Radio Boulevard
Western Historic Radio Museum

COLLINS RADIO COMPANY
51J Series of Receivers

Part 4

51J-4 Light Gray Panel - Collins Laboratory Version
51J-3 Converted to 51J-4 using the 354A-1 Mechanical Filter Kit
51J-3 SN:1999 "Tag-less" Version from 1952

     Back to Part 1        Back to Part 2        Back to Part 3 

Artwork from the Collins 51J-4 Manual 

51J-4 - Collins Lab Receiver - SN:4723

 Some Servicing, Some Restoration and a Performance Evaluation
followed a couple of years later by a PTO Calibration and eventually a full IF/RF Calibration

As the final version of the 51J Series one would expect the best performance to be from the 51J-4. The original market consisted of the commercial communications or laboratories users who had specific requirements with stability, dial accuracy and selectivity being at the forefront. Great audio wasn't a consideration since the bandwidth selectivity had to be kept narrow. The users today are all either hams, SWLs or collectors and this group definitely have different performance desires than the original purchasers had. 

The drawing shown to the right is from the 51J-4 manual. Drawing (A) shows how in a typical "bell-curve" type of IF the AM signal has the carrier placed at the center of the passband and both upper and lower sideband information is detected and reproduced. If one tries to tune "off frequency" to recover more audio highs it can be seen that the carrier would be reduced as the signal is tuned further from the passband center and eventually distortion will develop. Drawing (B) shows the 6kc mechanical filter's "flat top" passband curve and how it allows tuning one sideband and the carrier without loss of carrier strength. This allows better reproduction of the sideband information plus the carrier because the ratio of carrier to audio modulation is preserved.

It all looks good on paper and certainly works fine with strong, constant-level AM signals. But, that's not how 90% of the AM signals are - except for local AM-BC stations (most strong local AM-BC stations sound pretty nice on the 6kc MF tuned to either the USB or the LSB. Too bad the programming is so dismal.) Typical SW-BC stations fade, sometimes producing phase distortion, ratios of carrier to modulation change and cause distortion, sometimes there are heterodynes from other SW-BC stations. With ham AM signals the same problems can exist in addition to QRM, carrier frequency drift and low modulation levels. In the real world, tuning the 51J-4 for an AM signal using the 6kc mechanical filter as described in the manual will work well sometimes, especially on the AM-BC band, but with SW-BC or ham AM signals, much of time distortion and restricted audio are very noticeable. If you get used to tuning AM signals in this one sideband plus carrier manner (and conditions allow for it) the audio will have more highs and will generally sound like decent communications-grade audio,...most of the time.

51J-4 SN:4723 from 1960

As for the stock 51J-4, it was primarily for communications, not for aural-pleasure derived from band cruising using an ultra-wide bandwidth for high fidelity reproduction of idiomatic music transmitted by high-quality SW-BC stations (like China's Firedrake!) The basic 51J design was for data reception, not particularly for voice and certainly not for music reproduction. It's also important to remember that AM signals on the 51J-4 should be tuned to one sideband or the other. If you center the AM signal within the 6.0 kc MF passband then the audio will be restricted to 3kc and the audio will sound "muffled." The 51J-4 dial accuracy meant laboratories didn't have to have frequency meters anymore. Same with many of the military installations. Dial accuracy, frequency stability and excellent selectivity were what most users were interested in when purchasing a 51J-4. Great audio reproduction was not even considered since the passband had to be kept narrow for communications selectivity.

Having sold or traded off at different times formerly owned stock 51J-4 receivers, I swore I'd never buy another one,...ever! All it took to change my mind was seeing a light-gray panel laboratory version 51J-4. This receiver has a strikingly different appearance that stands out in the station landscape. And,...it's turned out to be a very interesting receiver since it has a Collins-installed "audio fix" for the 6kc MF position that allows decent AM reception.

51J-4 sn:4723 showing the top chassis and underneath.

Usually, a long warm-up time indicates a few to many weak tubes so the first thing to do was to test all of the tubes. All of the tubes tested very good BUT in the Mechanical Filter assembly one 6BA6 position actually had a 12BA6 installed. No wonder it took a long time to warm up. I momentarily thought the 12BA6 in the MF IF amplifier might have been some type of mod. Something like "install a low gain tube for reduced distortion" but I think it's more likely that was the closest "BA6" tube a former owner could find. With all good condition tubes, SN:4723 had much better sensitivity. I set the zero on the CL meter and could just get about a 10db increase by tuning in WWV, so sensitivity is not up to spec, yet. But, the Calibrator signal will drive the CL meter up to +60db so the problem might be the limitations of using a Pixel Loop antenna indoors (heavy wet snow took down my 135' Inv-vee Tuned antenna.) There wasn't any change in the audio quality, so I'm pretty sure the 12BA6 was installed because that was the only "BA6" easily available (out of the junk box?)   >>>

There was a lot of "crackling" in the audio output that seemed to originate in the MF assembly caused by a dirty tube socket (the one that had the 12BA6 installed.) Cleaned the tube socket with DeOxit to correct the problem.

The MF selector switch shaft slips a little and it must have been a long-term problem because the bristol screw that tightens the bell-crank lever to shaft clamp was virtually stripped of its splines so the clamp couldn't be fully tightened. Easy to replace, so I installed a good condition spline-head screw but, when tightened, the apparent "slipping" still occurred. The problem was in the bell-crank lever on the MF assembly switch shaft was slipping on that shaft because the set-screws weren't tight. After tightening the set screws the MF selector switch level worked like it should.

I'll run SN:4723 for a few more days to get some hours on the tubes before I do an alignment.

The ink-stamped number on the back of the chassis is "2" - that's all, just a single digit. Of course, the Collins tag has 4723 for the serial number. Navy-radio.com has a listing of several 51J-4 numbers and it looks like with the early production, serial numbers and the rear chassis ink-stamped numbers usually matched. By about SN:1000, this is no longer the case and the ink-stamped numbers become very low numbers while the SNs are four digit. There are a couple of exceptions, one as high as a SN in the 6000 block, but on most of the later 51J-4 receivers the SN and the ink-stamp number don't match but there are always exceptions.

Missing Screws - A pet-peeve, I guess. I bought all new 4-40 x .375" pan head, Phillips, SS machine screws along with flat washers and locking washers to correctly mount the bottom cover with all the same type of screws (19 screws are required for the bottom cover.) Bought three 6-32 wing-nuts and flat washers for securing the top cover correctly.

Test the IF alignment by tuning through a broad AM signal with the 6.0kc MC filter selected. Carefully listen to the signal as you tune from one end to the other. You should hear the AVC quickly attack at the low end of the passband, then the signal will quickly clear up and as you tune through about 2 to 3kc or so, the signal should stay constant and clean with fairly high audio frequency response. You will hear the AM signal narrow in audio bandwidth at the center of the 6.0kc filter but the signal level should remain constant with no distortion although with reduced higher frequency audio response. As you tune out of the high end of the passband, the audio frequency highs will increase for 2 to 3kc and then the AVC will react to the noise as the signal is quickly reduced by the steep slope of the mechanical filter.

This should be repeated for the 3.1kc filter and the 1.4kc filter also.

IF Gain Adjustment - One other thing though, if you have a later version 51J-4, it should be equipped with an IF Gain adjustment. This should be set last after the completed IF/RF alignment. The proper IF Gain setting was first accomplished at the factory, but that was over 50 years ago! Different tubes and component aging requires that the setting should at least be checked. The Collins procedure requires injecting 3uv into the antenna input at 2.1mc and then setting the IF gain pot for 270mv output on the IF OUT coax connector on the rear chassis. At the time this procedure was written measuring a RF level was commonly accomplished using a VTVM with RF probe and measuring the RMS voltage value specified. The manual assumes the alignment tech knows how to measure RF levels since nothing is mentioned in the procedure.

NOTE: This IF Alignment section is general information on how I align 51J-4 receiver fixed IF sections, not specifically for SN:4723 (until about two years later.)

Unneeded Alignment of SN:4723 - Jan 20, 2023 - After using SN:4723 for a few weeks, I felt the receiver was already pretty close in alignment. The fixed-IF was especially nicely adjusted because the Crystal Filter seemed to function just as it should. The date in 2013 that was written on a paper stick-on label stuck on the multi-section plug-in filter capacitor was probably when the receiver was last serviced and probably aligned at that time. There were a couple of checks that I performed however. First, I pulled all of the crystals in the Crystal Oscillator to check the sockets and pins for any corrosion and none was found. I then measured the Crystal Oscillator output and adjusted all of the trimmers for just under 2 volts. All of the trimmers had been set a bit lower in voltage but that was probably okay. Next, I aligned the Variable IF. Again, nothing was very far off from being in alignment and only needed slight peaking. Then the RF section was adjusted. This was only slightly off on a few adjustments. Last was the .5 to 1.5mc band and, again, nothing too far off, just a slight peaking of the adjustments. There weren't any problems with stuck trimmers or slugs, everything adjusted easily. A quick test using a ten foot wire "test" antenna on the AM-BC band and KOH 780kc pushed the CL meter to +80db. On the Pixel Loop, WWV 15mc pushed the CL meter to +40db (even WWV 20mc pushed the CL meter to +40db!) So, I've done alignments like this before. It's where you turn an adjustment only to put the adjustment back where it was. There were one or two slight adjustments needed but most were just "move and return" types.

About two years later, Dec. 2025, I did perform a full IF/RF alignment. All the details are further down in "PTO Calibration for 51J-4 SN: 4723."

All testing and listening for the past month has been with a Pixel Loop or with a 84ft sloper antenna (with tuner.) The 51J-4, now operating with the Collinear Array as the antenna, is like a "new" receiver. Strong signals on 80M, 40M and 20M are always present now. WWV on any frequency will push the CL meter to +50db or more. Coastal beacons in China are strong (XSG or XSQ on ~16.85-.98mc or on 12mc later in the afternoon) and even the coastal beacon SVO in Athens, Greece is an easy copy on 8.4mc in the late-afternoon as is TAH in Istanbul, Turkey. Utilities stations, like Trenton Military, are easy copy on 15.034mc USB with aviation weather (VOLMET) out of Canada (Trenton, Ontario is near Toronto.) Some of the SW-BC stations are incredibly strong, especially those out of China in the late-afternoon. Though Radio Havana puts in a very a strong signal here in Western Nevada, I think the broadcast-quality audio of the Chinese shortwave stations is superior to RH. These powerful SW stations sound pretty nice with the 12kc RC coupler switched in (even though it's communications audio.)

