07-18-2009, 12:52 PM
Hi Bill,
Thanks for the help. All caps (except mica) have been replaced including the filters and buffer. The power transformer has been replaced in the past. I too generally gut 0Z4s and wire a pair of 1N4007s in the base but this time it checks out. I may still do it anyway. The socket looks clean but I will check for signs of arcing. Prior to the failure, plate voltages looked correct but I was having a heat-related problem where the audio would turn to static and then cut out after a couple minutes of operation like tube bias was going into cut-off. However, using the external power supply, the problem has mysteriously disappeared. I did manage to trace the problem back as far as the plate of the IF amp before the vibrator went south. Seemed like it was in the front end somewhere. I want to use a new solid state vibrator but don't want to cook it with excessive current. Guess I'm going to have to start lifting/testing all the resistors. I may try injecting AC into the transformer primary for a short duration.
Update: I momentarily powered the radio from the variac by applying about 15VAC into the vibrator socket and it worked fine. There are no carbon tracks or resistance or other apparent signs of arcing in the socket. I suspect the vibrator was just ready to die. A new solid state vibrator is now on order.
Thanks,
Ron
Thanks for the help. All caps (except mica) have been replaced including the filters and buffer. The power transformer has been replaced in the past. I too generally gut 0Z4s and wire a pair of 1N4007s in the base but this time it checks out. I may still do it anyway. The socket looks clean but I will check for signs of arcing. Prior to the failure, plate voltages looked correct but I was having a heat-related problem where the audio would turn to static and then cut out after a couple minutes of operation like tube bias was going into cut-off. However, using the external power supply, the problem has mysteriously disappeared. I did manage to trace the problem back as far as the plate of the IF amp before the vibrator went south. Seemed like it was in the front end somewhere. I want to use a new solid state vibrator but don't want to cook it with excessive current. Guess I'm going to have to start lifting/testing all the resistors. I may try injecting AC into the transformer primary for a short duration.
Update: I momentarily powered the radio from the variac by applying about 15VAC into the vibrator socket and it worked fine. There are no carbon tracks or resistance or other apparent signs of arcing in the socket. I suspect the vibrator was just ready to die. A new solid state vibrator is now on order.
Thanks,
Ron
