We have a vintage 251E with the original PSU. The mic had almost no output and seemed microphonic. I checked the voltage from the PSU (with the mic disconnected) and measured around 150 V (plate) and 0V (expected +4V for heater). I noticed a white wire that seemed to have broken free in the PSU. The wire connects to the bottom of the CT1104 power transistor and seems to have come off the terminal it is floating next to. I can't imagine why the lead came off unless it wasn't ever tacked on properly after some repair. I haven't found a schematic that resembles this PSU and before I tack this wire back on I wanted to see if anyone had any input on it. The mic was working fine during a session just last week.
thanks!
thanks!