The R-390 is a general coverage receiver introduced in the middle of the
fifties as the successor of the R-388, it has mainly been used by military
and official monitoring stations. In the manual, the set is described as
"general - purpose receiver for use in both fixed and mobile
applications" well suited for the reception of CW, AM and FSK signals,
with the R-390A itself, SSB reception is possible only with the use of the BFO,
there has been an optional external SSB adaptor with selectable sideband reception
available from Collins or alternatively the Technical Material Corp. CV-591A/URR.
The set has been developed by Collins but only a minority of all sets found on the
market are really "Made by Collins". Several contemporary manufacturers did
produce this receiver under contract (> see this) - the sets should match the same specifications,
it's said that not all the sets did...
The are two quite similar types of the R-390 receiver: the original 1950-1954 R-390
comes with LC filters, only the later R-390A comes with the legendary Collins mechanical
filters. The R-389 was a VLF variant, the R-391 features a motorized
frequency remote control and the R-392 was a compact receiver based on a similar
circuit but with 24V DC power supply for mobile use.
Using two R-390A receivers, You can use the space diversity technique to
eliminate selective fading effects on the reception: Two receivers on the
same frequency are fed from two different antennas and only the signal from
the receiver with the better signal level is switched to the headphones.
The receiver covers the range from 500 kHz to 32 MHz in 1 MHz segments,
You can read the exact frequency from a mechanical - digital "odometer"
type readout. The big rotary control "Megacycle Change" is used
for switching the correct MHz - segment, with the main tuning knob "Kilocycle
Change" You tune in the the correct Kilohertz setting in the range of
000 to 999, small 200 Hz interpolation lines give You an accuracy of better
then 100 Hz.
The main antenna connector of the R-390A is a Twinax type meant to conect
a (symmetrical) dipole antenna, it's signal has to pass through a tuned
preselector stage (tuning of this is coupled to the kHz / MHz controls by
many brass gears) before it's been handed over to the first RF amplifier.
Signals from the second asymmetrical connector, meant to connect to a much shorter
vertical antenna with lower signal levels, the signal will pass directly to
the first RF amplifier without having to pass the first tunes preselector stage.
At the same point, the signal of the internal crystal calibrator is coupled
in here. With an antenna relay, the antenna signal with be disconnected from
the first RF amplifier when the set is switched in break in and standby / calibration
In frequencies up to 8 MHz, the Collins R-390A uses triple conversion, in the
frequency ranges above 8 MHz double conversion circuitry.
In the frequencies between 0,5 - 8 MHz, the signal will be filtered and amplified
(the preselector circuits are tuned mechanically accordingly to the tuned frequency)
and will be mixed with a 17 MHz crystal signal to a first intermediate frequency
in the 17,5 - 25 MHz range.
In frequencies above 8 MHz, this step is bypassed and the signal will directly be
fed to the second mixer stage. In the stage, the signal is mixed with a crystal
controlled signal switched by the MHz control to achieve a second intermediate frequency
lying in the 2 - 3 MHz range. This IF will be mixed with the signal of the receiver
VFO: the axis of the permeability tuned frequency oscillator will be moved
coupled to the mechanical odometer - kilohertz - display by turning the big
kilocycle tuning knob. The perfect linearity and mechanical stability of the
permability tuned oscillator (PTO) made realisation of the mechanical digital
frequency display possible. To avoid frequency drift while the receiver is warming
up, the set is equipped with an oven switchable from the back of the receiver.
The PTO frequency can be varied from 3.455 - 2.455 kHz, so after the third
mixer a third IF of 455 kHz will be reached.
Ths IF will pass Quartz filters in the 0,1 and 1 kHz bandwidth positions,
in the other bandwidth positions, the signal will pass one of the famous
Collins mechanical filters in this place. Specially the 2 and 4 kHz IF filters
give perfect results in difficult reception conditions in the tropical bands.
After additional amplification in the 2. - 4. IF amplifier stages, the signal
is passed to the demodulator stage. The RF gain control will affect amplification
in the second stage directly. From the fourth IF amplification stage the AGC
level will be controlled, three different decay times are switchable.
The signal then is passed to the diode demodulator in AM mode, for CW reception,
a signal of 452 - 458 kHz from the beat frequency oscillator is added, so that
You will hear a beat note when receiving A1 signals. You can also use this for SSB
signal reception, when You regulate the RF gain carefully, You will get acceptable
results. Much better SSB reception is achieved using an external SSB demodulator
as the Tech. Material CV-591 or the Sherwood SE-3, the Collins made SSB demodulator
CV-157 is very scarce. There is also a switchable Noise limiter and a 800 Hz
audio filter for CW use.
From the diode demodulator, the AF signal is fed to an AF amplifier, the
"Local Gain" control will affect the signal level at the speaker
jack at the rear of the set. Caution: remember connecting a high impedance
600 Ohm speaker, use an AF output transformer if You plan to connect a modern low
impedance speaker. A second "Line Gain" control affects the audio
level on the "Line out" jack, this can be used to control a FSK converter
or an external power amplifier. The AF level is displayed by the meter in the
left upper corner of the front panel.