Strong signals make a substantial difference in the audio quality of the 51J-4. Weak signals are going to sound like "weak signals" and that's true for just about any receiver. A really good antenna does help provide more substantial signal levels with better audio reproduction results from the 51J-4. With antennas that are a "compromise," over-all performance will suffer somewhat. So, I like how this 51J-4 operates now with a full-size antenna and I do plan to incorporate it into a vintage station running with one of the Collins 32V transmitters.

UPDATE: Feb 19, 2023 - J-4 SN:4723 "on the air" with the 32V-3 transmitter running with the collinear-array antenna on 75M. No problems in Q5 copy of all stations. Used RC coupler position for 12kc bandwidth. Nice sounding!

UPDATE: Apr 1, 2023 - I've installed SN:4723 into a recently acquired, genuine 51J-4 Collins Cabinet. The loudspeaker is a 270G-3 I've had since 1970 (which is why it still has all of its original cream-color flocking.) The 51J-4 is now paired up with the W6MIT Homebrew "1625 Rig" which uses a T-368 Exciter to drive a pair of parallel 1625 tubes as the PA and another pair of push-pull 1625 tubes as the modulators. The 1625 Rig can produce 75 watts of AM carrier output power or 100 watts output in the CW mode. From this operating position the antenna used is the 234' Collinear Array.

PTO Calibration for 51J-4 SN:4723 - PTO SN:6667C.R.

Dec 23, 2025 - I've been having quite a bit of luck recalibrating the 70E-15 "CR" PTOs in the various 51J receivers. I'm down to the last receiver now, which is the Collins Lab 51J-4. Last time I tested the EPE I got 4.5kc so hopefully I'll find that the L002 trimmer still has some adjustability range so I can get the EPE down to <1kc. The formidable disassembly of the receiver isn't something to look forward to but it's necessary if PTO calibration is to be accomplished. It takes about one hour to disassemble the 51J-4 to the point where the PTO can "hang by its wires" out the bottom of the receiver. This position allows access to the front of the PTO to remove the hex-plug that covers L002 trimmer. A special unlocking tool is necessary to loosen the locking nut on the L002 shaft. V001 has to be temporarily taken out to be able to access the hex-plug which is removed using a 3/8" open-end wrench. V001 has to be then installed back in its socket. The only concern is that this receiver is a Collins Laboratory receiver and it must have gone through Collins calibrations many times. The last date on the Collins "test tag" is 1971. The concern is that the PTO has already been adjusted and 4.5kc is the best attainable EPE. Dismounting the PTO and testing the adjustment range of L002 is the only way to find out. This difficulty in accessing the front of the PTO was a deliberate part of the 51J-3/R-388 and 51J-4 design. It prevented casual tampering with the PTO calibration. Only a qualified technician would even attempt the amount of disassembly necessary. The photograph to the right shows SN:4723 with the PTO out and ready for calibration. Also visible in the photo is how much of the 51J-4 needed to be "taken apart" in order to have access to the PTO for calibration.

Initial EPE measured 15kc but this was just a "quickie test" and was performed after the hex-plug was removed (no green Loctite on the hex-plug so this isn't the first calibration of PTO SN:6667C.R.) I loosened the L002 locking collar. I connected the DFC to the PTO output at the coaxial cable end connection. A close look at the photograph to the right and the two index marks, one on the Oldham coupler face and one of the PTO frame, can be seen. I use the index marks to accurately know the position of each turn as referenced to the center of span, which is 2.500mc output f from the PTO. I performed a couple of L002 adjustments and got the EPE down to about 1kc but with a slight increase at the 3.00mc end. I tried another adjustment and went too far. The EPE actually got even worse. Another adjustment of L002 in the opposite direction hit just the right spot with an EPE of <1kc and a linearity deviation of  <1kc. I tightened the L002 locking collar with no change in the PTO output f noted. I removed V001 and reinstalled the hex-plug. V001 was then reinstalled.

A couple of minor issues were encountered during disassembly. Some of the set screws were coated with green Loctite. The Antenna Trim shaft coupler set screws needed to be heated with a small soldering iron to "melt" the green Loctite. The most difficult were the two set screws in the KC dial. These also had to be heated with a very small but long tip soldering iron to soften the Loctite. The KC dial absolutely MUST be dismounted in order to access the three PTO mounting screws so why these sets screws were coated with Loctite is a mystery. Another problem was the stud in the lower hex stand-off unscrewed itself and remained in the PTO frame. This made the PTO removal much more difficult than it should have been. When I had the PTO dismounted, I fixed the stud's mounting into the hex stand-off so I couldn't "unscrew itself" again. One other problem happened when I attempted to clean the KC dial. I always have used Glass Plus to dampen a paper towel for cleaning the 51J KC dials and have never had a problem with the numbers on the dial. On most dials, the numbers are under a clear outer layer of the composition of the dial and can't be harmed with cleaning. On some later dials found on 51J-3 and 51J-4 receivers (but not R-388 receivers) the numbers are on the outer surface of the plastic and the back of the dial is painted white. I've never had a problem with the numbers on these types of dials either. However, this 51J-4 dial did show a little fading of the red numbers when cleaning the surface with a Glass Plus dampened paper towel. Fortunately, I saw what was happening right away and stopped. Only the "95" and "0" red numbers show any fading and it's minor. So, be careful when cleaning these later 51J-4 KC dials.

PTO Calibration on 51J-4 SN:4723
Note the jumper wire for chassis connection for the ground lug and the paper towel wrapped around the various components so they wouldn't short to chassis. The note pad has the last EPE test showing <1kc of error and linearity deviation of <1kc.

Full IF/RF Calibration Required - Dec 24, 2025 - In reading what I wrote about the fixed IF alignment a couple of years ago, apparently I didn't perform an alignment of the 500kc fixed-IF. I wrote that I thought it was "close enough" at the time. Since I've gone through all of the trouble to make sure the PTO of SN:4723 is tracking correctly, I'd better do a complete receiver alignment. Probably not necessary but when it's completed then I'll know that everything has been put into proper alignment and the receiver is probably working as well as it should.

Well, the full alignment WAS necessary. Unexpectedly, the 500kc fixed-IF was off quite a bit. Even the adjustment for the mechanical filter assembly was significantly off. The Variable IF was off too. Since the PTO is tracking correctly now, it would be expected that the Vari-IF would be off since it's calibrated at the band edges. The RF tracking was off, probably because this time I was using the correct dummy antenna load. Also, I used the HP3325A Synthesized Function Generator for the 500kc IF and the Vari-IF which was probably more accurate than the HP-606B with a DFC for the signal source. I used the HP3325A and the FRNISI DPOS350P's Synthesizer for the RF tracking alignment. Modern equipment is so much more accurate it really makes the alignments much faster and a lot easier. About half of the alignment procedure in the manual consists of instructions for measuring frequency indirectly using heterodynes from the 100kc crystal calibration oscillator or using other receivers for measuring other types of frequency outputs. All cumbersome methods due to the limitations of the test equipment of the time. Modern test equipment allows measuring everything directly which is much quicker, much more accurate and a lot less of a headache. A full alignment using modern equipment takes about an hour.

Performance Improvement? - SN:4723 now behaves like all the other 51J receivers around here that have also had their PTOs calibrated. The big improvement was in the RC network in the 6kc MF position. Before there seemed to be a slight loss when switching to the 6kc position but now there's no change in amplitude between selecting 3kc MF or 6kc RC. Also, the audio response in the 6kc position has never sounded so good. I can only assume that having all of the 500kc fixed-IF aligned correctly is responsible for that improvement. As far as the Vari-IF and RF tracking,...KC dial readout is "dead-on" accurate,...the RF Gain on 20M SSB signals now averages about 7 or so with the AF Gain at 7. Although it depends on conditions, at 1530hrs PST, WWV 15mc was running at +50db on the CL meter using the Collinear Array. I tuned in XSQ on 16.850mc coming in very strong (Guangzhou, China marine CW beacon.) Big improvement on the audio from the SW-BC stations when listening in the RC 6kc position. The upshot is,...even though I thought the alignment was close,...it really wasn't very close at all. The 51J Series receivers can be moderately out of alignment and will still pick-up stations making the owner believe the receiver is working fine,...but all NOS (or test as NOS) tubes and a full IF/RF alignment will almost always improve receiver performance. Especially if that receiver is then used with a full-size, matched antenna system.

51J-3 to 51J-4 Conversion Using the 354A-1 Mechanical Filter Kit

51J-3 Collins Mfg. SN: 5282

Lots of Inept Repairs with Rampant Collateral Destruction, Loads of Missing Parts,...Extensive Restoration Definitely Required

When ordered from Collins, the 354A-1 Mechanical Filter Kit came with all of the parts and components necessary for the installation. Included with the kit was a 28 page manual with its 78-step list of instructions with appropriate "check-off" boxes after each step. The 354A-1 installation wasn't for beginners. It required a person with considerable experience, both mechanical and electronic, meaning that the conversion work would have best been performed by a professional electronics technician. This 354A-1 installation certainly shows what can happen when an inexperienced "technoid" takes-on a project that they aren't remotely qualified to do. This write-up is concerned with correcting a litany of self-inflicted, electro-mechanical problems involving the installation of the 354A-1 kit along with years of destructive, incompetent maintenance that has left this receiver almost a derelict.

Additional Note: I'm a long way from calling this receiver a genuine 51J-3. It has only one indicator and that's the lack of any military inspection stamps. The positive indicator, the PTO, isn't original and is a Collins replacement from the mid-1960s. The data plate indicator isn't the original data plate. Having a MFP-coated chassis applies to all 51J-3 and to all R-388s. So, with just a lack of mil-stamps, this receiver is just a "maybe 51J-3."

