Champ 12 Problem!

[Kinkless Tetrode 66]

I own a champ 12, recently I change the 12ax7 tubes... Everything worked fine until a few days later, the amp not longer amplifier the guitar... It appears that both of the inputs do not work (nor does the tape input). There is a hum with increases with volume and gain. Could it be that old RCA 6L6 causing the problem? What are your thoughts? Thanks.

[vibratoking]

I'm guessing that one or more of the new tubes are faulty because that is what you just changed. V2 looks common to the guitar and tape input.

[Kinkless Tetrode 66]

Could be, although the GT tubes are generally pretty good... Could it be an internal or jack problem?

[Kinkless Tetrode 66]

Which channel is V2 responsible for?

[vibratoking]

It could be any number of problems. If the amp worked fine up to the point that you changed the preamp tubes, then I would guess those are the culprit. A jack or internal problem would be awfully coincidental. Have you been inside the amp when you changed the tubes or since the tube change? Swap some known good preamps in and see if what happens.

One side of V2 feeds the guitar signal to the output and the other side feeds the tape input to the output.

Is there any signal in the headphone or line out?

[Kinkless Tetrode 66]

Please excuse my ignorance, but is it possible to pull on of the preamp tubes if only the drive channel is used?

[Kinkless Tetrode 66]

Yes there is a stereo headphone output and a 1 volt line output...

[vibratoking]

Yes there is a stereo headphone output and a 1 volt line output...

Does that mean you hear a normal guitar sound coming out of the headphone output?

It also looks like the tape input should be functional with V1 removed. You could try that and also try swapping the two tubes.

[Kinkless Tetrode 66]

There is no sound coming out of the headphone - just hum and hiss