The other meter in the right upper corner marked "Carrier Level" will
display signal strength and has a 0 - 100 dB calibration, with 7,5 uV
the meter will show 20 dB and with 30 mV, it will reach the 100 dB line.
To achieve perfect frequency accuracy, You have to recalibrate the mechanical
frequency display after switching the MHz segment. The internal crystal calibrator
will give You a calibration signal avery 100 kHz, so tune the receiver to the
nearest 100 kHz point. Then disconnect the PTO from the mechanical counter
using the "Zero Adj" knob, this will act as a clutch when turned
clockwise. Use a IF bandwidth setting of 1 kHz, switch on BFO, BFO Pitch
set to 0 and tune to "Zero beat", this means turn the kHz control until
the whistling noise will become low pitched and will eventually disappear.
Then turn the "Zero Adj." knob counterclockwise to couple the PTO
to the mechanical display and You should end wit ha frequency display accuracy
of better then 200 Hz.
The crystal calibrator signals should give a S-meter deflection of 60 dB in
the lower frequency bands and of around 30 up to 35 dB in the higher frequency
ranges. Use the "Antenna Trim" control to adjust antenna coupling
to maximum S-meter / "Carrier Level" meter deflection.
This manoeuvre will give You a good impression whether Your Collins set is working
properly, useful when You consider buying one at a hamfest.
To operate the set turn the main "Function" switch to AGC position,
When You tune in the correct MHZ and kHz - digit with the "Megacycle Change"
and "Kilocycle Change" knobs, You can see all the marvellous gears
moving behind the front panel, it look like a clockwork - never take the mechanical
parts apart or try to reassemble the stuff as long as You are not a trained
watchmaker... Turn the "Kilocycle Change" until the desired frequency
is displayed, e.g. 6 - 1 - 5 - 5, You can lock the dial mechanically on that frequency.
Use the "Bandwidth" switch to select the IF filter appropriate for Your reception
conditions, the 16 kc filter gives You very crisp reproduction of the signal
if there is really no adjacent channel interference, I usually chose the 8 kc
setting for uncomplicated conditions and the 4 kc one, if there is adjacent channel
interference. This one and the 2 kc filter are responsible for the excellent selectivity
of the set in the tropical bands. The readibility of poor signals is surprising
everytime I use my Collins. Not that the Collins lacks the posibilities of
improving the readability by Passbandtuning and HF Notch filters as found on
modern amateur radio receivers quite often - but the IF filters help You a lot.
The audio quality is typical to the one of hollow state sets, no high pitch hiss
from the internal microprocessor, nor any "birdies" associated with computer
technology. To replace the missing Notch Filter, You might try an external Audio
Frequency Notch filter as the famous Dierking GD82 /GD84, for CW reception, the
R390A has an internal 800 Hz AF filter.
In practical use, I did compare my R390A quite often to my NRD-525 without
filter modification, a great set that is known as quite hissy and has suboptimal audio.
The signal strength of the private / christian broadcasters on higher frequencies
in the evening were similar on both sets, with the faint HCJB signals from
Ecuador, the 390 did a better job.
Just to check, what's on in a band, I prefer the '525 with it's direct frequency
input keypad, when I find good conditions, I like to turn on the Collins
and cruise the bands with it - as long as I don't have to overrun 1 MHz
segments, to go from 4980 to 5035 kHz is quite cumbersome, You will have to Switch
the MHz 1 higher and turn the kHz-dial all the way done - no problem, If You don't
plan to go back to 4980 for a second... That's why I prefer the '525 for checking
parallel frequencies - but the R390 for comfort listening of stations
with poor signals.
If You consider buying a used R390A, make sure You get a A-version with the
mechanical filters if You intend shortwave DXing. I prefer my Collins set,
usually the prices of the other contractors are a bit lower.
Of course, a set beeing serviced and realigned professionally by it's former
owner has a better value. I have given You a description how to check the
main functions using the internal crystal calibrator before. The mechanical
frequency readout and the gears should move without backlash and the frequency
display should be calibrated within the calibration range.
For all mechanical work on the set, You need only three tools: a Philips
screwdriver, a small spanner and - most important - a Bristo No.8 wrench.
If You're lucky, You find these tools still in place in a holder on the rear
of the set. Make sure that the previous owner hasn't spoilt the screws on
all the knobs using an ordinary Philips screwdriver instead og the Bristo
one, You might find a set so ruined so that You cannot even take away the front
Make sure to look out for the special antenna corrector.
Quite often, the meters are mising, as the radium coloured indicator give
a small amount of radiation, mane meters have been taken away, replaced or
You find sets with lead covers over the meter.
I found another problem: the voltage compensator of the set will "draw"
a small amount of current when the set is switched on: this will regularly
cause my RCD switch (Residual Current protective Device or Ground Fault Circuit
Interrupter (GFCI)) to switch off. As new houses in Switzerland
are equipped with RCD/GFCI security switches for the whole building or floor,
You might find it difficult to operate an R390 here. I think it's a wanted
operation of the compensator that will cause the protection switch to switch
off because it's happening on all my R390's, and I don't suspect all my R390's
to be faulty. A possible workaround is to use a "crossover transformator".