T
timthetortoise
MADE OF SANDALWOOD
Okay, so here's the deal. My band's guitarist just got an MX VTX head. We tried it out and it seemed alright, except the sound was a bit muddy. Checked the tubes, and they were old GEs. So obviously needed to replace those. Figured it'd need a cap job too so added that to my list. So we're going through practice, everything's fine, and then bam! Fuse blows. There wasn't a loud pop or anything like that so I figured not a big deal.
So I bring the amp home, get the caps all replaced, put some new tubes in. Today I bring it up and power it on. I let it warm up and take it out of standby. What greets my ears is a loud hum accompanied by intense blue in one of the tube pairs (it's a quad). So I figured it was a grounding issue. Went through and double/triple checked every cap I touched. Traced grounds, checked for leaks, checked voltages, continuity, the whole nine yards. Everything checked out fine. So I figured I better not test on new tubes in case the overload would damage them. Put the old tubes back in and power on. And guess what! One of them didn't heat up! So now I'm a little bit worried about what could have gone south with that tube. I checked the voltages on the tube board while powered on, and the voltages on two pins (I believe it's the grid side but don't know much about pin arrangements yet) are significantly less than that of the other side.
So I traced the input for that side's pins and it led to one of two power transistors.
So my question is: would a faulty transistor do something like this? I was set on the problem being a ground or power issue in the preamp, but when I pulled the pair from the troublesome sockets, the amp ran fine. I'm not an amp tech by any means but would like to be able to resolve issues like this myself, so any guidance other than "take it to a tech" would be appreciated.
So I bring the amp home, get the caps all replaced, put some new tubes in. Today I bring it up and power it on. I let it warm up and take it out of standby. What greets my ears is a loud hum accompanied by intense blue in one of the tube pairs (it's a quad). So I figured it was a grounding issue. Went through and double/triple checked every cap I touched. Traced grounds, checked for leaks, checked voltages, continuity, the whole nine yards. Everything checked out fine. So I figured I better not test on new tubes in case the overload would damage them. Put the old tubes back in and power on. And guess what! One of them didn't heat up! So now I'm a little bit worried about what could have gone south with that tube. I checked the voltages on the tube board while powered on, and the voltages on two pins (I believe it's the grid side but don't know much about pin arrangements yet) are significantly less than that of the other side.
So I traced the input for that side's pins and it led to one of two power transistors.
So my question is: would a faulty transistor do something like this? I was set on the problem being a ground or power issue in the preamp, but when I pulled the pair from the troublesome sockets, the amp ran fine. I'm not an amp tech by any means but would like to be able to resolve issues like this myself, so any guidance other than "take it to a tech" would be appreciated.