[Milsurplus] R-800 VHF set

[Jack Antonio]

A while back, I was fortunate to receive a complete R-800,
Russian VHF Radio. Even though I acquired a complete set,
including cables, it is by no means a matched set, the individual
pieces came from more than one aircraft. Most of the pieces
I have have Polish Lettering, with some Cyrillic lettering
thrown in as well.

It finally came up to the surface of the workbench, and I've
been spending the last couple weeks uncovering its secrets.

VK2DYM has a webpage showing pictures of the set, and an
excellent description, what follows are details I
have uncovered with this particular set.

My set appears to have been built around 1958, judging
by what looks like date codes on components. Based on
a paper tag on the receiver case, and some dates painted
on a couple of the tubes, it was last serviced around 1985.

With the exception of the inverter, and two of the four
control head connectors, all the interconnecting
cables use the same connector. It is an 8 pin
"Breeze" style external thread connector, looks
very similar to a U.S. Army PL-112. There is no
indexing, but each connector is marked with
the designation of the socket it belongs in.

The inverter is a single phase 115V 400 cycle unit, with
a carbon pile regulator. But it is not a standalone
unit, a portion of the regulator circuit is in the power supply.

The power supply is a straight forward unit, power
transformer with what I assume is a selenium bridge
rectifier. There is an additional smaller bridge to
supply bias.  Interesting circuit is a switch labeled
"PRZEL ZASILANIA" which connects the negative side
of the bridge rectifer to either ground or +28 volts.

Receiver. Uses equivalents to the 6AK5, 6SG7, 6H6, 6SQ7
and 6V6.  IF frequency is 12 Mc.  Crystal multiplication
is 18, except for frequencies around 120 Mc. At
those frequencies the crystal would be approximately 6 Mc,
and its second harmonic would fall in the IF. For those
frequencies the multiplier is 12, for a crystal frequency
around 9 MC. It appears from poking around with
the grid dipper, that the mixer is also doing duty
as a multiplier. One interesting fact is that the
IF cans are sealed, it would take considerable work
with a soldering iron to open them up.

Transmitter. No surprises here, 6V6 osc, 6V6 multiplier
832 multiplier, 832 final. Modulated by a pair of 6V6.
There is a 6AK5 used as a diode, to provide sidetone.
Total multiplication is 18.

Frequencies.  The frequency range of the set appears to be
100 to about 152 MC.  The dials on the selector mechanisms
range from 0 to 600, in increments of 120, but these are
not frequency indications, they correspond to channel code
numbers.  For example, channel 361 comes out as approximately
129.98.  This channel also shows up in the radios on VK2DYM's
page, so I'm guessing it is a guard channel. It is also
the only common channel between my transmitter and receiver.

Another quirk is that in the set I have, there is
no provision for turning the radio on or off, the
master relay in the inverter is wired permanently on
by the cabling. There is no power switch in the control head.

So far, I've breathed life into the receiver and transmitter.
The transmitter puts out 4 watts at a B+ of 250 Volts, the
limit of the bench supply. I found a crystal in the junque box
that put the receiver on Reno Approach, and it appears to work
OK. I have not powered up the inverter and power supply as yet,
all power coming from bench supplies.

Right now, the problem is figuring out the audio and keying
system. In the set I have, the PTT line would short out
the +28 volt source, and receive audio feeds the microphone
line through the 33K pot in the control head. This is probably
due to the fact that I'm looking at a mix-mash of pieces and
cabling from different aircraft with different wiring schemes.


More as I uncover it.

Jack Antonio WA7DIA
scr287 at sbcglobal.net