Rebuilding the R-390A Receivers
Brief History - Assessing your Receiver - Disassembly
The Main Frame - The RF Module - The IF Module
The AF Module - The Power Supply Module - The PTO
Restoration - Alignment -
| PART 1
- History, Assessing your Receiver, Main Frame, RF Module, IF Module,
Audio Module, Power Supply, PTO
PART 2 - Front Panel Restoration, Other Details, Contractors List, Receiver Alignment, Expected Performance
PART 3 - Misc Info on R-390A, Restorations 1967 EAC, another 1967 EAC, Arvin R-725, R-390A Diversity Operation
PART 4 - Dynamotor R-648/ARR-41, R-389 Restoration, R-392 Info, Other R-390 Variants, Dial Cover, CV-979 Cabinet
Front Panel Restoration
Silk-screened Panels - All Collins and Motorola R-390A receivers use front panels that have silk-screened nomenclature. This presents a problem if the panel is in rough condition. About the only solution is to look for a decent condition replacement panel. If originality isn't an issue, a silk-screened panel can be replaced with an engraved panel. Be aware though, that Collins and all of the other contractors used a short serial number tag with the exception of Motorola. The Motorola contracts used a 3" long tag with different locations for the mounting holes. If you're trying to maintain originality with a Motorola contract R-390A, then you're going to have to find another Motorola front panel. (Note: Early contract Collins R-390A receivers also use the long 3" data tag.)
Engraved Panels - Repainting an engraved front panel is very easy. Be sure to mask the back of the panel (if you're going to paint it) where the panel mounts to the Main Frame and also a small area by the upper left mounting screw for the Carrier Level meter. Some panels will have nomenclature on the back that identifies some of the components. These are usually the earlier silk-screened front panels as later engraved ones have nothing on the back but the paint. Be sure to use automotive grade paint that is purchased from an automotive paint dealer. This type of paint will have special hardeners that make the paint really durable. Also, professional paint will dry "ultra-thin, hard and flat" which will help make filling the engraving a lot easier. After painting, let the panel dry at least overnight before doing the engraving fill.
End-user Panel Repaints - The R-390A specifications state that the front panel is to painted medium gray. The manuals give a specific part number for the paint but it seems the shade of gray did change over the years from contractor to contractor. When choosing the color for repaint, try to get as close as you can to your receiver's original panel color by having the original paint matched at an professional automotive paint supplier. Only use automotive quality paint for repainting the front panel. Nearly all R-390A panels are found painted gray, however, sometimes the end-users did repaint the front panels totally non-specification colors. The USAF had banks of R-390A receivers at Clark AFB in the Philippines that were painted flat black (actually, black anodized finish.) Once and a while, olive drab panels turn up, supposedly painted that way by the USMC. At any rate, there is some evidence that R-390As were painted colors other than gray when the end-users had some reason to do so. Remember, all R-390A receivers left the contractor's facility with gray panels (and that's original) but it can be considered "acceptable" to paint the R-390A panels colors other than gray if there is believable evidence that the color was actually used on a receiver that was operating in a commercial or military capacity.
Engraving Fill - I use Artist's Acrylic paint to match the engraving fill paint. If you use pure white it will look way too bright. You should mix a color that is close to that found on manila folders - kind of beige color. Apply the fill paint to one part of the panel nomenclature at a time. Use a small paint brush and dab the paint into the engraving. Don't try to just paint into the engraving - you have to dab the paint into the engraving to have enough there and, of course, you'll have some paint around the engraving - that's normal. Let the fill paint set for about one minute. You'll now have to remove the excess paint around the area. Use a rubber squeegee to remove the excess paint. Be sure to wipe the paint off the squeegee each time you make a pass to remove the excess paint. Next, use a damp paper towel folded very flat to remove the small bit of remaining paint on the panel. You'll have to be careful not to "pull" the fill paint out of the engraved area, so keep the paper towel pieces small and only use them once. You'll have to have several damp paper towel pieces ready as you do each area on the front panel. Also, I've found that if you dampen the paper towel pieces using Glass Plus instead of water the Artist's Acrylic comes off much cleaner. These paper towel pieces should be just damp - not wet! When finished let the panel dry overnight. The next day you can apply carnauba wax to protect the panel and the engraving fill which will enhance the overall panel appearance.
IMPORTANT NOTE: Don't use Windex to dampen the paper towel pieces. Windex contains ammonia which might damage the new panel paint. Glass Plus doesn't contain ammonia but works very well to remove the excess paint without damaging the panel paint.
