amp buzz

[Jason01]

Hey there experts, my amp (tube 2x12 combo) has a buzz to it, like a bad ground somewhere or something. Anyone got any tips on how to go about problemsolving this that doesn't end up with me being extra crispy or owing alot of money to the nearest repair shop (like 70 miles away?)

[FrankieIII]

Brand/model is?

[gtone]

Buzzing all the time, just at idle or just when you play certain things?

[Jason01]

VHT pittbull classic, buzzes from the minute the tubes warm up til you shut the thing off.

[Bobby Marshall]

Try different guitars, different cables (go direct from guitar to amp). If you have an effects loop, see if the buzz comes through the signal in the effects loop, if it does then it should not be the power section causing the issue. Swap out new preamp tube one by one through preamp section. If preamp section not causing, then new power tubes may be needed. Also, you could have an issue with the power where you use the amp. Did you bring to a buddies house and try there? Where I rehearse I get noise but noise free at gigs and my home.

[anotherfreak]

try turning in a circle w/ yo' guitar

solved many problems recording that way, live it's too loud to care(hopefully)

[crunchee]

_{Try different guitars, different cables (go direct from guitar to amp). If you have an effects loop, see if the buzz comes through the signal in the effects loop, if it does then it should not be the power section causing the issue. Swap out new preamp tube one by one through preamp section. If preamp section not causing, then new power tubes may be needed. Also, you could have an issue with the power where you use the amp. Did you bring to a buddies house and try there? Where I rehearse I get noise but noise free at gigs and my home.}

_{try turning in a circle w/ yo' guitar}

_{solved many problems recording that way, live it's too loud to care(hopefully)}

_{+1 to both! It's fairly easy to rule out external variances with the power supply/wall voltage, as well as the amp being noisy depending on the position of the guitar in relation to the amp. Plus, ruling this stuff out don't cost nuttin'. Are you using humbuckers? Single coils?}

[FrankieIII]

Have you tried it with a different guitar, or tried the same guitar into another amp plugged into the same outlet, to rule out the guitar and cord?

Did it used to be quiet when plugged into the exact same outlet with the same guitar?

Is the outlet grounded it's plugged into?

How old are the preamp tubes?

Is there a computer and/or computer monitor close to the amp and turned on?

Is there fluorescent lighting turned on close to the amp?

Does the amp have a ground switch on the back to change?

[Jason01]

Lots of choices to try, I know I've tried the ground switch with no success. There is a computer nearby, my outlet tester says its wired correctly. When I first got the amp it was very quiet but now it buzzes as soon as the tubes heat up(at home or at practice place). I've tried a number of different guitars through it and a few different cables, I've even tried walking in circles (which does help with my practice amp-that ones right next to the computer) but no luck. I dont have any spare tubes to I'll have to pick up a few and start swapping tubes I guess.

[Steve Haynie]

Get a fuzz pedal and it will mask the amp buzz.

[Jason01]

then itll go FFFUUUZZZZZZZZZZZZZZZZZZZZ

[seeker]

It's possibly a preamp tube. Find V1 and V2 and swap them. It the noise level changes (especially downward) it's probably the V1 preamp tube. It's possible that both have gone noisy to the same degree, but not likely.

[Jason01]

I just noticed I am missing the tube shield on the V1 tube. Would that cause the buzzing?

[Jason01]

Ok, I think I may have some incompatible tubes in this amp.

recommended - currently in the amp

V1 12ax7wb - 12ax7wb

V2 12ax7 china - 12ax7R (groove tubes)

V3 12ax7 china - 12ax7EH (russia)

V4 12ax7 china - 12ax7A (mesa)

V5 12ax7wb - 12ax7EH (russia)

V6 12at7 china - ECC 83 (yugoslavia)

V7 12ax7 china - 12ax7EH (russia)

V8 12au7 china - 12AT7 (groove tubes)

V9-12 EL-34 svetlana - EL-34 STR 447 (mesa)

I am really concerned about V8 because in the VHT pdf it states in BIG BOLD LETTERS that V7 and V8 are not interchangeable with other tube types. Am I doing damage to the amp running these tubes?

[anotherfreak]

You are safe running any 12ax7 for another, the EH, WB, LP, SP, A, R, are just model/make differences. They are all 12ax7 tubes. The 12at7 might be a little "hotter" than the 12au7 though, I'm betting that's the 'verb or effects loop,

[hamerhead]

Make it stop smoking pot.

[Jason01]

http://www.vhtusers.com/documents/CLASSIC%20COMBO%20REVERB.pdf

Heres a link to the amp pdf from VHT. It says V8 is voltage amp/driver. I'm not sure what that means but it sounds important!

[seeker]

Ok, I think I may have some incompatible tubes in this amp.

recommended - currently in the amp

V1 12ax7wb - 12ax7wb

V2 12ax7 china - 12ax7R (groove tubes)

V3 12ax7 china - 12ax7EH (russia)

V4 12ax7 china - 12ax7A (mesa)

V5 12ax7wb - 12ax7EH (russia)

V6 12at7 china - ECC 83 (yugoslavia)

V7 12ax7 china - 12ax7EH (russia)

V8 12au7 china - 12AT7 (groove tubes)

V9-12 EL-34 svetlana - EL-34 STR 447 (mesa)

I am really concerned about V8 because in the VHT pdf it states in BIG BOLD LETTERS that V7 and V8 are not interchangeable with other tube types. Am I doing damage to the amp running these tubes?

Grack, you've got a couple of differences. FIRST AND FOREMOST, the V8 is way off. Replace that 12AT7 with a 12AU7 immediately The 12AU7 and 12 AT7 have vastly different gains; 20 vs 60. You've got three times the gain you should have in that spot.

Then change your V6 reverb driver. ECC83 is the european designation for a 12AX7, which has a gain of 100 (nominally). It should be a 12AT7 (60 as above). Try out the 12AT7 you removed from the V8 spot.

As far as the warning, I can only assume the design is highly dependent on the gain values provided by the specified tubes in those spots.. You can "cool" an amp down by dropping a 12AT7 in the preamp (V1-ish) spots in lieu of a 12AX7. But the phase inverter (V7) usually directly feeds the power tubes. Have -no- idea what the Voltage Amp Driver (V8) is though.