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Hi guys,
I had a similar post on another link. But I'm starting a new one because I had some inaccurate info. I put down that the amp was motorboating. that wasn't the case. It's doing some kind of instability but not motorboating. Here's what happens:
Play on the Vibrato channel at any volume. No problems. Now:
Play on either channel and turn the Normal channel's volume to 10 and sound goes away completely and all I hear is a hum. Not only does it stop just the normal channel's sound, but it also stops the sound from comming out of the Vibrato channel. It pretty much kills the amp. And here's why... (I took some measurements this time).
Right as the volume on Normal channel hits 10 (9 still works just at the max out point on the pot-and I tried a new pot, that wasn't it), but as the volume on Normal hit's 10, it throws the phase inverter off balance. I measured the plate voltages on both sides of the 12at7 when the amp was stable and they're both 240VDC. Then I measured when the volume is at 10 on the Normal Channel and one side is at 250V and the other at 200V.
So... for some reason the volume on channel 1 is really throwing the amp into something funky. I pulled the first tube and tried the proceedure (turned the normal up to 10) and of course it didn't do the problem anymore. since that removes all gain from the normal channel. So... Something weird here. Any ideas?
I replaced the original power supply and bias supply. That didn't do Anything.
Thanks!
Nick
I had a similar post on another link. But I'm starting a new one because I had some inaccurate info. I put down that the amp was motorboating. that wasn't the case. It's doing some kind of instability but not motorboating. Here's what happens:
Play on the Vibrato channel at any volume. No problems. Now:
Play on either channel and turn the Normal channel's volume to 10 and sound goes away completely and all I hear is a hum. Not only does it stop just the normal channel's sound, but it also stops the sound from comming out of the Vibrato channel. It pretty much kills the amp. And here's why... (I took some measurements this time).
Right as the volume on Normal channel hits 10 (9 still works just at the max out point on the pot-and I tried a new pot, that wasn't it), but as the volume on Normal hit's 10, it throws the phase inverter off balance. I measured the plate voltages on both sides of the 12at7 when the amp was stable and they're both 240VDC. Then I measured when the volume is at 10 on the Normal Channel and one side is at 250V and the other at 200V.
So... for some reason the volume on channel 1 is really throwing the amp into something funky. I pulled the first tube and tried the proceedure (turned the normal up to 10) and of course it didn't do the problem anymore. since that removes all gain from the normal channel. So... Something weird here. Any ideas?
I replaced the original power supply and bias supply. That didn't do Anything.
Thanks!
Nick
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