Well I have been cleaning up the bench, fired up my Z brand K731 that had always played well. No FM today.
It has been recapped and has played both bands well. Could not find a schematic at Nostalgia Air. 12DT8 possibly?
Any thought? I am much obliged.
Paul
Bandswitch always a sore spot appears to be fine, has been cleaned and is operating, maybe a tube.
Paul
Paul, I have a similar Z set the 12DT8 tube is a pain. I have had several NOS fail after maybe 50-100 hours went to using 12AT7, ECC81 which are current production. The BIG DIFFERENCE is pin 9 on the ECC81 is center tap to the heater, on 12DT8 pin 9 is internal shield to ground. One must remove the ground connection from pin 9 of the tube socket or kiss your new tube good bye in a flash.
Not a Zenith expert, but I have worked on one of these. I also had a problem with the FM, mine being a cut out and cut in problem. It turned out to be silver mica disease in the first FM IF. Unlike the same issue with AM, this SMD caused no thunder/crashing noises on FM (yours may be different).
I will try to attach a schematic (not sure it is the correct one, but it might help).
cheers
John
EDIT :: nope, I messed up the attachment ... gimme a minute ....
try this :
http://oldradio.ca/radio/Info/Zenith_K73...ematic.gif
I have one in my bedroom that the selenium rectifier was replaced by a diode and filter capacitors replaced. Also the electrostatic tweeter was replaced by a crystal tweeter. It still plays nice.
Rick Ethridge
Found mine at a flea market with a giveaway price as only the AM worked. Cosmetically it is near perfect. Started with the tubes and found 3 that were marginal/bad. Replaced those 3 and it worked perfectly (and still does today). Picks up lots of stations. Simplest fix I have come across yet! It was a while ago and I don't remember the tubes I replaced. Sure wish this model had a dial light.
Craig R