| Author | Message | ||
     Eric Schold |
I've got a 1978 HD 130 which seems to be working fine until twenty or thirty minutes into playing when it suddendly doubles in output, which I'm sure is the output it should have from jump street. It will then fluctuate up and down with further playing. Anyone experienced this or have any clues? | ||
| michael kaus |
Sound like a flaky tube. Does it get real distorted as it get louder? If it does, your bias voltage might be flaky. Is this the 12ax7 model or the SS driver model? Mike. | ||
| Eric Schold |
Thanks for the reply Michael, this amp has a solid state pre-amp with a single 12ax7 phase splitter. When it gets louder, it gets much cleaner also. The output tubes were recently replaced and biased to try and resolve the problem, but had no effect. | ||
| Steve Kennedy |
If the 12AX7 phase splitter tube is replaced with a known good one and the problem still occurs, I would be looking for an intermittent in the power supply or the preamp. It is also possible that you have a thermal intermittent short in your output transformer which cannot be remedied short of a complete replacement or rewind job. Steve |