The Back of the Front Panel - The backside of the front panel has several clamps for holding the harness in place. Also, there is a printed circuit board mounted on the back of the front panel just above the frequency readout bezel. There is a lot of mechanical stress on the various wires when the front panel is lowered so check all of the wires to the pots and switches for any breaks or other problems. Since you have removed the front panel for repainting (or replacement,) then you'll be remounting all of the pots and switches along with the phone jack, dial lock and the zero adjuster. Note also that there is a grounding lug on the upper left (as seen from the front) stud of the CARRIER LEVEL meter. This provides a chassis connection for one of the AGC delay capacitors.
Use the Correct Lock Washers - Each nut that secures a potentiometer or switch should have a internal tooth lock washer installed. There are five 6-32 flat head phillips screws that mount into the Main Frame bed and into one of the vertical dividers (into pem-nuts) on the underside of the bed. These screws each have a #6 conical external tooth lock washer installed. If you're missing the conical lock washers, they are available from McMaster-Carr (boxes of 100 - they're cheap.) Notice that the three 6-32 flat head phillips head screws that mount the cable clamps have split ring washers mounted on the back side of the clamps (along with nuts.) The eight 10-32 flat-head screws that mount the panel to the main frame vertically will thread into Nylock pem-nuts, so no lock washers are required.
Mounting the Front Panel to the Main Frame - When mounting the front panel, note that the Dial Lock has to fit over the KC tuning shaft lock-plate. Leave the Dial Lock loosely mounted so it can be rotated to clear the lock-plate. Once the front panel is mounted, you can rotate the Dial Lock into position (the locking grips on each side of the locking plate with the locating tab in the hole one the backside of the front panel) and tighten the mounting nut. >>>
>>> If you have the two large shaft bushings (KC and MC Tuning) and the three small shaft bushings mounted to the front panel you'll find it difficult to guide the shafts thru the bushings because of the harness length. Although you could dismount the harness clamps, it's easier to just plan ahead and slide the rear panel shaft bushing onto the shafts and then mount the front panel to the Main Frame. You'll find with the large openings, it's really easy to guide the front panel over the shafts with the harness clamps tightly mounted. Once the front panel is mounted, then slide the rear bushing forward and slide on the washer and thread on the front bushing.
Once everything is mounted to the front panel and the front panel is fully mounted to the Main Frame (and tightened,) then you can go ahead and adjust the panel shaft bushings for the best feel when rotating the controls.
Front Panel Bearing Adjustment - If you want your R-390A to tune "light and easy" then you're going to have to adjust the front panel feed-thru bearings. These are on the KILOCYCLE and MEGACYCLE tuning shafts.
After a thorough cleaning of the RF module gear box, you probably noticed that the KILOCYCLE tuning was very light and easy to manipulate. As you reinstalled the slug racks, the tuning became slightly more difficult to manipulate but was still very light and easy. When the front panel was installed, all of a sudden the tuning seemed to drag and was noticeably more difficult to manipulate. This is caused by the two panel feed-thru bearings. When the RF module is removed and then reinstalled, it's very slightly, differently oriented and the same goes for the front panel. Only a slight misalignment of the panel bearings will cause a "heavy-feel" to the tuning.
Before the front panel is reinstalled, slide the rear bushing onto each shaft. Fit the front panel into position over the shafts and begin installing the mounting screws. With all of the screws tightened that secure the RF module to the Main Frame and all of the screws tightened that secure the front panel, then slide the rear bushings forward and mount the washer and front bushing nut. Note how the bearings can be moved within the feed-thru mounting hole. This is to allow proper placement of the bushing to act as a guide and bearing for each shaft.
Using a 5/8"open-end wrench, lightly tighten the KILOCYCLE bearing nut being careful to not move the position of the bearing itself. Then try the KILOCYCLE tuning. If the tuning is very light then try to just slightly tighten the bearing a bit more - not too much - the bearings don't have to be mounted "super-tight." If the tuning is still light then the adjustment is fine. Usually, no matter how the bearing is adjusted, there will be a slight increase in the "drag" because of the bearing itself. The adjustment is to achieve the lightest "feel" while still providing support for the shafts.
Do the same procedure for the MEGACYCLE tuning although this tuning is much more difficult anyway since you're moving so many of the slug-racks and there's also a detent about every turn of the shaft. Adjust this bearing for the best "feel." You can also apply a drop of machine oil on the shafts to help lubricate the oil-lite bronze bearing that is inside each of the feed-thru bearings.
The end result will be a KILOCYCLE tuning that is very easy to manipulate and feels great when fine tuning is required.
The three small (.25" shaft) bushings are adjusted in the same manner (ANT TRIM, BANDWIDTH, BFO.)
