Sparton 75A
 

Here's a shot of the bottom of the chassis I was talking about. I have
discovered that the IF can lids come off easily, and that I CAN get to
almost every pin on the RF/IF tube sockets. Still no easy way to get to the
rectifier socket. Good thing I don't NEED to.

BTW.. I got the radio to play. It still needs a good calibration, and that
pretty much has to be done by trial and error until I can get a good service
manual for it. It has 6 bands, and all seem to be interlinked, so one
adjustment affects all bands.

The problem was a pot on the back of the chassis. It is an adjustment for
"interstation noise". It was open, but I actually had one in stock. It
varies the cathode voltages on all RF/IF tubes, and so the bias to those
tubes. Without the pot, there was 54 volts on the cathodes, so they were
biased off completely.