04-14-2014, 12:25 AM
Have you done a complete recap? Most of the time that will fix problems like this, and even if it doesn't, you have to do it anyway. A good many of the paper caps are bound to be bad, and a few of the resistors, too.
Oh, yeah, and you have rubber coated wire all through your radio. Very likely much of it has turned brittle, cracked, and fell off the wires, leaving them bare. They really oughta be replaced or sleeved before putting power to it.
Tubes OK? If you don't have a tube tester at least test the continuity across the heater pins. It's probably not worth it to test for shorts manually, but keep it in mind for later.
I think given the symptoms I'd try to see if your oscillator is working. It's a pretty easy test.
Static from the speaker usually means the output Xformer is good, but I've heard noises from speakers even with an open primary.
Work back from the output tubes. Marcus and Levy recommend momentarily touching the control grid of the output tube with a plugged in soldering iron. You'll get a loud hum if all is well. Same with the control grid of the 1st audio amp section of your detector Amp tube. Also on the high side and wiper of the volume control. You can do this with the audio output of a signal generator, but the soldering iron method is quicker. Just be careful not to touch any of the high voltage connections.
After that you need a signal generator. Put 455 KHz modulated on the green wire from the 2nd IF transformer. If you get your AF modulated tone, do the same thing to the white/green wire from the 1st IF transformer.
Check continuity in both IF transformers with reference to the schematic. Remember that the brittle and cracked rubber wire is in the IF cans, too. There are also several caps and resistors inside the 2nd IF (33), so if you're not getting any audio from the from the modulated 455 KHz on the white/green, it's one of several things to suspect.
I'm hesitant to inject the 455 KHz modulated on the primary of the IF cans because of the high voltage, even with a cap between the sig gen and the IF primary.
If at any point working backward you stop getting positive test result, you've probably found the general location of the problem. Be sure your local oscillator works. That will zero the problem down more exactly.
Try those things and get back to us.
Oh, yeah, and you have rubber coated wire all through your radio. Very likely much of it has turned brittle, cracked, and fell off the wires, leaving them bare. They really oughta be replaced or sleeved before putting power to it.
Tubes OK? If you don't have a tube tester at least test the continuity across the heater pins. It's probably not worth it to test for shorts manually, but keep it in mind for later.
I think given the symptoms I'd try to see if your oscillator is working. It's a pretty easy test.
Static from the speaker usually means the output Xformer is good, but I've heard noises from speakers even with an open primary.
Work back from the output tubes. Marcus and Levy recommend momentarily touching the control grid of the output tube with a plugged in soldering iron. You'll get a loud hum if all is well. Same with the control grid of the 1st audio amp section of your detector Amp tube. Also on the high side and wiper of the volume control. You can do this with the audio output of a signal generator, but the soldering iron method is quicker. Just be careful not to touch any of the high voltage connections.
After that you need a signal generator. Put 455 KHz modulated on the green wire from the 2nd IF transformer. If you get your AF modulated tone, do the same thing to the white/green wire from the 1st IF transformer.
Check continuity in both IF transformers with reference to the schematic. Remember that the brittle and cracked rubber wire is in the IF cans, too. There are also several caps and resistors inside the 2nd IF (33), so if you're not getting any audio from the from the modulated 455 KHz on the white/green, it's one of several things to suspect.
I'm hesitant to inject the 455 KHz modulated on the primary of the IF cans because of the high voltage, even with a cap between the sig gen and the IF primary.
If at any point working backward you stop getting positive test result, you've probably found the general location of the problem. Be sure your local oscillator works. That will zero the problem down more exactly.
Try those things and get back to us.
John Honeycutt
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