Meter and Line Level Meter - If an R-390A receiver has
been obtained from either a surplus source or other "official-type"
dealer, both meters may have been removed. There was (is) a concern that
the radium-coated scale and needle leaked too much radiation and that
was a cause for meter removal and "proper" disposal. Whether or not the
radiation level is anything to be concerned about is up to the
individual user/owner but that's why many meters are missing from the
R-390A receivers. NOTE: Most (all?) R-390, R-391 and R-389 meters
don't have the radium coating on their scales or needles.
When proper replacement meters are found they will likely be in "rough" condition. It's easy to mask the glass and give the body a light coat of flat black paint. If there are heavy scratches or gouges, these will have to be removed with either a file or Al-Ox paper followed by a paint job. I've also "touched up" the meter cases and then used 0000 steel wool applied "lightly" to even out the finish. Be sure to use the gaskets (if you have them) between the meter body and the front panel.
If you want to get inside one of these meters it is a difficult operation that usually ends up ruining the meter. Proper tools are necessary and one should always where protective gloves. Avoid opening the meters if at all possible. If you are contemplating changing the scales to something non-radioactive, this would probably create more of a "radiation problem" than to just leave the meter "sealed." Besides, you still have the radium-coated meter needle to deal with. Most user/owners feel that the meters are safe when used properly. In other words, don't eat the needle, don't tape the meter to your chest and leave it there for a year or other things that normal users wouldn't do anyway. At a distance of three inches the meter's radiation leakage is not even measurable. That's because it is a "sealed" meter.
- These are made out of stainless steel and can be easily cleaned up
with 0000 steel wool and a small brass brush for the washers and the
flanges. Wash with Glass Plus before installing.
Dial Cover - This cover, unfortunately, takes a lot of "hits" and as a result is sometimes found dented, scratched or both. Inside the cover is painted with zinc-chromate primer which is bright yellow-green color. Usually the inside is okay but if the cover has dents to be removed, it might need repainting after the body work is finished. Outside the cover is semi-gloss black. Automotive-quality paint should be used for painting the exterior of the cover.
Knobs - The knobs also take a beating and many times will need to be restored. First strip the old paint off with a methylene-chloride type stripper. Go over the knobs with a wire brush afterwards. Use a high quality automotive paint in semi-gloss black. Let the paint set overnight. Mix "manila" Artist's Acrylic as described above for front panel nomenclature fill and use the same procedure to add the index line for the knobs. Let this set up for a day and then give the knobs a coat of carnuba wax and install.
The Contractor Companies, Contract Numbers and Build-Years for R-390 & R-390A Receivers
1951 - Collins Radio Co. - contract 14214-PH-51 (contract 14214-PH-51 was also used for R-389, R-391 and early R-390A receivers)
1952 - Motorola - contract 26579-PH-52
1954, 1955 - Collins Radio Co. - contracts 375-PH-54 or 08719-PH-55 (early R-390As built on 14214-PH-51 contract)
1955, 1956, 1958 - Motorola - contracts 63-PH-54, 14-PH-56, 14385-PH-58
1959, 1960 - Stewart-Warner - contracts 42428-PC-59, 20139-PC-60-A1-51
1960 - Electronic Assistance Corp. - contract 23137-PC-60 (may have been for modules only)
1961 - Capehart Corp. - contract 21582-PC-61
1962 - Amelco - contract 35064-PC-62
1963 - Teledyne-Imperial - contract 37856-PC-63
1963 - Stewart-Warner - contract DA-36-039-SC-81547
1966 - Communications Systems - contract FR-11-022-C-4-26418 (may have been for modules only)
1967 - Electronic Assistance Corp. - contract FR-36-039-N-6-00189
NOTES: The first few hundred R-390A receivers built by Collins will have long data tags with 14214-PH-51 contract number. Remaining Collins receivers have short data plate with either 375-PH-54 or 08719-PH-55 contract numbers. Amelco was supposedly an alternate name used by Teledyne. Electronic Assistance Corporation was owned by the same conglomerate that owned Hammarlund in the sixties. It's often reported that Hammarlund owned EAC but the "Hammarlund Connection" for EAC is vague at best.
