that is a fairly accurate description...

yes, you have hit on it...the pot is o.k., but the hiss increases when the treble is boosted, even with no volume on the controls. i don't have a schematic, and i haven't come up with anything definite by scanning over the pc boards...there are a couple of small transistors on the same board as the pots, and you can see that the emitters are grounded along with the pots, but i'm not sure of much else at the moment.  this amp uses 2 power transistors.  i need to delve into it further...this is a mcgohan model ms-203, 20 watt p.a. head.  THANKS FOR THE REPLIES! 

hey y'all...i recently got a mcgohan p.a. at a sale for a buck...it works, but when you turn up the treble, it reveals an annoying hiss, even with all volume knobs turned to zero. i replaced the one carbon comp resistor it had, but no change.  it has a small (.001uf)ceramic cap as the last component before the treble pot...any chance this is the problem?  any suggestions?   thanks!