The photo to the right is how the receiver was shown on eBay in "as found" condition. As seen in the photo, the receiver had a 1951 R-388 data plate installed but I was sure it wasn't original to the receiver. The entire receiver was much dirtier than it appears in the photo. The chassis was covered with greasy grime and the front panel had streaking where rusty water had dripped down the panel. The red flare is from a window reflection. This is actually a very poor quality photo compared to the chassis photo from the same auction, shown below. At least it does show that all of the knobs were present and in good condition, the meter was correct, the bezel was undamaged and the condition of the front panel was decent.

1. No top cover (known in advance - kia.)
2. L-110 broken at the base, wire end of coil broken and the L-110 slug broken into two pieces and separated from the adjuster screw.
3. Crystal Filter control shafts not aligned with the front panel very well. Phasing control adjustment really "rough-feeling."
4. Drum dial cable isn't the original plastic covered metal cable but is regular "dial cord." It does work okay. Dial Drum is scratched in several places that align with the screws on the 354A-1 MF kit.
5. Bottom cover isn't MFP'd - not a repro, possibly from a J-4. Bottom cover was held in place with the typical "hamster one screw" - and it was a "self-tapping" sheet metal screw! Correct mounting requires the use of nineteen 4-40x1/2" Phillips screws with external tooth lock washers! (I ended up having to "chase" the threads on several of the 4-40 tapped holes used for mounting the bottom cover.)
6. Three of the tub capacitors (two electrolytics and one dual bypass) have been replaced with same type as the originals. They aren't MFP'd so they must be replacements. Also two ceramic disks and one resistor that are obvious replacements. Mostly original components. No mods to detector, BFO or AVC circuits.
7. The 3.1kc MF has a different exterior finish - kia. Later replacement? The 1.4kc and the 6.0kc MFs match with gray paint finish and metalized labels.
8. Removed the data plate and "5282" was ink-stamped underneath indicating this was the original front panel for this chassis. Data plate probably not original.
9. Aluminum scrap metal piece used for filter cap hold-down - kia. Undoubtedly a hamster fix.
10. AUDIO terminal block is a replacement type, not the original style or size - kia.
11. Grab handles missing - kia. Also, a few mismatched screws on front panel and two screws missing from the right side-panel to chassis and many more mismatched or missing screws, washers and nuts everywhere.
12. The 70E-15 PTO SN is 11277 from the mid-1960s making it an obvious replacement - kia. End-point measurement should be interesting (it was.)
13. The bushing that should mount in the 354A-1 MF Kit panel extension to provide support for the BFO/MF switch shafts is missing. Maybe it was never installed. The shaft coupler to the BFO is solid metal (homemade?) and the manual explicitly warns that only the supplied insulated coupler should be used or noisy operation of the BFO will result (it did.)
14. The rear support and thrust bearing for the ZERO ADJ. control shaft is entirely missing. Plated round-head machine screws are filling the mounting holes.

Overall, the receiver is quite a bit worse than the typical "as-found" condition and, although this inspection was mainly for mechanical problems, it does appear that this receiver can be repaired, refurbished and made operational. More details on some of the other problems follows,...

Dial Cord - This is actually called "flexible wire rope - extra small diameter - nylon coated" and it's available from McMaster-Carr. The original spec was for .015" diameter but, per the manual, .032" diameter was optional for repairs. McMaster has .024"dia and .032"dia. McMaster PN 8930T51 for .024"dia and PN 8930T53 for .032"dia. Original installation cables had brass crimp fittings but repair instructions indicate "knotting" was acceptable. I can salvage the cable from my "parts set" 51J-2. Although the Army TM R-388 manual states "nylon covered string" for the drum drive repair, all R-388s I've examined have nylon covered flexible wire rope for both the dial pointer drive and the dial drum drive. The AN/URR-23A Navy manual and the 51J-4 manuals call it "nylon covered cord." 

Non-original AUDIO Terminal block - I should be able to salvage a correct style replacement from the "parts set" 51J-2.

Crystal Filter Controls - There is an adjustment guide plate mounted to the backside of the front panel for adjusting the position and angle of the control shafts as they exit the front panel.

Filter Capacitor Hold-down - The 51J-3 should have a 5V4G rectifier tube which then uses the "flat" hold-down. Many times the 5V4G was replaced with a shorter 5V4GA tube and the "flat" hold-down couldn't secure the 5V4GA. Receivers like the 51J-4 used a "stepped" hold-down specifically for the 5V4GA tube. Sometimes, when a 5V4GA was installed in a mil R-388, the depot would cut the "flat" hold-down so that it only worked to secure the filter capacitor. I had a spare "half a hold-down" with the grommet still present. Since this filter cap hold-down was possibly a depot-modified piece, I installed it using a proper wing-nut.

Data Plate - One is never sure anymore whether a data plate is original to the receiver or not and a data plate that's mounted without locking washers is always suspect (like this one was.) The Collins production serial number of 5282 along with the MFP date of Oct 1952 seems late for a 1951 contract receiver with an early Mil SN of 33. Usually the Mil SNs were consecutive within the contract which should indicate that this receiver was among the earliest supplied on the 1951 contract. As said, one never knows anymore whether any data plate is original or not and I really doubt this one is. Since it seems possible that this receiver is a 51J-3, then what about a 51J-3 data plate? It undoubtedly never had one. Why else would someone install a non-original R-388 tag? A "tag-less" 51J-3 that was misidentified?,...possibly.

Dial Drum Scratches - These scratches are pretty deep and removed some of the dial background color. These scratches align with the screws on the 354A-1 MF kit. The installation instructions give explicit directions to cover the dial drum with heavy paper or other protective material to prevent dial scratching during the kit installation,...but who reads the instructions? Touch-up shouldn't be too difficult. The remaining sections of the dial are in very good condition so a new overlay isn't really necessary.

ZERO fiduciary adjustment control shaft bearing is Missing - Luckily, one of my "junk" R-388 front panels had this piece and the mounting screws and nuts and washers (same piece for either R-388 or 51J-3.)

Grab Handles - I bought a set off of eBay for $25. Included the correct mounting screws and locking nuts.

Soldering was an important clue to the level of workmanship. It's difficult to rework any electronic device that has been MFP-coated. However, experienced professional electronics techs that have been trained using the proper tools for cleaning the MFP'd joint, performing the rework, resoldering the joint and then recoating the joint with new MFP, will produce excellent quality workmanship. None of that happened. The MFP was burned-through with the soldering iron, the wire "ripped out" of the terminal, the joint not cleaned afterwards, the wire ends not reconditioned and, after the rework accomplished, the new solder joint wasn't recoated with MFP. Also, in examining the type of wire lead wraps, which should be a good clean full wrap of a properly tinned wire end, it was found that many of the joints weren't wrapped at all but were wires "pushed though a lug hole" and then soldered, which is just one step above "tack soldered" joints.  So,..."hamster work?" Definitely.

Since the receiver has had its "originality" as a stock 51J-3/R-388 destroyed, I won't feel too guilty in going through the receiver and correcting the quality issues with the goal of making the installation look (and function) more like a "professional rework job." Also, other quality issues, like the use of dial string for the dial drum cable or the missing or wrong types of screws and the litany of missing lock washers or the scratched dial drum, will be corrected. Where MFP should have been reapplied, I'll recoat using my mix of yellow-tinted lacquer that looks like MFP but doesn't have the fungicide in the mix. I might feel a little guilty going in and disturbing such a perfect example of incompetent electro-mechanical reworking technique, that while the installation does "sort of work" (which may have been all that was desired) shows the complete lack of professional technique that we all hate to see.

Collins Mfg. SN:5282 - Chassis as received

At 7.5kc EPE, it might be possible to adjust out the error but that's probably just a wishful reverie.

Rework Details

BFO and MF Switch Shaft Bushing - This piece was missing. It's a standard .250" shaft bushing that must mount with a panel thickness of less than .125 inches. The MF Kit panel is .060" aluminum with an over-size mounting hole to allow centering the bushing. Because of the over-size hole, two washers or adapter plates have to be used. Originally the assembly used a square shaped spring washer but the washers or adapters would also work fine. Found a .250" bushing that would work and made the square adapter plate out of .060" aluminum.

BFO Coupler - This was a more difficult piece to find. As mentioned, the receiver has a homemade solid brass coupler. The 354A-1 instructions are explicit that an insulated coupler has to be used to avoid noisy operation of the BFO. Unfortunately, one side of the coupler has to interface with the 3/16" BFO coaxial shaft from the front panel and the other side of the coupler has to interface with the 1/4" shaft from the BFO LC assembly. I found an insulated coupler that was for a 1/4" shaft on one side and for an 1/8" shaft on the other. I just enlarged the 1/8" hole to 3/16" (used successively larger drill bits to keep the hole centered.)

Broken AVC Switch - This is a fairly common problem. Only half of the switch is actually used and normally the half that would break off was the unused section. Since it didn't affect operation, a lot of the broken switches were left in place. However, these fiber board switches are extremely fragile and have become even more fragile after three-quarters of a century of existence in some types of environments. This AVC switch broke when I was cleaning it and that was when gently cleaning with DeOxit and a small paint brush. At least I had the broken piece.  It's very easy, if you have the front panel dismounted, to use epoxy to repair the broken switch. As mentioned, only half of the switch is used so it's not ultra-critical in its operation but it should have good alignment so the switch operates easily. I applied the epoxy with a wooden toothpick and was careful to not allow the epoxy to "run" into the contacts. I used just enough to hold to broken piece securely. The reason only half of the switch is used was so Collins could use the same type of switch for four different switch applications, AVC, BFO, LIMITER and CALIBRATE.

Cleaning Chassis and Front Panel - The chassis top was covered with greasy grime. I used WD-40 to cut the grease and cleaned the WD-40 residue with Glass Plus. R-388/51J-3 chassis will usually clean-up quite well because of the MFP coating protects the metal from corrosion (most of the time.) I used acid brushes, small paint brushes and Q-tips along with paper towel strips for cleaning the chassis.

