humming noise from JSX head gain channels

[just42dave]

hi just got this amp how do i get rid of the hum from the gain channels the gate kinda works will a noise surppressor or a gate work is it the pre tubes i put a jj in v1 and two tungsols in???can it be modded etc HELP!!!!!! i love the tone just when i stop playing i get this humming and a wowowowow sometimes davydminor@gmail.com

[Mr.WizardNeck]

When you turn it on next, check the blue glow on the power tubes and see if it's flashing. It may be an impedance mismatch. I had a Carvin V3 that had a problem with the impedance switch and there was a helicopter type sound coming from the speakers. I suspect that's what you're hearing and it might be the problem.

[just42dave]

strange i changed all 4 tubes 12ax7,with jjs and when i pull the cord out of amp it sounds like glass hitting if i tap against input or metal part of amp i turned gain channel up and incredible loud piercing fdbk even when playing...i ordered some tubes power tubes from euro tubes a balnced phase inverter too whats the best to use in these i got jjs and tungsols

[just42dave]

will a noise gate like the hush pedal help the hum?

[Mr.WizardNeck]

If it is a problem with your power stage then nothing will silence the problems until you fix it. However, while the amp is on, get something to tap the tubes with that will make a little sound but wont break them (like the eraser at the end of a pencil and see if any of them are microphonic. Replace any that are. It sounds like it may be the case if you can hear it when you tap the amp. That covers that issue/

The wubwubwub thing could be more of a problem though. Can you see your speakers or is it a cloth covered cab? Take the cloth off or whatever you have to do to view the speakers and see if they're pulsing in and out when you aren't playing. If they are, it's probably a problem with the impedance (speaking from previous experience). View the blue glow of your power tubes if taking the cloth off your amp is too much of a hassle to see if they're flashing (did the same thing on the V3).

[just42dave]

thanx

[jb4674]

Take it to a service center and have it rebiased.

Jimmy