[Boatanchors] Collins R 390 and an R 391 sets

[Dan Arney]

Bill,
They are the same receiver with the exception that the R-391 has auto 
tune capability to be remotely tuned. They were paired in the FRR/33 
RTTY diversity system. The R-391 requires a separate 28 VDC power supply 
  for the autotune system. If look close at the MC/KC knobs you will see 
a wing nut in the center, that is unlock the autotune knob to set the 
frequency for one of the 8 channels. It also has a channel selector knob 
under the bandwidth and a remote local knob under the left side of the 
freq. dial. It can be manually tuned like the R-390 by unlocking the 
autotune lock pins, but no fun.
I have the complete FRR/33 setup with rack mount and desk top remotes 
which is the way it was designed to be operated.
73
Hank
KN6DI