The front panel had to be dismounted and completely stripped of parts for a thorough cleaning using Glass Plus and a variety of brushes. I inspected the front panel carefully to see if I could find any residue of orange SC acceptance stamps but there didn't seem to be any indication of mil-stamps. Most of the time with wrinkle finish I can use a brass bristle brush in a gentle motion to remove thick grime in the wrinkle convolutions. Otherwise, acid brushes and small paint brushes are used. I was very careful around the "1KC, 3KC and 6KC" nomenclature since that wasn't original silk-screening and consequently was extremely faded. While cleaning didn't damage it, it didn't improve it either,...it's still pretty faded. Once the front panel was clean, I touched up most of the nicks and scratches using Artist's Acrylic mixed to match St. James Gray. Then the front panel was given a rub down using "3 in 1" machine oil to bring out the luster. Excess was wiped off and the following day another rub down with oil and wipe off the excess. This treatment lasts for several years.

KC Dial Oddity - I thought this KC dial looked slightly different from the front. The white background seemed to be very slightly "streaked" as if it was brush-painted on. Also, the numerals were slightly thinner and somewhat pale looking. Once I had the KC dial dismounted and could look at the backside I found that it was painted! This KC dial is different than the normal R-388/51J-3 dials in that the numbers and scale index are engraved into the plastic on the backside. Then the numbers and scale index were filled with the appropriate red or black paint and then the entire back painted with a semi-transparent thin white paint. All R-388 KC dials I've seen were plastic laminations with no engraving. So, where did this KC dial come from? I've had a report from another Collins collector that found this same type of dial also installed with/on a replacement PTO. UPDATE: I've also found this type of KC dial on the Collins Lab 51J-4 and 51J-3 SN:1999. Maybe the type of KC dial manufacture used for non-military receivers.

AUDIO Terminal Block Replacement - I found a NOS terminal block that was identical to the original but it looked so new that it was obvious that it was a replacement. I removed the AUDIO terminal block from the 51J-2 "parts set." It was in good condition and showed the patina of age that made its installation look original. One would think that there wouldn't be any problem with such an easy task but,...the non-original type of terminal block had mounting holes that were spaced slightly further apart than the original. In typical hamster fashion, instead of modifying the part, another hole was drilled in the chassis apron to mount this incorrect part,...unbelievable. I filled the non-original hole with epoxy and touched it up to match the MFP color of the chassis. The installation of the correct type of terminal block was easy. Oh, and of course, the incorrect part had been mounted without lock washers so I had to install the correct #4 external tooth locking washers when mounting the original type part (sometimes Collins would mount terminal blocks without lock washers but would use green Loc-tite to secure the screw and nut.)

New AC Power Cable - The original cable was dried-out and split in several places. Also, the wire insulation inside the cable had cracked and split so replacement was going to be necessary. The original power cables were two conductor which was standard for the early-1950s. In many installations, especially military ones, the AC power was fully-floating, that is, the neutral didn't really exist. It didn't really matter how the AC cable was connected since polarized plugs and grounded neutrals were somewhat in the future. Nowadays, unless you operate the receiver from an isolation transformer, one side of the house AC is grounded at the breaker box and that side is supposed to be the NEUTRAL. Since this is the case, I just go ahead and install a three conductor power cable. In this installation, the HOT (the black wire) is connected to the rear of the fuse holder. The NEUTRAL (the white wire) connects to the tie point strip terminal on the side chassis wall. The GROUND (the green wire) connects to the adjacent terminal on the same tie strip that is the grounded terminal. When installing the AC plug, brass screw terminals are HOT, silver screw terminals are NEUTRAL and green screw terminals are GROUND. Keep the chassis-side wires as short as is necessary to make a nice looking routing to the connection points.

Reworking MFP Joints on L-110 - The next repair attempt required removal of the entire fiber board assembly to allow better access to maintain alignment and also not have epoxy going down the barrel. There are seven wires that have to be unsoldered and then four screws removed to dismount. The main difficulty is unsoldering the wires when they are vinyl-insulated wires that are coated with MFP. While the typical method is to scrape the solder joint with either a small solder-aid wire brush or a X-acto knife to remove the MFP first before then using Solder-Wick or a solder extraction tool, the heat involved usually will severely damage the vinyl insulation on the wires. The only method that saves the wire insulation is to clip the wires and leave about a .125" stub on the coil assembly side. When reinstalling the coil assembly the stubs will have their insulation removed and the wire stub tinned. Then the proper wire from the circuit is stripped of about .125" of insulation and tinned. Then a helicoil made out of 26 gauge copper wire is used to create a soldered "butt joint" that has good mechanical and electrical properties. Since the helicoil (looks like a small coil spring) is up against the terminal on the coil assembly it almost goes unnoticed and additionally it can be MFP'd to look like an original connection.

L-110 Broken at the Base of the Coil Form
 

L-110 Repaired and Ready to Reinstall

Coil L-115 wasn't pushed-in the mounting hole enough to be "snapped" into the fiber board correctly. I wondered why it had been setting slightly tilted and could easily be moved when I was doing the inspection. Once the fiber board assembly was out of the receiver, I could see that one side of the spring retaining tangs wasn't "sprung out." A little manipulation with the tip of the X-acto knife got the tang to "spring" out and fully support L-115, which is now straight and secure.

Reinstallation of L-110 into the R-388 - I had a triple-marking for the correct wire installation. First, a drawing showing the where each wire went based on color code and then where each of the wires went by number and then each wire had a small piece of blue masking tape attached with the proper number. It made for a very easy reinstallation. The helicoils eased the soldering job. Once the wires were soldered, they were double-checked using the listed color code. I robbed a L-110 slug out of the 51J-2 parts set and installed it in the R-388. Mechanically, the travel of the coil was excellent and straight. In operation, I could tune in 100kc markers but no other signals. Since there was no change in L-110 throughout the entire 51J production, I think the 51J-2 slug should have the required permeability. Hopefully, alignment corrects the AM-BC operation.

BFO Noisy - What the 354A-1 manual says about using the insulated coupler is absolutely true. The BFO, with its solid brass coupler is noticeably noisy in operation sounding almost "microphonic" in nature. I disconnected the coupler from the shaft and then merely adjusted the BFO by turning the coupler with my fingers and, as expected, no noise. The lack of the bushing to support the MF switch shaft results in excessive lateral movement of the BFO knob and the movement of the 354A-1 assembly when operating the MF bandwidth switch. Both of these problems are easy to solve even with the receiver back together.

R-142 3rd IF Amplifier Plate Load - This 1 watt CC resistor had been replaced sometime in the past and it was obviously a poorly accomplished repair since the end going to the IF transformer was wrapped around a lead from a capacitor going to the same point. Since the MFP wasn't cleaned off, that joint was a cold solder joint. R-142 was unsoldered, the joints prepared correctly and the resistor resoldered in its correct location.

I had noticed before that in tuning the receiver, the frequency change was very slightly "jittery" - not mechanically but in the actual frequency change. That problem was now gone, the tuning change was smooth as it should be. A surprise was that the modulated hum was gone. I think the fact that the PTO case wasn't really grounded very well had something to do with it.

The tuning did seem a bit tight. I thought that probably with the loose screws and one missing screw, the so-called tech had probably adjusted the oldham coupler for that set-up which now, with the proper PTO mounting, left the oldham coupler with very little (or no) clearance. I loosened the set screws on the front section of the oldham coupler and slightly moved it further forward on the shaft to have some slight clearance between the three pieces of the coupler, then the set screws were snugged up. That fixed the "tight" tuning and now it feels like a typical R-388/51J-3 when tuning.

I had also corrected a ground on the MF Kit installation that had a tie point ground lug mounted on top of MFP with no locking washer (to cut through the MFP.) I cleaned the MFP off of the area AND installed a locking washer for a good solid chassis ground. With the modulated hum gone, I reinstalled the original dual section filter capacitor and it worked fine now.

The insulated coupler was one I found in the spare parts. It looked close to the original and had a 1/4" opening on one side and 1/8" opening on the other side. To enlarge the hole I drilled using incremented drill bit sizes to easily finally drill the hole at the required 3/16" diameter. That was all the coupler needed to have done to it to work correctly.

There's a procedure in the instructions to have you adjust the bushing position, then dismount the 354A-1 box to allow tightening the bushing nut and then remounting the 354A-1 box. Of course, this is all supposed to be done before the kit is wired into the receiver. Since it was never done, I had to adjust the bushing with the shaft in place and then carefully use a long blade screwdriver and "wedge" the nut flats as tight as can be done in that manner. There's not enough room for a wrench unless the MC dial drum is dismounted. Well, the "wedging" worked fine.   >>>

The last step was to "rough set" the BFO, just to make sure everything worked correctly. With all of the mechanical parts installed like they should have been years ago, the receiver now operates the BFO noiselessly with no microphonics. MF switching doesn't move the entire MF kit assembly now.

I just can't believe that this 354A-1 was installed this poorly,...and apparently functioned to a level that satisfied the owner. But, then on the other hand, he probably blamed Collins and the 354A-1 kit for the performance problems rather than his own incompetence.

But wait,...there's even more,...

I had a good condition BFO assembly still installed in the "parts set" 51J-2. The BFO assemblies are almost identical with the two NPO capacitors being the one obvious difference. Since the BFO circuit is essentially the same in all 51J receivers and just two NPO capacitors were added for the later units, I decided to go ahead and install the 51J-2 BFO in this 51J-3. I swapped the shield-can so the BFO assembly would look original and performed the installation. I had a slight diversion to clean the chassis area since the can was off and I also discovered that the second IF transformer had very loose mounting nuts that needed to be tightened. Once the 51J-2 BFO was fully installed, I powered-up the 51J-3. The BFO seemed to be much stronger and a lot more stable than what I had been experiencing before. I'll have to notice if there is any BFO drifting without the NPO compensating capacitors. 

Black electrical tape is always a good sign, right?
Covers up the broken fiberboard and unsupported terminals

51J-3 SN:5282 - Under the chassis of a typical R-388/51J-3 that was always MFP-coated. This shows a touch-up of the newer solder joints and the new tub capacitors using my Yellow-tinted Lacquer (fake MFP.) I used a small paint brush which is probably how MFP touch-ups would have been applied at a mil-depot. Note the green slug in L-110.

