[Milsurplus] Tube radio Product detectors

[Greg Mijal]

Hi:

I was thinking about something I see here at the repair bench.  Some of the receivers and transceivers I work on have something funny going on in the product detector.  Turn the radio on, let it warm up and no audio.  Rock the mode switch to SSB and poof! rig is now receiving normally and stays that way for whole time it is used.
What causes this?  Even my 75S1 does it and now I have a Galaxy transceiver with the exact same symptom.
What's up?
Tnx
Greg
WA7LYO
Kinston NC