1970 Marshall JMP 50 watt

[Dale]

hey you guys I just picked up a 1970 50 watt for cheap that appears to be stock except for the Hammond replacement transformers. When I plugged my Bias King in the power tube closest to the PI had no current running thru it. Im a little dumb when it comes to amplifiers but would really appreciate any suggestions, Im sure this amp sounds good. I also dont know how to up pictures on here Thanks

[danman]

Does the amp play ok or have you heard it play? How about the other power tube socket...are you reading any current there? If the amp plays fine and your tubes are not redplating then I would guess a bad bias meter. Are these a fresh set of tubes that you know for sure are good?

[danman]

I meant to mention that the old 50 watt Marshalls had an issue with their bias wiring that caused alot of power transformers to burn up in these amps back in the day. That may be the reason yours has the Hammonds in it now. It's a simple matter of moving one wire to fix this issue but we would need to see some pics of the board to determine if it's needed. This would not cause the issue that you are having right now so first you need to find out why your not reading any idle current.