500kc IF - The 500kc IF requires a series RC shunt lp filter as a load but one has to be careful on the plate side adjustment since B+ is present. This moving the shunt to both the input and output sides of each IF transformer is probably the biggest headache in doing the IF alignment. If you have the shunt already made-up with the 4.7K resistor in series with a .01uf capacitor with about 5" flexible wire leads with small alligator clips, it becomes a whole lot easier. Only one lead has to be moved since the other is always at chassis ground. The 354A-1 alignment instructions say to turn off the receiver when moving the shunt because of the B+ on the plate side of the IF transformers but, interestingly, no other 51J manual has this warning.

The IF section was way out of alignment but nothing unusual was found in the IF alignment and it went smoothly.

Variable IF and RF - Again, this section of the receiver was also way out of alignment. I suspected that the ANT/RF slugs and trimmers would be out of alignment because the ANT TRIM was resonant for 50Z loads at fully unmeshed. The ANT TRIM variable condenser must be set to half-meshed before aligning this section of the receiver and the proper dummy load between the RF signal generator and the receiver must be used (47 ohm in series with a 100pf cap in series with the RF signal generator.) A couple of the trimmer capacitors were slightly stuck but came loose with a gentle movement. There was one stubborn trimmer that refused to budge. I used a hand-held heat-gun to apply heat to the trimmer. About 15 seconds of moving the gun around was all that was necessary. The trimmer became "unstuck" very easily. The heat-gun is the safest method to loosen stuck trimmers. The rest of the Vari-IF/RF alignment went normally,...except,...

I suppose this broken wire could have been collateral damage from the L-110 break BUT even that broken L-110 was mysterious since there wasn't any physical evidence as to what caused the breakage. If someone wanted to disable just the AM-BC band while leaving the rest of the receiver working fine and to have "fixing" the disabling be rather involved, breaking L-110 and cutting the plate wire from L-124 would be a very easy way to accomplish that. But why? Commercial use and preventing the "goof-off" employees from listening to AM-BC on a company receiver? Who knows? Probably just more collateral damage.

Wrap-up - April 22, 2023 - I need to find a top cover for this 51J-3/51J-4. Also, in the future is a 70E-15 tweak. If I ever locate a "parts set" R-388, I'll swap out the BFO coil assembly. Otherwise, the receiver is now a pretty good example of a possible 51J-3 receiver that has had the 354A-1 Mechanical Filter Kit installed.

After the alignment, a casual test listen checked in on Trenton Military on 15.035mc, aviation weather out of Trenton, Ontario. Also, XSG and XSQ, the Chinese Coastal Beacons on 16.898mc and 16.952mc. On 20M, a 9V2 station and a VP2 station were easy copy. A couple of CE stations from Chile and W1AW CW bulletin on 17M. Also, I tuned in XSQ on 16.952mc and left the receiver on for about an hour. I never had to retune and the CW and "chirping" never changed pitch in that time. I don't think the 51J-2 BFO coil assembly will be any problem.

Stations on 40M are pretty strong with the usual west coast variety of hams on in the afternoon. Audio quality is "typical 51J-4 mechanical filter" with very strong stations, like AM-BC, not sounding too bad. Weak AM stations (SW-BC usually) are pretty bad because the phase distortion limits which sideband you select since the "best one" always seems to change.  

SSB is pretty good but of course the BFO to signal ratio has to be controlled and distortion happens on strong SSB signals, especially found on 40M and 80M. RF Gain has to be below 8 for most strong SSB signals and below 7 for the blow-torch signals. SW-BC normally sounds poor but in the late afternoon, the Chinese SW-BC stations show up on 23M and they are very strong signals that reproduce quite well, even though the audio quality is limited by the 6kc mechanical filter. Also, the Crystal Filter operation is excellent now.   >>>

51J-3 SN:5282 - Showing the MF Kit, the Newer PTO and a clean chassis. If you have sharp eyes, note that the lower screw on the dial drum bracket is missing. Discovered that about two months after I took this photo.

51J-3 Collins Mfg. SN: 5282 with 354A-1 Mechanical Filter Kit Installed - Restoration Complete

Wrap-up - At first I thought this receiver was almost beyond hope. It had A LOT of things wrong with it. Years of rough treatment, years of incompetent and destructive maintenance with an utterly dismal quality of repair work and countless missing screws and locking washers. But, the initial close inspection revealed that most of the receiver was in decent original condition and still in pretty good shape. Only where the receiver had been "worked on" was there rampant damage. After about ten days of "reworking the rework" I was finally able to correct all of the problems and everything now operates as it should and looks like it should under chassis. Ultimately, the receiver cleaned up quite well which actually allows the overall nice condition to be easily visible. Now SN:5282 looks like a "well cared-for" 51J-3 ("without data plate" type) and, best of all, it works like a R-388/51J-3, too. Plus, it has mechanical filters - a "kit-type 51J-4," but wait,...aren't all 51J-4 receivers like that since all J-4s have the 354A-1 installed.

UPDATE: Apr 28, 2023 - I went through all the tubes and tested them again. The PTO tubes were weak. NOS 5749/6BA6W tubes usually test about 70 on a TV-7. Minimum is 41. The PTO tubes tested 38 and 22. Most of the IF tubes were between 40 and 50, so not terrible. I installed all NOS 5749/6BA6W except for the CAL oscillator that got one of the best used 6BA6 tubes. I had to do a minor tweak on the BFO and on the CAL oscillator afterwards. I also replaced one of the 12AX7 tubes with a "tests as new" tube and both 6AK5 tubes with NOS tubes. With the best tubes installed, now SN:5282 runs 10mc WWV up to +48db. During the winter, the reception level would have probably been +55db or more. Typical pre-summer poor propagation.

UPDATE: June 5, 2023 - Although the BFO coil from the 51J-2 has been functioning fine in this receiver, I did want to install a correct R-388/51J-3 BFO coil eventually. I was able to purchase (off of eBay) a set of IF transformers and the BFO coil that had been taken out of a R-388. The BFO coil will be installed into SN:5282 to replace the 51J-2 BFO coil presently installed. Also, planned for SN:5282's return to the workbench is to apply dry transfer letters-numbers for "1KC", "3KC" and "6KC" since the lettering at present can hardly be seen. Lettering size is 1/8" and the font that's closest is R R Gothic. Color is white. The lettering that is present isn't even close as far as the font type used and the placement of each group is too close to the chrome switch lever. I'll probably have to apply a little "touch up" paint first to hide these transfers and then apply the new, more correct style with the proper spacing from the switch lever.

Back on the Bench - June 22, 2023 - The 51J-3 was on the bench. The 51J-2 BFO had been removed and I was ready to install the replacement R-388 BFO.

BFO Assembly Problem - I inspected the replacement BFO closely because it's very easy to correct any problems found now before the BFO is installed. Lucky that I "looked first." I noticed that the BFO shaft was rough-feeling when rotated and there was a very slight "metal to metal" contact sound. A closer look and I could see all of the variable-C plates were shorted together. The plates weren't bent but the rotor had changed position (probably the retaining clip came off) and that resulted in the rotor plates shorting against the stator plates. I thought about bending the plates to get the clearance but replacement of the variable-C was actually the best option. Luckily, the variable-C in the original R-388 BFO was okay. There are only three connections to the variable-C, so the transplant wasn't difficult. Interestingly, I looked at all three variable-C components (51J-2, R-388#1 and R-388#2) and all three were different. All three had different part numbers stamped on their ceramic bases. The 51J-2 and #1R-388 had the same number of plates but #2 had two less plates. NPO capacitors were also different styles between #1 and #2. Obviously, these were minor variations in components used from different vendors throughout the production runs and these variations don't affect the operation of the BFO noticeably. So, the variable-C from the original BFO assembly was removed and transplanted into the replacement BFO assembly.

MFP inside the BFO Can - One thing observed was that the solder joints on the BFO assembly were all MFP-coated (and this would be inside the BFO shield-can!) This means that MFP-coating was a process that took place at all stages of assembly, even at the component assembly level (since these types of components wouldn't get MFP-coated with the final application, it had to be done ahead of chassis assembly.) The transplant was slightly complicated by the MFP since the solder joints had to be scraped cleaned first, then "solder wicked," the wire unwrapped and the Variable-C removed by dismounting the two screws and washers. The same steps had to be performed for both the donor assembly and the assembly being repaired.

Mechanical Alignment - Once the transplant was complete, the BFO assembly was installed into the "original to this receiver" shield-can, the BFO coupler installed and the entire assembly loosely mounted. The alignment of the BFO shield-can to the Mechanical Filter switch assembly is why the BFO can't be mounted tightly at first. Once the BFO shaft is installed and the BFO assembly and shield-can and the BFO coupler all line-up, then the nuts can be tightened (under the chassis.) Next, the three TC wires are connected and soldered. The ground wire TC had been cut at sometime in the past and then tack-soldered with a glob of solder. I removed this wire and installed a new 18ga TC wire soldered from chassis to the BFO terminal.

Test and Alignment - The receiver was connected up for normal operation. Upon power-up, there was no indication that the BFO was operational. But, I turned on the Calibrator and tuned in the heterodyne for a good strong signal. By turning the BFO on and off, I could hear that the BFO was coming on but was "way off" frequency. I had pre-set the BFO vari-C for zero-beat (half-mesh,) so the main L adjustment was off,...and off by a lot!. I turned the L adjustment about five full turns before I heard the heterodyne coming close to frequency. It probably was off that much because the variable-C had two more plates than the one that I had been removed. Anyway, I did a typical BFO alignment and everything was working fine.
 

