Weird MKIIC hissing

[doctorgonzo69]

I've got the 60 watt version, with reverb and EQ. It occurs in the Rhythm channel whenever the "Master" is cranked above five or six and gets louder as you crank the Master towards "10". It will make an ominous but intermittent hissing sound, but will disappear instantly if I switch back and forth between Rhythm and Lead, or if I switch the amp from "Standby" and back to "On" quickly. It's not too **** intrusive, but still...
Any help would be appreciated.
dg69

 

[Tuna141]

The first thing I'd check are the preamp tubes. Try swapping them around to see if the hiss switches to your other channel or you notice that the hiss has gone away or sounds different.

Better yet, if you have a spare, try swapping it with each preamp tube one at a time.

Good luck.

 

[doctorgonzo69]

Thanks, I'll give it a shot!