MKIV Reverb Sounds Like An Auto-Wah

[ruso]

So I recently picked up a six month old MKIV medium head and have been spending the last few weeks dialing in some bad-*** tones. I'm typically not one for reverb but since this is the fist amp I've had in years with reverb, I though I would give it a try...

Well, for some reason, when I turn up the reverb, I get an "auto-wah" type of effect the harder I pick. It sounds really really bad. Does anyone think there something wrong with the reverb box or possibly the tube?

 

[Platypus]

I'd check out the tube first.

 

[Buddy]

Wacky oscillation ? , sounds like a bad tube or a resistor gone out of spec .