[R-390] The infamous squelch non-option

[Tim Shoppa]

I've been able to figure out that the empty filler plate on a R-390A's audio
deck is for some sort of squelch option. As I get more receivers accumulating
around the shack, I'm starting to appreciate how squelch could make sense
in a lot of environments.

The blank plate covers the mounting holes for a tube socket and a relay, right?
What other componentry had to be added? I see the non-terminated wiring
harness near that spot, anyone have a schematic diagram of what might go there?

I probably will try to rig up some sort of squelch system, and probably outside
the various receivers. In particular what I want to do is be able to monitor a couple
of HF utility frequencies and have them break in over SWL broadcasts when there's
something happening, this is more of a prioritizing rather than a simple squelch
scheme. Still, I'd like to see how they thought it would be done in the R-390A.

Tim.