|Ovens - Crystal Oscillator, PTO, Cal. Crystal - There really isn't a need to have these ovens operating. Maybe it was necessary when the receivers were operated by the military but today's amateur operations don't require that degree of frequency stability and the operation of the ovens increases the heat within the receiver substantially. To turn off the all ovens, look for the switch on the lower right corner of the rear panel. It's marked "ON" and "OFF" and to switch off just align the screwdriver slot of the switch to be inline with "OFF." It's surprising how many R-390s and R-390As will be found with the ovens still operating. It's not necessary and just creates more heat and consumes power unnecessarily.||A Note on All-Matching Modules - This is generally an indicator that the receiver has not been used extensively and has not gone through any sort of echelon rebuild. These types of receivers are desirable in one sense since they usually haven't been brutalized by careless technicians. Most enthusiasts consider the "non-matching modules" equipped R-390A to be inferior since it has obviously been worked on in the past. If you intend to use an R-390A "as delivered" then the all-matching modules type gives you a chance this "out-of -the-box" operation might be possible. However, if you intend to rebuild the R-390A before putting it into operation, then the "non-matching modules" type will be a more reasonably priced option. All of the modules are basically the same regardless of which contactor built them. There are minor differences but they are all interchangeable. You will find that the early Collins and Motorola IF modules don't have adjustments on the inputs and outputs of of the mechanical filters unless they've been upgraded. The ECO was issued in mid-1956. It might seem that the early Motorola RF transformers are of a higher quality than the later EAC units (that used American Transformer units.) However, in early RF transformers it's common to find a stuck rotor and stator on the trimmers. This isn't usually found on the later-manufactured RF transformers. These minor issues are just an evolution of production methods. The contactors had to meet a detailed specification when building each module and all modules will perform to spec after a rebuild. Certainly, if you enjoy the rebuilding process, then a "non-matching modules" R-390A will be your most economical route and you won't have to be concerned about disturbing the unit's originality. However, now at 50 years old, even the all-matching 1967 EAC R-390A receivers should be thoroughly checked over before operating.|
The Receiver Alignment
Power-up after Rebuild You should have the R-390A
receiving stations on all bands with power on. You can turn on the CAL
and the BFO. Then tune to a 100kc calibration signal. Now rotate the MC
knob through each of the bands listening for the calibration signal.
Normally, you'll hear the CAL signal on every band although it will be
at various tone-frequencies depending on each band's particular
alignment at this time. You should hear the signal on every band though.
This will assure you that everything is basically working and the
receiver is responding to an input signal on each tuning range.
Things to do Before Proceeding to the Fixed-IF, Variable-IF and RF Alignments - you should first do your PTO end-point error correction, if necessary (it will be.) Be sure that the Calibration Oscillator is set correctly and the Veeder-Root counter is in sync with the PTO (you should have checked both before doing the EPE adjustment.) Also, check the Crystal Oscillator output at E-210 and be sure the voltage there is between -3.5vdc and -8.0vdc on the 8mc to 31mc tuning ranges. The voltage should appear when the MEGACYCLE knob is on its detent for each band. You don't have to check the .5mc to 7mc bands because these crystals and associated oscillator circuits are both fundamentally and harmonically operated and also work in either a double or triple conversion scheme. They were actually checked in the higher ranges. Be sure your DIAL ZERO is mechanically centered within its approximately one-sixth turn of the KILOCYCLE tuning when calibrated to XX.000 on the Veeder-Root counter.
Error in Army TM 11-5820-358-35 - Field Depot and Maintenance Manual for the R-390A from December 1961. Alignment instructions, page 116, paragraph 76b (2) indicates that URM-25 Signal Generator should be tuned to 18.75mc. Actually, the correct frequency is 18.25mc. This error was very obvious to technicians doing the alignment and is very well known. Interestingly, the earlier TM 11-856A Technical Manual for the R-390A has the correct 18.25mc information, so this later error was probably a typo that wasn't caught in proof-reading.
How to do the Balanced Input Alignment - Make up a test resistance that consists of two 68 ohm 1/2 watt carbon resistors in series. Each separate leg of the resistors will push into to each terminal of the Balanced Input Twin-ax connector. The junction of the resistors will be connected to the signal generator. When performing the alignment of the RF stages first adjust the Balance trimmer on the the RF transformer for the minimum voltage on the DIODE LOAD as read on an (analog) VTVM. The Balance adjustment will not reduce the DIODE LOAD voltage to zero - you're setting the Balance trimmer for the minimum voltage. Be sure the ANT TRIM is set to 0. With the minimum voltage set, now proceed with the RF adjustments for that section of the receiver. Recheck the Balance trimmer adjustment after the particular RF section has been aligned. The Balance should still be close but will probably need just a slight adjustment for minimum voltage at the DIODE LOAD. Recheck the RF alignments - but there should be no significant change and just a slight "tweak" should be all that's required.
|Does it Really Matter -
Balanced or Unbalanced Input? - If you do the Balanced
Input alignment, then the answer is yes. Correctly aligned you might see
an improvement if you are using an adapter that grounds one side of the
two terminals and connects an unbalanced antenna (that is matched for
the received frequency) to the other terminal. This method runs the
signal through a set of tuned coils before going to the RF amplifier
stage. If you haven't performed the balanced alignment then it's very
possible that a reduced signal level may be experienced with this method
of connecting the antenna. In this case, connect your antenna to the
Unbalanced input (but, eventually, you'll want to do the Balanced Input
alignment.) Originally, the Balanced Input was for dipole antennas that
used a balanced feed line in the 100 Z ohm range utilizing the "twin-ax"
type coaxial cable. Nowadays, hardly anyone runs a balanced antenna
directly since most transmitters operate into unbalanced loads.
