Amp hum

[cryptic Kitten]

It's on my 3120 again/still. Had all the tubes replaced and it sounds better but still not so great. The hum is volume dependent. If i change the volume on the guitar or the amp the hum changed. Zero volume = Almost no hum. It still makes the hum when nothing is plugged in and the volume is up. I think the guy didn't change one of the preamp tubes. Maybe the PI? Do I need a power conditioner or noise gate or is there something I could still do to fix this? I don't have money to keep throwing at this amp so I need to know what I do will work.

[Reeltarded]

Everything is a guess. What did he say about it?

It is so impossible to diagnose the exact problem withiut being there. It it filter caps? A wire out of place? A poor ground? A problem with the board? Does this model amp have a knack for humming? Is it caused by your house AC? Is it RF or line induced from another device plugged into the AC?

Hummmm..

Does it have a loop? Plug another preamp or a drive pedal into the return and play with it. Still humming? Have another power amp? Plug the send into it and see if it hums.

[cryptic Kitten]

He said the amp wasn't buzzing at all after he changed the tubes so I was wondering if it could be my power?

[Reeltarded]

Yeah, it could be anything and $200 later it could still be that same thing if you just don't know..

[LeftyStrat]

Any compact fluorescent lights nearby? Or light dimmers?

Both can cause buzz in an amp.

[cryptic Kitten]

I moved it out into another room where there is only 1 little light with no dimmer. Still the same thing. I should mention the thing squeals if I turn the gain past noon.

[Dr-Joned]

Try a different cord, a different guitar?

[cryptic Kitten]

It does it without the cable being plugged in as well. Would a micophonic preamp cause it?

[JazzGuitarGimp]

It does it without the cable being plugged in as well. Would a micophonic preamp cause it?

More likely an improperly-wired input jack than a microphonic tube. If the tip switch is not wired to GND, the amp will definitely hum when the volume is increased with nothing plugged in.

[sepulchre]

It squeals when turned up past noon . . . with nothing plugged in? No guitar or cord?

[cryptic Kitten]

No, it hums with the guitar not being plugged in. That howling squeal sound thing only happens if the guitar is plugged in.

I cranked the volume an tapped the amp head and it didn't make any noises through the cab. I tapped the preamps and I think v3 might be a little microphonic?

[cryptic Kitten]

Another thing is the guy didn't give me back my power cable. I found another one that was 120vac so I figured that should work and won't make a difference?

[sepulchre]

I'm sure it'll work fine, but go back and get your cable from him.

[Structo]

Check out the input jack and make sure it shorts to ground when nothing is plugged in.

Also check the grid leak resistor (typically 1Meg)

[cryptic Kitten]

Check out the input jack and make sure it shorts to ground when nothing is plugged in.

Also check the grid leak resistor (typically 1Meg)

Are either of those things I could do without much experience? I hear a lot of people on here talk about getting electrocuted so hard you end up on another planet.