Hi Jim,

<snip>

A question just popped into mind while writing this: During prototype
testing just why didn't Collins engineers understand and take measures
to mitigate the fact the audio deck gets roasted in hot SIGINT locations
(deserts, etc.), for example?

The Collins designers did understand the heat issues and early on challenged the specification and made suggestions. Some of the challanged specifications were addressed and others were not. See the R-389-390-final-engineering-report-(Al-Tirevold) which is enclosed. On document page 7, pdf page 12 starting at the second to last paragraph.

During development they probably at least placed units into
environmental overs in their labs to run them at the upper limits of the
temperature specification. That potential for thermal damage would have
been easy to catch. Or did the designers plow through the Design Phase
piece of the schedule thus not leaving time in the test-and-rework
schedule for engineering changes after that prototype analyses which
would prevent the RX (or, at minimum, a couple of its internal modules)
from simply becoming expensive 'throw-away' item(s) once damaged beyond practical repair.

Collins agreed to the requirements of the R-389 and R-390 in Military Specification Mil-R-13947A SigC dated 14 February 1958. This was later amended for the R-390A and became Mil-R-13947B SigC dated 26 October 1960. This amended specification for the R-390A/URR is also enclosed.

Spec is spec as they say so once the contract is signed Collins agreed to all of the contract requirements. Through the progress reporting cycles, the problems encountered in trying to make the agreed upon performance can be negotiated but there is no guarantee that the Signal Corps will modify the spec to make life easier for the Collins design team.

A case in point (no pun intended) is the waterproof case mentioned in the first answer, above. The high heat load of the R-390 in mobile configuration was addressed and the result was a new contract for the R-392. I am sure that there were many issues that were mentioned in the series of progress reports, some were changed and some were not.

The regulated power supply is mentioned in the enclosed Final Engineering Report on document page 14, PDF page 19. It appears that the regulated power supply was an agreed upon solution but since I haven't seen the first Military Specification, Mil-R-13947A, I do not know if it was required by the Signal Corps or suggested by Collins. In either case, the two parties agreed to it.

All of the above answers implies that the designer of the R-390 was the Signal Corps and Collins implemented this design. Of course this is just my opinion (I am sure that there will be some later comments) but Collins did manufacturer a receiver that was ahead of it's time for the U.S. Navy, the ARR-15. This is the first receiver using the second and third PTOs that Collins designed, patented and built.

I can easily imagine that the Signal Corps tested the R-390 concept by putting a crystal controlled pre-selector ahead of the ARR-15. Then you have an RF stage, mixer, variable IF, second mixer, fixed IF, then audio and power supply. This is pretty much the simplified block diagram of the R-390, is it not?

The early R-390/URR manuals (TM 11-856, January 1955 and two slightly
earlier Collins-published preliminary manuals) specify a 55C (131F)
upper environmental limit suggesting not just for storage but for actual
operation. No distinction made between storage and operation.

Whew! Can you imagine the temps found in a rack full of these units,
possibly with covers left in place, in a small SIGINT enclosure or
vehicle setting in a Middle East or North African desert back in the
day? Prototype testing should have raised that risk. But maybe, back in
the early 50s once the Korean Conflict erupted, the WWII mindset of
literally "Get it done at any cost!" could have still been in practice?
The later manual (TM 11-5820-357-10, R-390A/URR Operators Manual,
29DEC60) has that info left out for some reason. The bean counters
evidently caught on to that mindset I had mentioned and launched a
project which begat the cost-reduced R-390A in the mid-50s.

Well there is something to be said about the Korean War and how it affected military procurement. The B-47 was greatly affected and so were all of the systems that went into this aircraft. I feel that both the Signal Corps and Collins learned much from the R-390 development experience and the follow on contract for the R-390A cost reduction program reflects this Korean War experience and the trust in the Collins engineering department.

Regards,

Jim