[Boatanchors] One Tube QSK Box (maybe called the "imp", Handbook, 1964)

[Freeberg, Scott (STP)]

Sounds like a tube TR switch like the Johnson TR switch.  While I never =
used one, but have one, I believe the transmitter is left in transmit =
mode all the time.  The TR switch detects rf and blocks rf from getting =
to the receiver and mutes it.  73, Scott WA9WFA