[R-390] Russian HF Radios

Sat Aug 7 22:01:12 EDT 2004

The Russians indeed built a receiver in the same class and purpose as the
R-390 and R-390A. The frequency display was not the Veeder-Root
mechanical-digital counter as in the R-390* series, but an analog system
comprised of a coarse dial displaying each 2 MHz band  in 100 KHz increments
and a "fine" frequency dial which was projected from the rear, displaying
increments of  1 KHz, above the coarse dial. The receiver has  a dual
conversion system based on a tunable first IF of  1.5 to 3.5 MHz, mixed down
to  the 215 KHz fixed IF. The rest of the bands are converted with a crystal
oscillator/mixer to the variable IF, a la Collins. The difference is that
the bands are 2 MHz wide instead of the 1 MHz in the Collins system, and the
tuning is not a permeability tuning arrangement with slugs moving in and out
of the coils, but a multi-section main tuning capacitor and a drum
bandswitch system. The selectivity is infinitely adjustable (by variable
coupling of the 215 KHz IF stages, between 1 KHz and 14 KHz, and an audio
bandpass filter is provided as well, selectable between 8, 5, 2.5 and 0.3
KHz.
The receiver contains a thermostat-controlled ovenized crystal calibrator,
the BFO is tuned with a reduction drive, with a dial displaying   -5 KHz -
0 - +5 KHz frequency in  100 Hz increments. AGC time constants available are
1, 0.1 and 0.05 seconds or AGC OFF.
The RF input is selectable with a front panel switch  between a 60 to 400
ohm (nominal), balanced and unbalanced dipole, whip/long wire or ground,
antenna  trimmer control on the front panel.
There are jacks for AGC in/out for diversity, 1st and 2nd IF out, and 600
ohm audio line out (besides the headphone jacks).
The construction is modular: the RF/first IF/crystal oscillator/mixer is in
the bottom drawer in the cabinet, the top drawer contains the second IF,
BFO, AGC, detector and audio circuits, as well as the metering circuit - the
receiver has a built-in emission tester and each tube can be selected for
test while the receiver is in operation, or the meter can be switched by the
selector to monitor the audio line output or the received signal strength.
The power supply is external, and interestingly the input is selectable
between 220 and 120 VAC...

The first version of this receiver was put in service with the (former)
Soviet Armed Forces in 1948 with the military nomenclature of R-250
("Whale"), and the improved version, the R-250M was issued in the early
1950's. Both these models used standard metal octal tube types, which are
equivalent to the US types. In the early 60's the receiver was modernized
and standard miniature tubes were used together with some circuit
improvements. The self testing arrangement got an additional feature, a
built-in noise generator, so besides emission testing of the tubes, a
sensitivity check could be performed without external test equipment (like:
"Hey, Sergey, I can't copy headquarters!"  "Check the receiver with the
noise generator, Ivan!" "click, click, click as the meter switch is turned
to check each tube, and the input with the noise generator"- "There is
nothing wrong with the receiver"  "S**t! The ice broke the antenna again!")
This version was the R-250M2 and was in production until 1981.

Incidentally, in all these receivers the B+ is 160 VDC, giving the tubes a
real long and cool life, with a total current draw  of 120 mA!  The
filaments are series-parallel connected (all 6.3 V tubes) for 12.6 V at 6 A.

I own a pristine R-250M model. Its performance is simply incredible,
considering an early 50's design with all octal tubes (19 of them). It
outperforms many receivers 10 years more advanced. The spec on the
sensitivity is 0.6 uV  for S/N ratio of 10 dB at 3 KHz IF and 2.5 KHz AF
bandwidth, with a 100 ohm antenna. Audio output is 0.5 W into 600 ohms at 4%
(AF output tube is a Russian 6P6, which is the exact equivalent of the 6V6).
Frequency stability is specified as maximum 200 Hz drift after a warm-up of
2 hours!
The tube complement in US equivalent designations is  10 x 6SK7, 3 x 6AC7,
3 x 6SA7, 2 x 6H6, 1 x 6V6, + a voltage regulator tube (I have to find the
US equivalent) and the power supply has a 5Z4 rectifier.
The detector/BFO injection is good enough for good SSB reception, even with
the AGC on, as well as CW is just great to copy on it with all the
selectivity options.
It's no slouch in AM quality, although  .5 W  is really not enough to drive
a big speaker without an outboard amp.

All this in a real "boatanchor" package of 26" wide, 18" deep and 21" tall
(with the shock mounts), weighing 209 pounds, without the power supply,
which weighs about 35 pounds.
Options available were RTTY demodulator, high precision AFC (Automatic
Frequency Control) system, which provides tuning with a servo motor and a
diversity control interface. There was also a vibrator power supply option,
for 12 VDC input.

Construction is really excellent quality and it looks like good US mil-spec
work. The wiring and soldering are also first-class, the components look
high quality. The transformers are potted, cased and painted, just like the
US mil. stuff. Incidentally, I got a couple of sets of NOS spare tubes, with
1972 manufacturing date. Pretty late for still making metal octal military
tubes!

There are photos of the various versions at a Russian web site
http://www.cqham.ru/trx/r_250.html .

Well, I hope this wasn't boring, but there is not too much traffic here
tonight anyway...

73, Meir WF2U
Gowensville, SC

 -----Original Message-----
From: 	r-390-bounces at mailman.qth.net [mailto:r-390-bounces at mailman.qth.net]
On Behalf Of Bob Camp
Sent:	Saturday, August 07, 2004 5:15 PM
To:	Cecil Acuff; R-390 HF Receiver List
Subject:	[R-390] Russian HF Radios

Hi

Well obviously we need to get something going.

How about did the Russians build a better all tube HF receiver than the
R-390A? From what I hear the answer may be yes ....

That's the way to see if anybody's listening.

	Enjoy!

		Bob Camp
		KB8TQ

On Aug 7, 2004, at 4:57 PM, Cecil Acuff wrote:

> Test...
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