July 21, 2018 at 10:04 pm #10292KyleForum Participant
I have restored a Westinghouse 99. Replaced all caps (except mica) and wiring a year ago. Since then I’ve been fighting with it. The resistor on the power supply unit seems to be overloading/over heating. It’s the 7k ohm resistor between pins 3 & 4 in the schematic. I’ve checked my circuits over and over. Disconnected circuits to eleminate them. Any ideas?
Attachments:July 31, 2018 at 1:59 pm #10332philForum Participant
Kyle there are others who may be able to advise better with more bench experience.
but check the power supply to see if the tar is melting out or anything. You might take a measurement across the plug and across the windings. maybe you could check if the primary and secondary are isolated and what the resistance through each coil is.
if you post that info then maybe someone here could make sense of your readings to tell if it was within a reasonable range.
It could happen that the transformer got hot and if the windings are shorted part way through the coil it could possibly result in a shorter coil with lower resistance. If you have access to another set then maybe you could measure it and draw comparisons. If you recapped it make sure you did not install any electrolytics backwards as polarity is important. Maybe its old enough that the power supply had non polarized caps. later radios had electrolytics but on some of the early ones they just used paper caps even though they may be in a tin box potted in tar.
here is an article about a guy restoring a westinghouse columair with a bad power supply and I though maybe some of his notes might make more sense of it than I can 😉
i spoke to one collector who was restoring a columair and he found one tube with an internal short. He figured it was because the tube wasn’t meant to be installed horizantally like it is in the columair. maybe you could check the tube pinouts with a meter and the tube removed just to see if that could be the case?
August 2, 2018 at 5:14 pm #10337John GreenlandCVRS Member
- This reply was modified 4 years ago by phil.
In looking at the full schematic, it seems that the 7Kohm resistor is used in the cathode circuits of some of the tubes.
According to the voltage chart and taking into account the 2 voltages for terminals 3 and 4 one should be able to assume a voltage of about 130 volts across the 7000 ohm resistor.
This much voltage drop will necessitate a 2.5 watt resistor (minimum from calculations).
I would suggest that if the resistor that you have is large enough power wise and the value is OK, but the voltage across it is more than 130 volts or so, then a possible problem might be a shorted cathode to heater in one of the tubes causing an extra current draw thru the 7000 ohm resistor. More current will mean a higher voltage drop and a more heat.
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