Tnx,

brian

kn4r

...

The UM-3s in the photo are East German (GDR) mobile amplifiers for low power man-pack FM transceivers. They put out 50 W, using the GU-50 tube. They're powered with a DC to DC power supply  (12 VDC primary and 750 VDC output); the older production used vibrators, the later were solid state inverters. The frequency coverage of the UM-3 is 21 to 46 MHz in 3 bands. The box labeled AW is a dual HF antenna tuner, one input for the R-104M transceiver (sort of mission equivalent to the GRC-9 and has a little more power but the frequency coverage is only 1.5 to 4.25 MHz) and the other is for the R-10. The AF is the antenna tuner for the R-108 (28 - 35.6 MHz low power FM man-pack transceiver). I also see 2 inverter supplies for the UM-3 (and possibly the R-104M).