Sound Quality

[old_coot88]

If it's a 2-position switch, it's a simple treble-cut circuit using a single cap that's switched in or out (i.e., on/off). You can reduce the value of that cap till you find one that gives the tone you like best.

The cap usually goes to the plate of the output tube.

OOPs didn't see your last post. A .1 will definitely muffle it. A .01 or thereabouts would be more in the ball park.