These are some articles about the restoring process of my unit, posted to the BA list.
Well, this is the first of a (short, don't worry ;-) ) series of articles about my progresses with my recently acquired R-388. Although mentioned in a previous message, I'll give again the basic data of this unit:
SIGNAL CORPS U.S. ARMY
Radio Receiver R-388/URR
Serial 109 Order 3362-Phila-52
COLLINS RADIO COMPANY
The serial number 6168 is stamped in the back panel.
The receiver is missing both covers, the metal piece which keeps the plugin cap and the rectifier tube on place and the tools (any spares around?). It has some 'extras' as the 354A-1 Mechanical Filter Conversion Kit (nice extra, with a 'bad' (read below) 1.4KHz, a good 3.1KHz and a 7.0KHz 'adaptable' filters) and two additional outputs at the rear panel, labeled 'diode load' and 'AGC'.
As I commented in my previous message, it has also some mods: V102 (first mixer) is now a 6DJ8 instead of a 6BE6, V114 (BFO) and V103 (normally 6BA6) are now 6AS6. I have docs for the V102 change and a similar (with a 6BE6) mod for V114. Later mod is not documented (any hint?).
At first glance, the receiver front panel is an 8+, so it needed little work (soft cleaning) to get it in very nice condition. MHz dial is a replaced one, in good condition, and KHz dial is snow white, in perfect condition.
First thing I did was to repair two broken ferrite cores (the only consequence of the shipping; not bad for UPS :-)); as they were broken at one end and I had some of the broken pieces, I could repair them without too much trouble. Anyway, I'm looking for spare ferrites (I need 6, as some other cores were previously repaired; any around?).
Next thing I did was to change the input voltage to 230 VAC, as here in Spain the standard is 220 VAC (a bit lower; good for filaments!). It was an easy task and need only the temporary removal of a cubic filter screews. Once the voltage change was done and after a visual check, the smoke test began... I knew the receiver worked some days ago, but travel from USA to Spain is long and, as you know, packets are not lovely managed so... ALL RIGHT!. In some seconds, the 'sshhhhhss' of the speaker revealed some activity inside the receiver... Not bad at all!. I had connected to the antenna connector a wire dipole for 40 and 80 meters and the 7 MHz band came up with good signals. I checked the SSB mod with a bit weak but good sound.
After some tweaking with the receiver, I find the first problem: some bands were dead. But not always the same!!. Time to put the receiver over its side... Well, when I touched the bandswitching mechanism, near the 'sandwich' contacts, the reception was intermitent... Some contact cleaner spray didn't solved it... After some work, I found that the person who did the 6DJ8 mod was not too good with the soldering iron... Some wire covers melted and not a clean work, as the rest of the mods: the failure was a big solder joint which was too near the chassis; when you moved the bandswitch, it could reach the chassis and the reception was lost. Once it was moved away, all the bands worked; but I plan to redo this previous job as I'm not satisfied with it.
Anyway, I began to note that, in the higher bands (from 15Mhz or so), the R-388 was not too sensitive... I did a fast (with the calibrator) RF alignment for higher bands and I got a bit better reception, but not as good as expected.
In parallel with all of these, I managed to open and repair a 1.4KHz mechanical filter which was sent with the unit as 'probably bad filter'. Yes, it was a 'real bad filter' as it arrived... With the helpful aid of John Kolb (thanks!), I opened the filter and found that one of the coils (I think it was the input coil) was out of its place; putting it on place with a bit of glue to prevent it getting loose again, restored the filter operation... yahooo!!!. I felt very well at that moment :-), you probably know why ($$$)!.
Next day, I toke the receiver and did a carefully cleaning of the chassis; it was in good shape, only some dust. The only elements which are corroded are the two transformer 'boxes'; the paint peeled in about a 30% of their surface. I wonder if this is usual... Then I lubed and cleaned all the gears. Now the dial knob has a bit better feeling... I really like it!.
As the receiver performance was not as expected, I decided to pull out all the tubes and check them in my Triplett 3444 transconductance tester. Second BIG surprise!. Two more tubes (apart of the three documented changes) were not the specified ones: V104 was a 6AU6 instead of a 6BA6 and V111 was a 5814A instead of a 12AU7. I _think_ these are not fair substitutions (any comment?) so i decided to look at my tube stock to replace them. And then the third BIGGER surprise!. Of the 19 checked tubes, 9 were weak!!!. And, the 'best' of all, the 6DJ8 which works as a double triode mixer in my unit was weak and the V106 (6BE6 mixer, premium quality 10M tube, with gold pins!) was weak AND leaking a lot in H-K and G1 tests... Perhaps this was the cause of some oscillations I found in the BC band... I was lucky enought to have spares for all the tubes (including 4 NIB Amperex 6DJ8 I bought in a cheap 400+ tube lot some months ago!) so I could replace all of them with good ones.
After the tube replacement, I went through an RF alignment with the calibrator, as suggested in the July 1991 issue of the Collins Collector's Magazine (devoted to the 51J-4; I highly recommend reading it). Now the receiver works better in all bands; only on 21MHz and upper bands I still detect a lower sensitivity than expected, but anycase, far better than before. I plan to continue working in this area.
Well, that's all for now!. Sorry for the long message... Please, if you have any comment / hint about R-388(A) alignment, let me know... this is my first R-388 :-)!
BTW, I plan to add soon an special section on the R-388 in my WEB page... stay tuned!.
Thanks and best regards.
Hi Larry and all the gang,
I am fortunate enought (thanks Ben!) to own a R-388 with the 354A-1 Mechanical Filter Conversion Kit (take a look at my WEB page, just below in the signature, for a bit more of information about my R-388) and a good collection of documents about it. As far as I know, the Filter Kit addition really converts the R-388 (51J-3) in a R-388A (51J-4); perhaps there are some minor differences (any hint, gang?), but the operation, alignment, knobs and appearance are the same, AFAIK. I think it should be very difficult to find an spare filter kit, but one never knows...
About information, I have a curious letter from Captain Paul Lee (W3JM), author of many articles about mods for the R-388, R-390A and other equipment. It is dated 3/11/69, and deals with the different 51J models. I plan to put its contents in my WEB page soon, as it is, from my point of view, very interesting. Mr. Lee wrote an interesting article in April 1961 CQ ('The Single Tube Product Detector'), based on a 51J-2 receiver, but useable on other receivers. One of the better years in the CQ magazine for articles of the R-388(A) is 1968... You have good articles about these receivers in April ('Further Improvements for the 51J', by Captain Paul Lee) and December issues ('More on Updated Improvements for the 51J Receivers', by Wilfred M. Scherer, W2AEF). I have a copy of all of them and are really useful.
Other very interesting resource is the July 1991 Collins Collector's Quarterly Magazine (volume 1, issue 1). It is titled 'Collins 51J-4 Technical Tips', but its contents is useful for the 51J-3 also. 20 pages devoted to all the relevant aspect of the receiver and its alignment. Highly recommended!.
Do you need more information?. Then go to the SAMS Photofact SET 260, FOLDER 6 (dated 12-54), called 'Collins model 51J-3'... Content is obvious ;-)
Of course, the TM 11-854/TO 16-35R-388-5 ('Radio Receiver R-388/URR'), dated 1952, is perhaps the mother of all documents about this receiver, but, as is so complete, sometimes is harder to find the needed information than in other documents. But it is all there!.
Please, I would like to hear of other articles and documents about this fine receiver. I like it a lot and enjoy using it!.