Dry Transfers for 1KC, 3KC and 6KC Nomenclature - I did a couple of tests to see if I could actually apply these letters and numbers with the panel mounted and all of the knobs in the way. The BFO knob and the MF Switch are in the way. The escutcheon is in the way. The panel is vertical which makes letter alignment difficult. The only way to do this lettering so that it looks professional is to dismount the panel and dismount most of the parts. The grab handles can be left mounted but anything the keeps the panel from laying flat on the bench had to be dismounted. Once everything is out of the way, then dry-transfer alignment of the lettering is much easier. I even did a practice run using a "parts set" stripped R-388 panel and found that letter alignment is pretty easy when the panel is stripped of parts and is laying flat. The next step was to dismount the panel from SN:5282. I've done this operation so many times it seems pretty easy now. I keep all of the removed parts organized and safe which helps when it's time to reassemble. I left the meter mounted but I did dismount the escutcheon. The panel was now ready to get started with the lettering. The photo to the right shows the 1KC, 3KC and 6KC nomenclature as it was originally. Very faded and not the correct font.

Touch-ups and Pre-alignments - I thought it would look better if I completely covered the old extremely faded MF nomenclature. They were too close to the MF switch lever so they would show a little if I left them. I used matched St. James Gray paint and used just barely enough to cover the old lettering. I had to mark in pencil where the MF switch positions would be to have a letter alignment point (when finished the pencil marks were covered with the St. James Gray paint.) I used to do this type of dry transfer lettering quite a lot on prototypes and on test fixtures where I used to work, so I've had considerable experience with dry transfer lettering. Trouble is, that was over 30 years ago,...but I think I still remember how to do it. The 51J-3 panel is sort of easy because it already has a lot of nomenclature on the panel that can be used for reference alignments. The dry transfer letter sheet will have alignment lines along with observing the line along the tops of the other letters that will help keep the position of the transfer sheet straight. I had to use the MC dial cut-out edge for a straight reference along with the alignment lines on the transfer sheet. The letters and number really have to be close to perfect in being straight and spaced evenly. If well-done, the lettering will look original,...even if the font is slightly different from what Collins used. The other thing that really helps is each position only has three characters, a number and two letters. That's much easier to keep straight than long words or multiple words on one line. Three characters is nice.

"Toning Down" and Added Protection - Once the application of the transfers was completed it was obvious they were "bright white" which wasn't totally unexpected. Although the other original nomenclature looked really white, it wasn't, since it had years of aging that had discolored it somewhat. I had to "tone down" the new white nomenclature to match the aged nomenclature but whatever I used to do that had to be colored but transparent. I thought it would be a good idea to experiment first since the dry transfer application looked really good except for being very white. I applied some dry transfer letters to the "parts set" R-388 front panel and began to experiment. I tried dark tea, Polyshades Walnut and Artist's Acrylic gray paint mixed with tea. The last two worked pretty well with Polyshades doing the best at a match. The added benefit is that the instructions for the 354A-1 kit indicated that the decal originally supplied with the kit should be coated with clear lacquer for protection, so the original MF conversions had a coating on the 1KC, 3KC and 6KC nomenclature. I applied the Polyshades to the 1KC, 3KC and 6KC nomenclature with a very small paint brush with very light coatings to "work up to" the best match. The Polyshades has to dry for a few hours before the lettering could be touched,...if you wanted to touch it.
 

Reassembly and Testing - While I was reassembling the receiver I happened to push against the MC dial drum and it physically moved to the right somewhat. I saw that both mounting brackets moved. Unbelievably, I found yet another "missing screw and lock washer." The left bracket had both screws but they weren't tight at all. The right bracket had only one screw and it wasn't tight either. Strange that the screws that were present had their lock washers. A 6-32 RH Phillip's machine screw and external tooth lock washer was installed and all mounting screws for the brackets were tightened. Guess I missed that one,...until now. No other issues. Bottom cover installed and top cover installed to complete assembly. UPDATE: Oct 27, 2025 - Performance Test - It's been a while since I've operated this receiver so I connected it to the Pixel Loop antenna and attached a 4Z loudspeaker. On the 26th there was a ham contest so 20M was loaded with signals. I went up to 15M and heard some JAs and some CE stations. Copied XSQ 16.874mc and Trenton Military 15.035mc USB. Also, a "Numbers Station" on 15.015mc USB although the transmission was using phonetics and in English. Good performance, especially considering I was using the Pixel Loop. The next day I tried the Collinear Array antenna and that was quite a noticeable improvement. XSG copied on 16.896mc out of Shanghai, China, another maritime CW beacon that's a little more difficult to receive than XSQ (Guangzhou, China.) UPDATE: Dec 19, 2025 - PTO Calibration - A few days ago I decided to try calibrating a spare 70E-15 PTO I had. The EPE on this spare was an unbelievable 15kc! Yet, with about four adjustments of L002, I had the EPE at <1kc and the linearity was about 1kc. The ease of that calibration got me thinking about the PTO in SN:5282 with its EPE of 8.5kc. This was going to be a more formidable project in that this PTO had be dismounted from the receiver in order to do the calibration. It took about an hour and a half to disassemble SN:5282 to the point where the PTO was "hanging" by its wires but ready to calibrate. Again, I was surprised that with about four adjustments of L002, I had the EPE at <1kc and the linearity deviation was about 1kc. Receiver reassembly took another one and a half hours. Then I thought that I better realign the entire front end of the receiver using the correct 51J-4 dummy antenna (I just used a 47 ohm resistor before.) I was surprised to find that I hadn't really adjusted all of the Crystal Oscillator trimmers. It also appeared that I didn't do the 16mc to 30mc tracking alignment either. Most of the adjustments were close but several were quite a bit off. Now, SN:5282 has "dead-on accurate" KC dial readout (like a frequency meter) and has excellent performance on all bands.

51J-3 converted to 51J-4 CMSN:5282 was back on the bench in December 2025. The work was to actually calibrate the PTO in this receiver to <1kc EPE and ~1kc linearity. This was followed by a complete front end alignment. SN:5282 is "dead-on accurate" with great performance capabilities now. The receiver is tuned to Trenton Military 15.035mc USB VOLMET from Trenton, ON, CAN using the Collinear Array Ant - 1500hrs PST 12-20-25

1952 51J-3 - SN: 1999 -  Refurbishing, Servicing and Alignment

Many of the 51J-3 receivers that were shipped out of Collins Radio Company didn't have data plates to identify what type the receiver was. Identification of these "tag-less" 51J-3 receivers was originally by way of the Collins Manufacturing Serial Number that was punch-stamped on the rear of the chassis and ink-stamped on the front panel tied to the original 51J-3 manual and other paper-work that originally came with the receiver from Collins. Most of these receivers have long since lost their matching original manual and paper-work so unless one is familiar with the 51J-3 and the R-388 there isn't an easy way to actually identify what type of "tag-less" receiver they might have. Nowadays, identification has to use the very subtle physical differences between the R-388/URR receivers built between 1951 and late-1952, taking into account their "military" end-users and the civilian 51J-3 receivers built between 1951 and 1953. For these "tag-less" 51J-3 receivers, the PTO serial number is the most important "identifier" and gives positive indications of who the end-user originally was. Other subtle indications are also observed to help confirm the identification of a "tag-less" 51J-3.

The Ham & Hi-Fi Photo of SN:1999

On the downside,...the MC drum dial looked very faded and was barely readable,...at least in the photographs. The one questionable find was under the top cover where a schematic was glued with "R-388/URR" shown as the title.

I studied the photographs for several days,...in fact,...for several weeks. Finally, I had the opportunity to travel over to Sparks, so I called ahead and set up an appointment to stop by Ham & Hi-Fi. A deal was made and I took SN:1999 home with me. Nov 4, 2025

Authenticity Concerns - While SN:1999 has nearly all of the indications of being a genuine "tag-less" 51J-3, here are two observations.

1. The C.R. suffix on the PTO serial number implies that it came from a 51J-4 receiver. However, the wiring looks stock original but I suppose it's possible that a replacement PTO could have been installed professionally with all of the proper lacing - but by whom? Collins? If it's a mid-production 51J-4 PTO, where did it come from and who did this ultra-authentic installation? Would Collins perform a PTO replacement job and use a current production 51J-4 PTO? Photos below show the PTO and the wiring which looks Collins-authentic to me. Observation of the solder joints show they are top-quality work with the proper wraps and professional soldering but there doesn't appear to be any MFP on the four solder joints. All of the solder joints have the patina of age. Either this is the original PTO with a "C.R." suffix, or, the other possibility is that the PTO is from the time period of the mid-production 51J-4s and is a replacement installation that was performed by Collins. That would only have been done to a 51J-3 receiver, not to a R-388 receiver. I can't explain the "C.R." suffix but the installation just looks "too good" to be anything but original or a replacement that was installed by Collins (this is especially true of the PTO output cable-shield where it's soldered to chassis-grounding lugs - it's too good to be anything but Collins work.) UPDATE: Dec 21, 2025 - I performed a PTO calibration on SN:1999 so I had to dismount the PTO out of the receiver. This allowed a very close inspection of the soldering joints involved with the PTO installation. These soldering joints are excellent, top-quality work BUT they aren't original - at least, I'm about 90% convinced that this work, while not the original soldering, is so good that it had to have been done at Collins as part of a customer repair. The installation of the PTO is nearly perfect, but close inspection shows no MFP on the solder joints. Of course, the other indicator was the "C.R." suffix that never did seem to "fit" the time period. I now believe that PTO SN: 5487C.R. was installed around 1957 as a repair performed by Collins. Collins would have only done that type of work on a 51J-3 receiver, not on a R-388.
 
2. The R-388 schematic under the top cover and the pencil notation "R388#1999" under the top cover is a concern since it ties the serial number of the receiver to the top cover. But, it's not an original Collins pencil notation. It was written by someone at a much later date than 1953. However, there's really no way of knowing if the top cover is even original to the receiver. Of course, the contradicting notation on the inside of the bottom cover in black grease pencil "51J3 1999" just illustrates the resulting confusion that can happen if "unofficial notations" are weighed too heavily. Of course, having no schematic under the top cover is what would be expected. As far as this top cover goes, it's possible that the 51J-3 receiver sometime in the past was installed in a Collins "A" cabinet where the original top cover was removed (it shouldn't have been,...but it might have been.) Installed in a cabinet explains why there's so little "rack rash." Maybe later, removed from the cabinet for some reason and left with no top cover would explain the small oil spots on the chassis and the protective coating on the drum dial. The original top cover was almost certainly lost and this replacement was found and installed. The pencil notation was added at that time. A lot of speculation but one never knows exactly what happened 70+ years later.
 

