On Apr 8, 3:20 pm, (Gary R.) wrote:
... is it a function of this early radio that it has no
sidetone---or a wiring problem?

I have flown older Cessnas that had the 300 series NavComs, and they
had sidetone.
Sidetone is generated inside the COM by sampling the audio from the
transmitter modulator
and routing it out through the "headphone" output pin, so you should
hear it when you transmit.
Either the radio has an internal problem, or possibly the "sidetone
level adjust" pot got turned down.
Most COMs have a "sidetone level adjustment", usually visible only
when the radio is out of its tray...