Additionally, the "twin-ax" type cable has a significant db loss per
foot. If you're using a tuned antenna with antenna coupler, you might
find that the Unbalanced input works better. This may also be the case
if you're using a vertical antenna directly fed with coax. Go ahead and
do the balanced alignment and then test both Balanced and Unbalanced
inputs to see which nets the best results with your particular antenna.
Stagger Tune the IF or Peak Adjustment of the IF? - Stagger tuning will give the IF bandwidth the maximum flat top possible with the mechanical filter selected. Early receivers were "peak" tuned for maximum response and may give a frequency bandwidth somewhat less than the mechanical filter bandwidth. Stagger tuning was used on the later IF modules and does give a better response in the receiver that is generally flat out to the limits of the mechanical filter's bandwidth. You can align early IF modules using the Stagger Tune method. Be sure to check the IF transformers to verify that the Q-spoiler resistors are present. Some IF transformers were modified by clipping out the Q-spoilers to have more IF gain but this also narrows the bandwidth. The Q-spoilers should be installed and connected for the best bandwidth. Updates to TM11-856A have the later procedure for stagger-tuned IF alignment, as does TM11-5820-358-35, or it can also be accessed from many sources on the Internet.
IF Cans without the Alignment Hole - Early production IF modules will have shields over the IF transformers that don't have a hole for alignment. This was to assure that the receiver's IF alignment wasn't tampered with in the field. When the receiver went back for repair or alignment the technicians had a set of covers with holes that were installed for the alignment and when the alignment was finished then the "non-hole" originals were re-installed. If you can't locate an extra set of IF cans then it will be necessary to drill an access hole for alignment. All later IF shields had the hole anyway and many early ones are found nowadays with the hole already drilled since the TM directs the technician to drill a hole for alignment purposes.
Slug and Trimmer Adjustments - One caution on adjusting the slugs and trimmers for the RF alignment. First set the Veeder-Root counter on the R-390A to the specified frequency. Then set the RF Signal Generator to its specified frequency. You'll notice that by "rocking" the Signal Generator frequency that there is a "peak" output on the Diode Load that is very slightly different from the Veeder-Root counter setting. Be sure to use the "peak" Diode Load voltage set by the Signal Generator frequency adjustment. Once you've set the signal generator to have the peak Diode Load voltage, then adjust the proper slugs or trimmers for further maximizing of the Diode Load voltage. Remember, the slug adjustments don't affect the receiver's frequency readout accuracy. That's a function of the PTO accuracy and the Crystal Oscillator. Always set for the "peak" response by "rocking" the RF Signal Generator and then adjust that band's slugs and trimmers for maximum output on the Diode Load.
|What to do
about early IF modules without the Mechanical Filter trimmer caps? -
The trimmers were added with the 1956 contract R-390A receivers. The
earlier IF modules will have fixed-value 110pf mica capacitors to tune
the input and output of each mechanical filter. When checking these
earlier IF modules, it will be necessary to measure the output and see
whether or not each of the Bandwidth positions (16kc, 8kc, 4kc and 2kc)
are more or less equal for a constant, known-value input signal. The
easiest way is to use the CAL and tune to zero beat and watch the
CARRIER LEVEL meter. For instance, if 16kc and 8kc measure 50db on the
meter but 4kc measures 40db and 2kc measures 50db, then something is
wrong with the 4kc mechanical filter. When doing this test, you'll
notice that the fixed tuned mechanical filters are not equal but are
usually fairly close - within 5db of each other. If the four filters are
not close in their equal response it will be necessary to reselect the
tuning capacitors on the filter that is different (hopefully, it's only
one filter that has been affected.) Try to select capacitors so that
each Bandwidth position results in a fairly equal output in all four
Bandwidths (mechanical filter derived bandwidths, that is.)
Make up an adjustable trimmer that has a range of about 80pf up to around 130pf. Remove the cover from the mechanical filters on top of the IF module and then remove the 110pf fixed capacitor on the particular mechanical filter. >>>
|>>> Now "tack solder" the trimmer in its place. Power-up the
receiver and select the bandwidth for the particular mechanical filter
and adjust the trimmer for maximum reading on the CARRIER LEVEL meter.