Before chassis cleaning, note oil spots. This was after I wiped the white powder off the MC dial drum.

The tube shields appeared to have some oxidation but once I pulled one and examined it closely I could see that the coating was MFP. The heat generated by the tubes had turned the MFP color very dark so it looked like oxidation. The tube shields were just wiped down with Glass Plus to remove any dust or oil spots.

The back apron just needed a bit of Glass Plus and a small paint brush to clean the terminal strips. The two SO-239 connectors were also cleaned. Since the SO-239s are silver-plated, they are always oxidized and dark color but since silver oxide is conductive it doesn't matter.

The front panel didn't need cleaning, it was in immaculate condition. The bakelite bezel was dismounted so that the glass windows could be cleaned using Glass Plus (I ended up replacing the glass since the MC glass was chipped badly.) The knobs were all very nice so they were only dismounted, wiped down with Glass Plus, wiped with a cotton-flannel cloth and remounted. At this time, I didn't drop the front panel. I will do that if I find it's necessary later during test and alignment.

V102 - 6BE6 - 1st Mixer - 37/36 - At minimum acceptable

V105 - 6AK5 - Crystal Osc - 22/22 - At minimum acceptable

V106 - 6BE6 -  2nd Mixer - 24/36 - weak ~ 33% below minimum acceptable

V110 - 12AX7 - Det/AVC Rect - 20/42 and 15/42 - both triodes weak and ~ 50% below minimum acceptable

V111 - 12AU7 - AVC/IF Output - 60/52 and 100/52 - unbalanced for some reason. Replaced as a problem-preventive measure.

The other 13 tubes all tested significantly above (>50%) minimum acceptable.

None of the tubes were "bad" - that is, open heater, shorted or no emission - just weak, that is, being at or below minimum acceptable on the TV-7. Having all of the tubes being NOS or testing like NOS assures that the receiver will align correctly and perform well. Tube testers aren't the final word however. A Mutual Conductance tester, like the TV-7, will test the tube at 60hz and at voltages that aren't anything like how the receiver's tube circuit is designed. The tube working correctly in the receiver is the final test.

51J-3 SN:1999 Under the Chassis
Note that typical of the R-388 or 51J-3, the AC power cable exits the chassis above the fuse holder. These locations are reversed on the 51J-4.

Three-Wire AC Power Cord? - The three-wire power cable upgrade was performed on a lot of R-388 receivers, probably by military depots where the installation was first-class. I would think that a commercially used receiver that was maintained by professional technicians would also have had the power cable upgrade. I was all set to just use the "as-original" two-conductor power cable that was installed and just do the strain-relief installation. However, when I cut the power cable to start the installation, I found the cable was actually an 18-3, a three conductor power cable, that had the ground wire cut and was only using the hot and neutral wires. When I unsoldered the wires, I found that they had only been tack-soldered,...not even a wrap or anything,...just a glob of solder. So, the power cable installation was obviously a "hamster job." I decided at that point to do a professional installation as it would have been done to a R-388 at a military depot and use the three conductor cable, a Heyco 6P strain-relief and a vintage high-quality three pin (grounded) AC power plug. I don't know what to think about the "hamster" AC power cable installation. It was the only example of inferior workmanship I found in the receiver.

Initial Test - Nov 9, 2025 - At this point, SN:1999 was ready to have power applied. A 4Z loudspeaker was connected and I used my indoor W6VLP shielded-magnetic loop "test" antenna. The operational point where the B+ has come up but before the reception point had quite a bit of a noticeable hum level. That subsided as the receiver "came to life." But, the hum level was enough that it modulated any type of heterodyne. It was very noticeable with the CAL heterodyne. As far as reception, I tested 20M and heard many stations in CW and SSB. I tested XSQ on 16.874mc and it was coming in just audible. WWV 15mc ran the CL meter up to about +20db. The BFO was set up 180º out although it will work as set up. It's just the opposite of normal 51J set-up for the BFO. So, there's still some more work to do plus the front bezel glass is filthy, so that needs to be taken care of. Checked WWV 15mc using the Collinear Array antenna and the CL meter indicated +40db which is just about normal although a freshly-aligned 51J receiver will usually have WWV 15mc push the CL meter to over +50db using the Collinear Array.

Testing the Filter Capacitor - This receiver had been tested a Ham & Hi-Fi but it was just a quick test for functionality. Since the receiver had been powered up, the filter capacitor was probably already somewhat reformed. Or,...maybe not. The C measurement showed 45uf and 42uf. The 42uf seemed erratic. When in operation there is a noticeable hum that modulates the BFO heterodyne but otherwise is fairly low level. I have several spare filter multi-section capacitors. Hopefully, there's a good one in the group. I had to use a 45uf-45uf multi-section (for the R-390A.) These are physically the same size with the same connections but with a slightly higher capacitance per section. I used a 1958 date-code multi-section. This capacitor eliminated the hum problem. Or, maybe I just thought it did. The hum seems to come and go. More hum info further down in "Hum Problem."

Cleaning Bezel Glass -  I removed the dial bezel to clean the glass and found that the MC dial glass had a good size chip on one end. I had a perfect spare glass piece so it was cleaned and installed. I also replaced the KC dial glass with a perfect spare that was cleaned and then installed. All knobs were removed and cleaned, then reinstalled.

Run Time - Before the alignment, I like to operate the receiver for a couple of days. This gives the tubes time to get up to full emission (if possible) and for all of the components to have some run-time put on them to make sure everything is okay. I didn't replace any components except for the filter multi-section capacitor. All other components are original. Most of the time, with R-388 receivers, running on all original components is not too much of a problem. Nov 10, 2025

Hum Problem - This was a modulated hum. With no signal, no hum was heard through the loudspeaker. If a CW or SSB signal was tuned, there wasn't any hum because the RF Gain was greatly reduced for proper demodulation. The hum was affecting AM reception with the RF Gain at maximum. It didn't matter whether the AVC was on or off. The first step was to isolate where the hum originated. I used a function generator to input an audio frequency sine wave into the grid of V112 (1st AF amplifier.) The audio output at the loudspeaker was clean with no hum. That test eliminated the power supply as the source of the hum and also the audio output section of the receiver. Next, I input 500kc into the grid of V107 (1st IF amplifier.) I modulated the 500kc with a sine wave and the audio output at the loudspeaker was clean with no hum. This eliminated the 500kc IF as the source of the hum. Next, I switched on the Calibration Oscillator and tuned in that carrier (the Cal Osc is connected to the RF amplifier grid.) Now I had the hum. This meant that from the grid input on the 500kc IF through the rest of the IF, Detector and audio circuits, including the power supply of the receiver were operating correctly (well, didn't have any "hum" problem.) Therefore, the hum had to be in the front end of the receiver. Most likely one of the "tested" tubes had a slight leakage from the heater to the cathode,...not enough to show as a short on the tube tester but still enough to modulate the cathode with 60hz AC. I swapped some of the mixer tubes around and it seemed that the one 6BE6 that wasn't replaced might be the problem tube. One mixer tube is only used on Band 1 so I put the suspect tube in that location for now. It would be nice to have all NOS tubes in the front end, so I replaced all of the Mixers (three of them) with NOS tubes. This seemed to cure the problem. Or, did it? Still, the hum problem seemed to come and go,...sometimes there would be noticeable hum. Other times, clean and clear. See update at the end of this 51J-3 write-up.

The exceptional cosmetic condition (post-cleaning) can be seen in this photo. The plastic bag contains a spare fuse and lamp. These plastic bags were installed on both R-388 and 51J-3 from the factory and are almost always missing nowadays. The original alignment tools are almost always missing too.

Photo Details Showing Areas of Interest or Concern

PTO Serial Number

This is the primary identifier used since ALL early R-388 receivers used "M" prefix PTOs and civilian receivers, like the 51J-3 and 51J-4 used no prefixes or suffixes or used "C.R." suffixes on their PTOs. Collins started adding the "C.R." suffix to the civilian PTO around the time that the 51J-4 was introduced.  However, after a PTO calibration allowed a close inspection of the soldering, I'm convinced that this is a Collins repair installation.

PTO wiring lacing

This shows that the PTO installation in SN:1999 appears to be original to the receiver, note the lacing that appears to be as original. The wire wraps on the terminals are perfect and the soldering is at a professional level. This might be the original PTO but more likely it's a replacement that was installed by Collins as part of a customer repair.

"51J-3 1999" inside bottom cover

Written in black grease pencil, this is located on the inside of the bottom cover. It shows that someone else thought that SN:1999 was a 51J-3. Or, maybe they "knew" it was. Unofficial notations maybe interesting but can't be relied upon as accurate information.

Paint is still in Data Plate Screw Holes

This close-up of the Collins Mfg. SN and the data plate area of the front panel shows that the original paint is still inside the data plate mounting holes. This area of the receiver is very important because it's obvious that a data plate has never been mounted here. Normally, when a data plate was installed, the wrinkle finish paint near the screw holes will be compressed. This results in the paint around the screw holes looking "glossy." So, observing that the paint is still in the screw holes and the wrinkle finish hasn't been compressed, no data plate has ever been mounted to SN:1999 which indicates the receiver wasn't a R-388 when it left Collins.

Side Panels have no Mil-Stamps

This shows the area of the side panels where typically an "eagle" type of military inspection stamp is found. While the absence of mil-stamps isn't a positive identifier, since they can easily be washed off, the absence, when combined with other indicators, helps to confirm the civilian status of the receiver in question.

Anchor Ink-Stamp

A thorough inspection did turn up this Anchor ink-stamp, probably USN approval for the component itself. It's logical that since the same relay was used in both R-388s and 51J-3s, all of the Break-in relays were stocked with one part number. When a receiver was assembled, the parts were pulled from stock and, since the stamp was the result of a component test-inspection and approval they would end up in either R-388s or 51J-3 receivers. 

