In many super high gain preamps you'll find very small bypass caps attached to the plate resistors. These caps allow extremely high frequencies that might cause "squealing" to pass around the plate resistors and out of the signal path.

The B+ rail acts as an AC 'ground' in this case.