So a friend who rents out backline equipment has a weird issue with an amp:

"One of my Fender Twins is volume swelling on the vibrato channel. I'm having trouble finding info on it. I'm guessing it's that goddamned light, but maybe an input tube? Ever heard of this?"

Anyone have anything I can tell him before I just make him take it to the amp experts in town?
This comes with virtually no knowledge, but I would try swapping around preamp tubes.
RG351DX - Bridge Dragonfire Screamer, Mid+Neck Fender Hot Noiseless
Peavey Valveking 112 - Eminence GB128
AMT E1 > Joyo AC Tone > Dan'o EQ > Shimverb > Digidelay
Hmm...never heard of that before. Usually the problem with the Vibrato is that it just doesn't work anymore.

When in doubt, swap out 12AX7s.

Probably just V2 or V5 going.

Are you sure it's only on the Vibrato channel?

If anything is wrong with a tube amp, swap preamp tubes, then ask questions. They're cheap enough, and usually the culprit of problems.
Spin 'round carousel when your horse isn't screwed in.

My band:
Fractured Instinct
(For fans of Death/Groove/Prog Metal)

Ibanez RGA42E
Ibanez S420
LTD H-301
Ibanez RG520
Peavey Predator USA
Douglas Grendel 725
Line 6 Pod HD500X
Last edited by Offworld92 at Nov 18, 2013,
What he said ^.
V2 is the input tube for the vibrato channel and V5 is the actual vibrator.
Gilchrist custom
Yamaha SBG500
Randall RM100 & RM20
Marshall JTM45 clone
Marshall JCM900 4102 (modded)
Marshall 18W clone
Fender 5F1 Champ clone
Atomic Amplifire
Marshall 1960A
Boss GT-100

Cathbard Amplification
My band