Well, I don't have much hair to begin with, so please help me before I pull out the rest
All caps replaced, tubes tested, ant coil checks good, band switch cleaned. AM works great but FM is completely silent. I did some voltage tests and the plates on V1 and V3 should be 95VDC. All I get is 72 volts. I get the same on AM and that works, so I'm lost.
Any ideas where to look next?
http://www.nostalgiaair.org/Resources/703/M0013703.htm
Thanks,
Hi Eric
How are the other B voltages?? The 120 and105?? If low replace the selenium rectifier with a 1N4007 or so. What I do is hook up an am signal generator to the ant and use a tracer to see where the signal ends.
Terry
Terry,
The rectifier has been replaced along with a 100 ohm 5W resistor in series. When I hook up my sig gen to the ant, it goes into V1 and doesn't come out. I replaced the tube with a known good one. Still nothing, not even static.
Thanks,
I'm not quite sure that I know what you mean when you say nothing comes out?? If you put a 100mc signal into the ant connect can hear it at pin 5 of the 12BA6?? Now you realize if you are using an AM generator set for 100mc your FM detector won't detect an AM signal. It's designed to detect a change in frequency not amplitude. That's why I said to use a signal tracer which will detect an AM signal.
Can you hear the signal from the generator at pin 5 of the 12BA6? In lieu of using a tracer you can use a scope but must have 100mc response or better. If you do then have a look at pin7 of the 12AT7. If not check voltages at 12BA6.
Terry
Your set contains three 12BA6 tubes my experience, the one used as FM-RF Amp if just a little bit weak Fm reception goes out the window. Try a simple swap and see what happens. Some Philcos from this time used a 12AU6 as the second IF Amp pin assigment the same as 12BA6. David
Terry,
My signal generator has died so the radio is going up on the shelf until I can replace it. I'll let you know when I get back to it. BTW, what I meant was that when I tried what you suggested, when my sig gen worked, I got no sound at pin 5 of V1, the 12BA6.
David,
I tried swapping tubes, no change. Not even static.
Thanks guys,
Sorry to hear your HP died nice piece of gear. As mentioned the 12BA6 is the RF amp for the FM only. AM has no RF amp. Double check the the plate, screen, and cathode voltages at the 12BA6. Also do you have 135vdc at the cathode of the rectifier and the junction of the input filter condenser to B-?( across the input condenser)
Terry