Anchor & Triangle Ink-Stamps

 I've seen these stamps on almost all R-388 CL meters. It's probably for the same reason that the Break-in relays have the mil-stamps. Since the R-388 and the 51J-3 use the exact same CL meter, all of the CL meters were stocked as one part number. The stamps are probably for component test-inspection and approval to allow Collins to put the meters into their stock "ready-to-use." The orange writing at the bottom of the meter is "SEALED DO NOT OPEN."

Under Top Cover - "R388#1119"

I found this pencil note under the top cover about where the center wing-nut notch is. An unexpected notation and one that adds slightly to the concerns about the correct identification of the receiver. Of course, it's not a Collins-official notation. It might have been an erroneous assumption made from referencing the schematic title. Unofficial notations maybe interesting but can't be relied upon as accurate information.

1. HP 3325A Synthesizer Function Generator (up to 20mc) providing fixed 500.000kc for IF alignment. This synthesizer can also increment frequency changes for checking crystal filter.

2. FNIRSI DPOS350P Synthesizer RF Signal Generator providing RF (up to 50mc.) This unit is also a two-channel oscilloscope, a frequency counter and a DVM. It also can provide limited spectrum analyzer functions and allows fully incremented adjustments for all functions. This unit could provide all test functions but the HP synthesizer I think is easier to use for the IF and Crystal Filter alignments (the large buttons on the HP 3325A are easier to "punch" than the screen menu access used on the DPOS350P.) The ME-26D VTVM is easier to use for the Diode Load measurements.

3. ME-26D - Military-HP VTVM allows an analog measurement of the Diode Load voltage for easily observing the "peak voltage" during alignment. Also, for the Crystal Oscillator adjustments the VTVM is easier to "see the peak" and then adjust to < -2vdc.

4. General Radio 1192-B Digital Frequency Counter for PTO and KC dial set up with shielded cable or 10X 'scope probe for isolation.

5. Original alignment tools provided with the receiver. The original tools make adjusting the IFs and the ceramic trimmer caps easy. Reproductions of the tools might be available.

Rear Chassis Apron "Line Inspection" Stamp

This isn't an "indicator" since these ink-stamps are sometimes also found on R-388 receivers. Over the years, most receivers have been "cleaned" extensively and these water-soluble ink inspection stamps seldom survived. This is one of the better examples I've seen. Sometimes the "Line Inspection" stamp will be located on one of the side panels, especially on later production.

Alignment Hints:
1. Use modern or fairly modern test equipment. Newer designed equipment is much easier to use, a lot more accurate and it reduces the total amount of test gear needed. A synthesizer RF generator eliminates the need for a digital frequency counter monitoring the generator's frequency. Just "punch in" the frequency and the amplitude and you're ready to go. More modern equipment will provide several types of test gear functions in one small package. Easy to use and accurate. In fact, where I used to have to take a receiver to the "test bench" for alignment, now I take one small, light weight test device to the receiver to perform the same task more accurately.

2. When connecting the IF transformer load the pins on the transformer involved will be pin 1 and pin 4. The 2pf coupling capacitor also connects between these two pins. With the receiver on its left side, looking at the IF transformer bottom, pin 1 is to the upper left and pin 4 is to the lower right. Make up the series 4.7K and 0.01uf cap with two flexible leads with small alligator clips to allow easy connecting. Since the RC detuning network always has one end connected to ground-chassis, that lead can stay in place. Then only the remaining lead can be moved to the required IF transformer pin. With pin 1 loaded you adjust the bottom IF trimmer. With pin 4 loaded you adjust the top IF trimmer. Move the load lead as instructed in the procedure. This method is just about as easy as it gets for the six "loaded" adjustments.   >>>

51J-3 SN:1999 with PTO SN: 5487C.R.

 
51J-3 SN:1999 in a Collins Official 51J cabinet

Post Alignment Performance - 500kc IF was pretty close, Vari-IF way off, RF way off, so alignment made a significant improvement in the receiver operation. Tracking is right-on at the center of the MC dial and skews out about 5kc at each end band which is no problem for the fiduciary to correct. WWV 15mc will push the CL meter to +40db (+55db after CL adjusted) using the Collinear Array. Tuned in Trenton Military 15.035mc USB. CW Chinese Maritime beacons XSQ on 16.879mc and 16.854mc. 20mc WWV was +40db, lots of 15M activity (contest going on.) Heard PS7MA on 15M CW out of Brazil.   Alignment completed on Nov 15, 2025.

And, don't forget like I did,...to adjust the Carrier Level meter. The meter adjustment was pretty far off and driving the meter to the negative side stop pin when the RF gain was at max with the AVC on. The meter adjustment pot is a little touchy so go slow. Once the narrow area of adjustment is found, it's easy to zero the CL meter. After adjusting the CL meter, now 10mc WWV runs the CL meter up to +55db. 15mc WWV is also going over +50db. 20mc WWV at +45db.

And, I also didn't adjust the CAL C-trimmer for the 100kc Crystal Calibration Oscillator. The CAL C-trimmer didn't have enough span for zero-beating WWV, so I had to adjust the ceramic trimmer on the chassis. I first set the CAL to mid-C and then adjusted the ceramic trimmer for zero-beat. I then "fine tuned" the heterodyne that results from WWV's carrier beating with the CAL oscillator by adjusting the CAL for less than a one cycle beat note, so the CALIBRATE is now right-on 100.000kc.

UPDATE: Nov 29, 2025 - I've had an empty but very nice Collins 51J cabinet just setting around here for quite a while. I'm not a fan of "cabinetizing" any of the 51J receivers because it adds to the overall weight. But, I really think that SN:1999 was in a cabinet originally, so I'm going to try the installation and see if I can become accustomed to the appearance. See the photo above,...  UPDATE: Dec 22, 2025 - SN:1999 was removed from the cabinet for calibration of the PTO. This allowed assessing if there were any advantages to having SN:1999 installed in the 51J cabinet. The cabinet just takes up too much room and adds too much weight. I've placed the 51J-3, sans cabinet, on top of the 32V-3 transmitter, slightly elevated to not block the V-3 vents.

UPDATE: Dec 21, 2025 - PTO Calibration - I've been having pretty good luck recalibrating 70E-15 "CR" PTOs, so I decided to go in and recalibrate this PTO. This involves some time consuming disassembly, like dismounting the front panel, dismounting a few components, all to be able to dismount the PTO but leaving the wires connected so the receiver can power up the PTO. I was very careful to preserve the lacing as I dismounted the PTO since this is one of the key indicators that either the PTO is original to the receiver or it's a Collins-installed replacement (I was able to slide the lacing up the wiring so the knots were maintained.) A quick test of the existing EPE and I got an incredible 15kc! I had tested it at 11.5kc a while back. Although this test that showed 15kc EPE it was just a "quickie" test so maybe not all that accurate. But, the upshot was that this PTO was in serious need of calibration. The first adjustment of L002 was one turn clockwise. That got the EPE down to about 5kc. The second adjustment was for about half a turn clockwise. That got the EPE down to about 3kc. One more half turn clockwise and the EPE was <1kc and the linearity deviation was <1kc, which is good enough. This PTO was a "C.R." type and I've had very good luck just using L002 adjustments on these later 70E-15 PTOs that I've found with the hex plug still coated with green Loctite (indicates that the PTO has never been tampered with.) Reassembly took a little more than one hour. I was able to slide the lacing back down the harness wires so that it appeared exactly like I'd never dismounted the PTO. I checked receiver performance and all was fine but I'm going to go through the Vari-IF alignment and the RF tracking again since there are slight changes there due to PTO calibration, especially the Vari-IF that is cal'd at the MC dial edges where the EPE might have made a slight difference in the alignment. 12-22-25 - As suspected, the Vari-IF was slightly off but the RF tracking was not affected since it is aligned at the center of the band where the PTO was accurate prior to calibration. Now, the PTO is accurate from band-edge to band-edge and performance is about as good as it's going to get,...and that's excellent.

The earlier 51J-1 and J-2 have desirable features like the great front-end selectivity and the very tight IF selectivity. Performance of these initial versions is impressive, with zero drift and 1kc dial accuracy, making it possible to still use a J-1 or J-2 in a vintage ham radio station set-up, even in vintage CW or SSB stations. But, finding a good condition, original example of a J-1 is next to impossible and even the J-2 is a very difficult find. I have a 51J-2 that required two J-2 receivers to make one complete, functional receiver. But, it's an amazing performer considering it's one of the early versions of the 51J Series. I've recently restored a 51J-1 and returned it to its original specs. All of the classic "51J characteristics" are present, even in this earliest version of the 51J Series. 

It's lucky for those amateurs and collectors who want to own and use potentially the best all around performer,...and they don't mind digging into (or maybe just putting up with) the infamous 70E-15 "M" PTO,...the military R-388/URR can provide the vintage military radio user with a great performer. A little wider IF bandwidth provides much better AM audio quality than the earlier 51J versions. Thousands and thousands were built in the early fifties - a time when vacuum tube design was peaking and the military demanded the very best radio gear. The R-388/URR is probably the easiest version of the 51J Series to find and they are usually the best bargain (I've owned many R-388s and have worked on many more,...although I only own one example now, they are excellent receivers.) The most difficult 51J to find is the 51J-3 but it's identical to the R-388 (excepting military acceptance stamps, data plate and PTO serial number) and performs just like the R-388 although the 51J-3's 70E-15 PTO might be in better condition since most J-3s weren't used 24/7 like the military R-388 (but don't hold your breath,...there's much more to the early 70E-15 problems than just 24/7 operation.)

The best communications equipment design and manufacturing company at the time, Collins Radio Company, provided a couple of "winners" in the 51J Series with the both the R-388/URR and the 51J-4. If you own a true civilian 51J-3, it's a rare one and will perform just like the R-388. And, of course, the 51J-1 and 51J-2 have their fans too (I'm one.) All 51J versions are receivers that are either at or fast approaching septuagenarian status, and yet, they are still easy to use for reliable communications "on the air" on any ham mil-rad net or any amateur AM-CW-SSB vintage radio net or for ultra-easy "band cruising" as a SWL receiver on any frequency range just listening for interesting signals (and there are a lot of those.)

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