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Hi all. Here goes...
I have a VHT 50/12 combo amp with switchable class a/b - class a operation. So recently the amp started to sound a bit strange and realizing that my power tubes were ancient I decided to replace them. After doing so the amp sounded perfect and life was great. A few days later, though, the amp starting sounding odd again (farting/weird rumble/crackling/etc.). I had a handful of tubes lying around so I replaced each preamp tube one by one for troubleshooting purposes... no luck. I then went as far as replacing the reverb tube, phase inv tube and rect tube, just because I had extras and I was curious. Because nothing seemed to help so I put all the original tubes back in (with the brand new power tubes) and was at a standstill. After playing for 30 minutes one night the DC fuse blew and the amp smoked out. It seemed a cap (47uf/100v) on the power supply board blew up. I checked all the rect diodes (per a friend's suggestion) and they were fine. I replaced the cap and the amp fired back on with no issues.
So here's the problem: the amp seems to work OK in class a mode, but it only works for about 10 minutes until a fuse blows. In class a/b mode the amp won't pass any sound other than some faint, broken-sounding garbage, and only when it's cranked. What's more is, when I throw a meter on the power tubes in class a/b mode, nothing registers on the meter unless it's cranked. Even then it's maybe 3ma. In class a mode, the meter registers what it should.
The bottom line is I know just enough to be dangerous, but I'm starting to realize this may be for a pro. Just thought I'd see if anyone had any suggestions before spending the cash to get it fixed.
Sorry for the lengh... thanks for the help.
I have a VHT 50/12 combo amp with switchable class a/b - class a operation. So recently the amp started to sound a bit strange and realizing that my power tubes were ancient I decided to replace them. After doing so the amp sounded perfect and life was great. A few days later, though, the amp starting sounding odd again (farting/weird rumble/crackling/etc.). I had a handful of tubes lying around so I replaced each preamp tube one by one for troubleshooting purposes... no luck. I then went as far as replacing the reverb tube, phase inv tube and rect tube, just because I had extras and I was curious. Because nothing seemed to help so I put all the original tubes back in (with the brand new power tubes) and was at a standstill. After playing for 30 minutes one night the DC fuse blew and the amp smoked out. It seemed a cap (47uf/100v) on the power supply board blew up. I checked all the rect diodes (per a friend's suggestion) and they were fine. I replaced the cap and the amp fired back on with no issues.
So here's the problem: the amp seems to work OK in class a mode, but it only works for about 10 minutes until a fuse blows. In class a/b mode the amp won't pass any sound other than some faint, broken-sounding garbage, and only when it's cranked. What's more is, when I throw a meter on the power tubes in class a/b mode, nothing registers on the meter unless it's cranked. Even then it's maybe 3ma. In class a mode, the meter registers what it should.
The bottom line is I know just enough to be dangerous, but I'm starting to realize this may be for a pro. Just thought I'd see if anyone had any suggestions before spending the cash to get it fixed.
Sorry for the lengh... thanks for the help.
, comfortable, on a well illumuinated place.
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