Remove the trimmer and measure the capacitance with a digital
capacitance meter. Install a silver mica capacitor of that value to the
mechanical filter. This may be enough to get the mechanical filter tuned
enough for equal response but it usually isn't.
To do the capacitance selection for the mechanical filter output will require accessing the underside of the IF module. You can loosen the BANDWIDTH and BFO knob-shafts and pull them forward. Then undo the IF OUTPUT coax cable and loosen the three captive screws. The IF module can now be lifted in the front and placed in a vertical position. Use rubber spacers to "prop up" the IF module. Remove the fixed silver mica on the particular mechanical filter and "tack solder" the adjustable trimmer. Power-up the receiver and switch the BANDWIDTH control for the particular mechanical filter and adjust the trimmer for maximum reading on the CARRIER LEVEL meter. Remove the trimmer and measure its capacitance and install that value silver mica on the mechanical filter. Replace the IF module and the knob-shafts and give the receiver a final test to see how the new tuning compares. Hopefully you'll be able to retune the mechanical filter to be within 5db of the other mechanical filters. Needless to say, the 1956 upgrade that added adjustable trimmers to all of the mechanical filters made everything a lot easier.
|I've used many R-390A receivers in my various ham radio
station set-ups over a period of many years. My first R-390A was a 1959
Stewart-Warner version that worked pretty well "as-is" when I got it
from a ham swap meet in 1991. I used it with an Eldico SSB-100F
transmitter I had and performance was great. A few years later I
obtained an excellent EAC version from 1967 but I sold it to buy a 1951
contract Collins R-390 installed in a CY-979 cabinet. I still own and
use the R-390 on a regular basis. I sold the 1959 Stewart-Warner after
obtaining a 1955 Collins R-390A. This Collins R-390A was given to me as
payment for repairing and rebuilding a Motorola R-390 for a fellow ham.
Eventually, I "wheeled and dealed" my way into a 1956 Motorola R-390A, a
1961 Capehart R-390A and a "Blue Striper" survivor from St. Jullian's
Creek Annex. In 2016, a bargain-priced 1967 EAC was purchased. It needed
a little TLC and turned into a great receiver. Another '67 EAC showed up
at a bargain price in 2017. I've used all of these receivers except the
"Blue Striper" at one time or another, both as an SWL receiver or as a
Here's what I like about the R-390A,...
1. If you absolutely must know exactly where in the electromagnetic spectrum you are listening, the R-390A and its family are the most frequency-accurate readout available in vacuum tube receivers. It's easy to achieve 1/2 kc accuracy or better. The mechanical-digital readout eliminates the vague interpretations of reading analog dials.
2. If you're bothered by QRM, remember the R-390A was designed to intercept radio signals from the USSR, China, East Germany and other Communist countries and be able to successfully copy those signals through any kind of interference whether natural or man-made. The mechanical filters allow the best in steep slope bandwidths. When operating CW, you can also switch in an 800 cycle audio filter. You can literally copy one CW signal with another CW signal almost on top (yes, I've done it,... many times.)
3. When the R-390A is rebuilt and correctly aligned it is very competitive as far as sensitivity is concerned. Are there more sensitive receivers? Of course, but sensitivity isn't all that's required to successfully copy weak signals. When all the available controls are taken into account and the user is very familiar with the operation and capabilities of the receiver, the R-390A is almost unbeatable as a station receiver.
4. Stability is the best in vacuum tube designs. Drift is non-existent.
5. You have two individual audio outputs on an R-390A. The LOCAL AUDIO is normally used to drive a 600Z ohm speaker set-up but you can also use the LINE AUDIO for the same thing - simultaneously! The LINE AUDIO was normally used to drive data devices like RTTY TUs, etc., but there's no reason it can't drive any 600Z load - like another speaker. I've set up a speaker in one room run by the LINE AUDIO and a second speaker in another room run by the LOCAL AUDIO. Independent audio levels in separate rooms. Really neat.
6. Everything about the R-390A's construction is "heavy-duty" and its use metal knobs imparts a massive "feel" to the receiver's operation. The R-390A has a certain impressive presence that attracts the attention of ham shack visitors. This seems to be true whether the visitor is familiar with the R-390A receivers or not.
|The following might be concerns
for some users,...
