Howdy. If I understood correctly. My DIY tube stereo PA does that. Signals go down as the power tubes heat up and start working. The neg. feedback kicks in lowering the driver signal levels. I never use global neg. feedback. I take the neg. fb. from the end tube anodes in my builds. It seemed to me that the signal also got pointy when the end tubes began working. That would suggest biasing problems. One might check the anode voltages without and with the end tubes inserted. If the voltage drops a lot it could be indicative of one end tube drawing much current. There might be red plating of the tube. Regards.
@@RiftAmps Howdy again. Aha OK. PCB:s and tubes are issues waiting to happen. Thermal stress brakes traces or detach them from the board. PCB tube sockets are the worst. It is a pity. These days versatile amps have so much circuitry that turret boards are impossible. Regards again.
@@RiftAmpsThat's right. No sound or low sound. Right now I have two High End exotic amplifiers with the output transformers in shortcircuit, do you know someone who fixing it? It's very dificult because is single ended 845 tube amplifiers. Best Regards.
i killed the transformer in my Laney LC30 by putting vintage Mullards in it, not realising that they’re configured differently to modern EL84’s. 🤦♂️ New (better) Hammond transformer upgrade, big improvement.
Idk if this helps but, on the first amp you were looking at, a resistor in the power supply/output section looked a little crispy?
Howdy. If I understood correctly.
My DIY tube stereo PA does that. Signals go down as the power tubes heat up and start working. The neg. feedback kicks in lowering the driver signal levels. I never use global neg. feedback. I take the neg. fb. from the end tube anodes in my builds.
It seemed to me that the signal also got pointy when the end tubes began working. That would suggest biasing problems.
One might check the anode voltages without and with the end tubes inserted. If the voltage drops a lot it could be indicative of one end tube drawing much current. There might be red plating of the tube.
Regards.
Thansk for your message :)
If you watch the following video, the issue was a broken PCB trace on the PI feedback network. Interesting stuff!
@@RiftAmps Howdy again.
Aha OK. PCB:s and tubes are issues waiting to happen. Thermal stress brakes traces or detach them from the board. PCB tube sockets are the worst.
It is a pity. These days versatile amps have so much circuitry that turret boards are impossible.
Regards again.
Unless it's down to something with the camera, the second resistor along (next to the cream coloured one) looks rather cooked.
Just got a used Mesa jp2c
What are the most common symptoms of OT issues?
Most common? No output or v.low power
@@RiftAmpsThat's right.
No sound or low sound.
Right now I have two High End exotic amplifiers with the output transformers in shortcircuit, do you know someone who fixing it?
It's very dificult because is single ended 845 tube amplifiers.
Best Regards.
Thats a scary tidy wiring job. Jamie
i killed the transformer in my Laney LC30 by putting vintage Mullards in it, not realising that they’re configured differently to modern EL84’s. 🤦♂️ New (better) Hammond transformer upgrade, big improvement.
Yup, the VC30 also has that issue. Easily sorted with a quick socket rewire 👍
Output or power transformer? When you fried it did you just lose all power?