09-13-2015, 02:17 PM
Great advice. I'll look in my Marcus and Levy right away. I'm pretty comfortable with the switch, now. It makes no changes to the original circuit and its switching simply places the RCA jack in the circuit or shuts it out. I am keeping it out of the circuit while I troubleshoot the rest of the radio.
I've got the signal generator on it, now, and I'm able to get a strong audio tone from the top of the volume pot, so the output seems OK. I've measured all three IF transformers and have measurements similar to the schematic (3rd IF was difficult; I had to remove the push button electronics and got a good measurement on its primary winding, but couldn't figure out how to get the secondary, so I measured it AFTER the two resistors and got a number close to the added resistance of the winding plus the two resistors). The antenna coil and the oscillator coil measure good on all windings.
I can hear a modulated tone at 455KC from the plate and grid of the 1st detector, and from the plate of the oscillator, but get nothing from the oscillator grid which isn't surprising after I measured the voltages at the plate and grid of the oscillator. The plate was 10vdc and the grid was less than -1vdc (should be 40vdc on the plate--I can't find a suggested grid voltage, but should be about -8 according to Radio Museum).
I have to wait until tomorrow to look at it again, but I thought I might trace the filaments' voltages down the line, and look at what happens from C27 through to the plate of the XXL oscillator. I hope I don't end up replacing several mica caps around the band switch. Any suggestions would be appreciated.
I've got the signal generator on it, now, and I'm able to get a strong audio tone from the top of the volume pot, so the output seems OK. I've measured all three IF transformers and have measurements similar to the schematic (3rd IF was difficult; I had to remove the push button electronics and got a good measurement on its primary winding, but couldn't figure out how to get the secondary, so I measured it AFTER the two resistors and got a number close to the added resistance of the winding plus the two resistors). The antenna coil and the oscillator coil measure good on all windings.
I can hear a modulated tone at 455KC from the plate and grid of the 1st detector, and from the plate of the oscillator, but get nothing from the oscillator grid which isn't surprising after I measured the voltages at the plate and grid of the oscillator. The plate was 10vdc and the grid was less than -1vdc (should be 40vdc on the plate--I can't find a suggested grid voltage, but should be about -8 according to Radio Museum).
I have to wait until tomorrow to look at it again, but I thought I might trace the filaments' voltages down the line, and look at what happens from C27 through to the plate of the XXL oscillator. I hope I don't end up replacing several mica caps around the band switch. Any suggestions would be appreciated.
Charlie in San Antonio