1. On SSB and the Meters - Although there were a couple of military SSB adaptors , the CV-591A (aka MSR-1 or MSR-4) and the CV-157, available and several modifications have been published and other add-on devices for demodulating SSB produced, none of these are necessary for demodulating SSB signals. Unfortunately, many new R-390A owners have only used modern equipment (with SSB Product Detectors) before going to the R-390A which only has a simple Envelope Detector. They expect the R-390A to be adjusted for SSB reception just like their modern receiver - RF GAIN at maximum with the AVC (AGC on the R-390A) on and volume level set by the AF GAIN (LOCAL GAIN on the R-390A.) The R-390A can't be operated like that when receiving CW or SSB. Before product detectors came along it was standard procedure when receiving CW or SSB to reduce the RF GAIN and advance the LOCAL GAIN (AF GAIN) so that the proper ratio of incoming signal to BFO injection could properly demodulate either CW or SSB. AGC was usually turned off but it depended on the receiver. With the R-390A, AGC can be left ON to limit the maximum response, if desired. If the R-390A's BFO is properly set-up, its position allows selecting either upper or lower sideband. Now, you do lose the function of the CARRIER LEVEL meter in this method of reception but who cares? The CARRIER LEVEL meter measures DB over 1uV and its accuracy depends on the RF GAIN setting. If you were planning to use the CARRIER LEVEL meter for CW or SSB signal reports, most stations wouldn't even know what you're talking about when your report was so many "db over 1uV." It's all a relative measurement anyway, dependent on the frequency and conditions. It's better to operate the R-390A as a standard pre-product detector receiver for CW and SSB and just give your contacts an estimated R-S-T report.
2. More on the subject of SSB reception and Modifications - The CV-591A family of SSB adapters were built by The Technical Materiel Corporation. These adapters work from the IF output, therefore you lose the Noise Limiter function, the 800 cycle filter function and the dual audio section of the R-390A receiver if you utilize only the audio output section of the CV-591A. Now, if you happen to have an extra speaker, you can connect one to the CV-591A output (8.0Z or 600Z) and the other one to the R-390A's LOCAL AUDIO (600Z only.) If you want to do SSB or CW you can use the CV-591A and its speaker. If you want to do AM, then use the R-390A's LOCAL AUDIO and speaker. The CV-591 will provide excellent, distortion-free SSB reproduction and they are well-worth using. The only disadvantage is the price that the CV-591A is fetching today, sometimes selling for as much as the R-390A .
On modifications to enhance SSB reception,...most of the mods that have been published do not improve the receiver's overall performance. Most modifications on any piece of vintage radio equipment will enhance performance for one area at the expense of overall performance. Besides, modifying a vintage receiver to make it operate like a "modern" piece of equipment seems to go against the whole idea of collecting, restoring, operating and preserving these classics in the first place. You're better off to learn how to use the R-390A properly and when you do, you'll find that modifications are not necessary for great performance in all conditions and in all modes.
3. On Audio Quality - Audio reproduction is not as bad as a lot of "AMers" complain it is. The mechanical filters provide a specific, very steep-sided bandwidth but some AM op-listeners are used to the "bell curve" that many early vacuum tube receivers had with only two fairly broad-tuned IF amplifiers. "Ringing" or a "hollow sound" were the usual complaints about the mechanical filter bandwidth. If you change the LOCAL AUDIO coupling capacitors to .022uf and then use a high quality 600Z transformer with a large speaker in a good enclosure, the audio sounds very nice, especially in the 8KC bandwidth (which is really close to 11KC) on AM with marginal signals or 16KC with a really great signal level (like from a retired AM-BC transmitter.) You'll have to do the same thing to the LINE AUDIO if you want to run dual audio lines to two separate speakers. If you're really into high-fidelity, then you can take the signal from the DIODE LOAD and run it through a shielded cable to a high-fidelity audio amplifier that's connected to a large hi-fi type speaker system. At 16kc bandwidth, AM signals will sound incredible. As with the SSB adapters though, you'll lose the NOISE LIMITER and 800 cycle audio filter functions with this "hook-up" unless you provide a separate speaker on the LOCAL AUDIO line (just in case you want to do CW.) For most users though, the stock audio sounds pretty good and with a good speaker the original .01uf coupling caps are fine.
|Here are some disadvantages to
using the R-390A - minor stuff, really,...
Break In Operation - The R-390A "Break In" function requires using a T-R relay with Normally Open (NO) contacts that change to Normally Closed (NC) when in transmit. This function operates the R-390A Break In relay and the R-390A Antenna Relays. The Break In function of the R-390A is opposite that of a typical receiver Stand By function that will require the T-R relay to provide a NC state for receive and NO for transmit. Most T-R relays, like the Dow-Key type, will usually provide a set of DPDT auxiliary contacts that allow connecting the R-390A Break In to one of the NO set of contacts.
