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PT-25 Pilot Lamp keeps burning out?
#2

Check that resistor which is across the pilot light. My bet is it opened up. That would be the 33 ohm section of R29. If it is the metal cased resistor that is not surprising. That is a Candohm resistor, and they do fail. Ring it back from the bulb socket and you should find one side going to one end of R29, and the other side going to the middle terminal of R29, and the resistance of R29, with the bulb removed, should read infinite, or very high if that section is bad, if it is good it should read about 33 ohms. The other section should read about 175 ohms. If a section is open, one can solder an appropriate resistor in place of the bad section. The current the resistor will see, max, would be about 0.15 amps, so 0.15 x .015 x 33 = 0.7425, you will need a 33 ohm resistor, 1 watts MINIMUM, 3 is better, to replace that section of R29 Just remember, the bulb will also be taking some of that 0.15 amps, so not all of it will be going through that resistance usually. That resistor is there to keep the radio playing when the bulb burns out, but the bulb should always be replaced as soon as possible to prevent strain on the resistor. Unfortunately the schematic does not list the bulb type, and the parts list only gives a Philco part number, but I am sure Ron, or one of the others here, more familiar with these radios than I, can tell you what the actual bulb type should be. Based on the voltage the 33 ohm resistor would see WITHOUT the bulb, about 5 volts, my guess is it is a type 47. I'm sure you can figure it out.


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RE: PT-25 Pilot Lamp keeps burning out? - by mikethedruid - 02-09-2021, 12:52 AM



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