Ray
If we are to compare Collins to RCA radios then it should be the R-390 (non-A) to the SRR-13.  Both are contemporary designs with contract dates close to each other.  The contract date for the SRR-13 is 31 August 1950 as mentioned in the NAVSHIPS 91875 while the R-390 contract is 14214-PH-51-93 as shown on the nomenclature tag.  There are also specifications for each which predate the contract dates but I have only found the specification date for the R-390 which is 28 August 1950.

I have no idea of actual delivery dates for either the SRR-13 or the R-390 or when each actually entered inventory.  It appears that the SRR-13 was in use before the R-390 since the SRR-13 aka R-441 is listed in JANAP-161 dated 29 May 1952 while the R-390 is not.  The R-388 is listed in JANAP-161 with a data sheet date of 22 January 1952.  

WRT the R-390A, it is more then just a cost reduction redesign.  The final progress report for the redesign mentions that: "The main task of the contract, then, was to reduce cost of the equipments and improve the reliability, accessibility and performance."  The report lists all of the issues investigated which are quite extensive.  So it is fair to say that the resulting "A" receiver is more then just a cost reduction program.  

The SRR-13 is by no means a perfect receiver, there was at least one extensive corrections made to the Navy manual, some 64 pages, with a few circuit changes which include substitutions for some subminiature tubes and replacing subminiature signal rectifiers with silicon diodes.

There is a reason that the R-390 is less favored then the R-390A by Collins radio collectors.  It has a more complicated mechanical design which was harder to adjust and maintain.  It even required a special "green gear" to lock the mechanism when it was serviced.  No need to mention the heat problems caused by the voltage regulator in addition to the power supply rectifiers.  This radio runs hot which affects reliability.

What you describe as "tricks" is just experience gained in servicing the receiver.  Same can be said for either as one becomes more familiar with that particular radio.  As for the subminiature tubes, they are perhaps the most rugged and reliable tubes produced up to the invention of the Nuvistor.  

Having worked on the KWT-6 aka URC-32, the only subminiature tube replaced that actually solved a problem had an open heater,  The other half dozen or so tubes I replaced did not solve the problem at hand.  It is interesting to note that quite a few failures are due to bad ferrite tuned inductors and transformers.  Go figure!

The 6X4 rectifiers in most of the SRR receivers were replaced by silicon to reduce heat inside the receiver but a quick look did not find the change order, perhaps Nick England can fill in this gap?  I believe the same change was made in the R-390 series of receivers, for the same reason.
Regards,
Jim


Logic: Method used to arrive at the wrong conclusion, with confidence.  Murphy


On Tuesday, July 23, 2024 at 08:29:19 AM CDT, Ray Fantini via Milsurplus <[email protected]> wrote:


Think the thing about the R-390A is that from a maintenance standpoint all the tubes are “off the shelf” and maybe with the exception of the stupid ballast tube and the two rectifiers easily obtainable. In the SRR the only common tube is the 6X4, got to drag out the soldering iron to change any of the others and how do you test them short of replacement? The IF decks in R-390 receivers suffer from the Black Beauty of Death capacitor thing but so what, they are easy to access and replace. Replacing components in those weird little assemblies on the SRR or testing them in circuit is just about imposable.

If anything is an issue in the R-390A its problems with not knowing the mechanical “Tricks” for assembly removal and mechanical alignment and having to repair damage other may have done. Almost every radio I have ever worked on did not need to be aligned unless someone gets in there and cranks on the it. The other issue today with the R-390A is they have a flock of crystals in the first converter assembly and it’s not uncommon for them to be out of tolerance or dead resulting in a dead band or two.

In that respect the SRR has a small advantage. 

Think my point is that from the early fifties and the first R-390, the release of the R-390A in 1954 over fifty-five thousand receivers were produced. Many stayed in active military service into the nineteen eighties, would speculate that unlike the SRR family of radios R-390A receivers were installed, operated alongside the SRR and remained in service long after the SRR was gone and forgotten.

As far as comments on the RA and RB family of huge heavy radios, I am not saying that they are bad radios, just that they are huge, heavy receivers and in today’s world most Hams worship at the altar of smaller lighter latest box on the block. Imagine you can wedge two hundred SDR receivers into the footprint of one RBC and it will still weigh less.

 

 

Ray F/KA3EKH

 

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