The Weight Issue - No doubt, the R-390A is a heavy receiver weighing in at close to 80 lbs. Here's a hint for when you have to move the receiver. Remove the Power Supply module and the AF module. These two modules will reduce the weight over 15 lbs or more. With the covers off and the two modules out the receiver weighs about 60 lbs - much easier to move. Of course, you do have to get the receiver to the work bench to remove the covers and modules. This hint is for moving the receiver longer distances, like to another room (when you don't have a roll cart) or up and down stairs.
Cabinets - If you want the R-390A to be mounted in a cabinet you have two choices. First, is to find the proper CY-979 (or CY-979A) aluminum cabinet. This is a high-quality, military cabinet that is designed for the R-390-family of receivers. They are expensive. Originals were built from the early fifties up well-into the sixties. In the 1990s, an ad in Electric Radio offered CY-979 cabinets for about $150-$200. These cabinets were restored by W5MC and ink-stamped on the interior with an ID. There is some confusion on these restored cabinets as it wasn't clear in the ad if these cabinets were rebuilt old ones or new recreations. It doesn't seem likely that someone could have built a CY-979A complete with shocks and skids and then sell it for so little. But, since any original contractor ID was removed in the restoration process, the only ID is the ink-stamp inside which usually has a date with it (from the 1990s.) I've only seen one of these W5MC CV-979A cabinets and it was exactly like the original, with the screens inside the louvers, proper shocks and skids, etc. I would have to conclude that these W5MC cabinets are "restored" originals. If you are going for the CY-979 cabinet and you're willing to pay a high price be sure that the one you decide on has the shock mounts and the skids. It's fairly common to find CY-979 cabinets with the shocks and skids removed. These cabinets are incomplete and should be priced accordingly. For more details on the differences between the CY-979 and the CY-979A, go to the section on these cabinets at the bottom of this page. Other than the CY-979, any other cabinet that is for 10.5" by 19" panels with a depth of 15" will also work. Several sources sell a new Hammond cabinet of this size. Although advertised as a "R-390A Cabinet" it really is just a cabinet in which the R-390A will fit. Price is several times less expensive than the CY-979.
|Quick Check for Prospective
R-390A Purchases - The following "Quick Test" assumes
you are at the seller's QTH and have AC power available. The test
doesn't require anything other than the powered-up R-390A and can be
used for any R-390 or R-390A receiver that you are interested in
purchasing. Hopefully the seller will allow this easy test since you
don't need an antenna (a common excuse from sellers for not providing
information is lack of an antenna.) Though a loudspeaker connected to
LOCAL AUDIO would help, you don't actually need a loudspeaker but make
sure both LOCAL and LINE gain controls are set to "0" if a speaker (600Z
ohm load) isn't connected. If you bring your own 600Z ohm speaker, if
the seller is agreeable, connect it to the receiver LOCAL AUDIO
Put on the CAL and the BFO, set the KC to xx.500 kc and rotate the MC change thru all bands to hear if the CAL oscillator is received on all bands. Turn off the BFO, make sure the RF Gain is fully advanced and then, watching how much the CAL oscillator shows on the Carrier Level meter, run thru the bands again. The meter level should read over 40db. 50db is more likely if everything is aligned. Be sure to check all bands for CAL Carrier Level. With the CAL still on, check the EPE on any band. Be sure to also check the linearity every 10kc. That's an easy test that shows a lot. Recent alignment should have no more than 0.5kc EPE and an unknown PTO might have up to 4kc EPE but should still be linear with just a slight increase each 10kc increment. These two tests are easy to perform and tell you a lot of info. If both tests look good, the receiver is probably in good shape. This applies to any R-390A that you want to perform a "quick check" to.
Since the CAL oscillator is practically connected to the Antenna Input, it serves as a onboard signal generator. If you hear the CAL oscillator when tuning through the 100kc markers on all bands (if you have a speaker connected,) then most of the receiver is working well enough to receive a strong signal. The reading on the Carrier Level meter will show generally how sensitive and in alignment the receiver is. Most rebuilt and aligned R-390As will show 50db+ on the meter at around 10mc. Check around 5mc and the meter should read the same or higher. Check around 15mc and the meter will probably read less but still be around 40db. The EPE check just tells you if the receiver has been recently aligned by someone who is thorough and did do the EPE adjustment. EPE < 1kc, recent alignment. EPE > 4kc, typical of "as found" PTO.
You never know how a seller is going to react to this testing, so before doing any testing, be sure to describe what you want to do, what you're going to be looking for and why. Most honest sellers would welcome more detailed information on what they're selling.
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