[Milsurplus] Arc-38A as modified by RCA

Mon Nov 2 02:43:33 EST 2020

Mike
I do not agree with you that the ARC-21 had a history of unreliability.  It certainly was not much different then any other system found in the B-47 bomber other then the K Bombing and Navigation System.  This system weighed in at over a thousand pounds and used 370 vacuum tubes and an even higher number of relays.  MTBF for the BNS was so low that spare modules were carried in the B-47 Navigator's compartment.
It is rarely mentioned that the AN/ARC-21 was designed for use in the B-47 where it was mounted in the rear of the aircraft, aft of the rear landing gear, along with the ARC-27 UHF transceiver.  This location is where vibration and temperature extremes work it's magic.  Any HF transceivers used in place of the ARC-21 were installed in support aircraft such as the KC-97 or KC-135, not in a B-47.  No other HF transceiver available at this time was able to operate under the extreme conditions found in the B-47.  
The ARC-21 did have initial teething problems not unlike many other "state of the art" systems found in the B-47 or other aircraft.  But these problems were addressed and corrected as the source of the problems were determined and the failure mechanisms understood.  This was verified in the final report of "Project Big Eva" An Accelerated Service Test of Radio Set AN/ARC-21 in March, 1955.
There were two U.S. Congressional investigations concerning the ARC-21 of which I am aware.  The first was titled "Air Force Development and Procurement of the AN/ARC-21 Airborne Radio Transceivers," March 29, 1954.  The second was titled "Examination of the Pricing of the AN/ARC-21 Receiver-Transmitters," June 30, 1961.
The first investigation was about the Air Force procuring the ARC-21 before sufficient testing had been done on the prototype to verify performance.  The Air Force was in a panic with the build up of forces to fight the Korean War.  Congress was not critical of the problems facing the Air Force concerning the build up but they were concerned with the contracts let by the Air Force to RCA for an initial 3,900 sets and a follow on order for another 1,843 sets all before the delivery of the ARC-21 prototype for acceptance testing!  
The second investigation on pricing concerned the heat exchanger / pressure vessel which formed the outer case of the ARC-21.  This was the single costliest component of the ARC-21.  There was a $300 discrepancy between what RCA initially told the Air Force what it would cost and what RCA actually paid the contractor who made the heat exchanger.  Oh, well!
By the time of this first Congressional investigation, about 700 or so sets of the AN/ARC-21 had been delivered to the Air Force.  The problem with reliability was mainly due to vacuum tube and relay failures due to infant mortality and a lack of sufficient process control in the manufacturing of subminiature tubes and relays.  This is all well documented.  It should also be mentioned that there are approximately 100 relays used in the ARC-21.  The same number of relays are also used in the ARC-65.
There were also issues with other components such as resistors, capacitors and such but the main issue was with vacuum tubes and relays.  While the component manufacturers worked on improving their designs, overall reliability of the ARC-21 was improved with 100% component testing before module assembly.  This weeded out infant mortality failures of vacuum tubes and relays.  Completed ARC-21 sets then went through a 200 continuous hour operational test which included shake, rattle and roll while operating at elevated temperature.  Any failure found during the test returned the repaired ARC-21 to the beginning of the 200 hour test.  This forced the early failures and brought the reliability up to the point where the "Project Big Eva" testing program had verified that reliability was on par with other electronic systems used in the B-47.
With respect to your comments about the Navy choosing the ARC-38; perhaps you are not aware that the Navy had let a contract to Collins to develop the ARC-38 in 1952?  The Navy had also previously funded Collins for the development of the AN/ARC-26 AM transceiver.   The Navy issued this contract, worth a million dollars, in 1947.  It was cancelled when the prototype was evaluated in 1952.  The ARC-26 was the Navy's answer to the ARC-21 but evidently Collins had less luck with this design then RCA had had with the ARC-21.  The first Congressional investigation report also noted that Collins had commercialized much of the ARC-38, minus the SMO, in the form of the 618S-1.  What is common knowledge about the ARC-38 and the 618S-1 is not verified in the official record.
What caused the demise of the ARC-21 was the changeover from AM to SSB in the late 1950's and early 1960's.  As for the lack of reliability of the ARC-21 and the longevity of the ARC-65, it should be mentioned that they are practically the same radio.  Yes one is DSB and the other SSB but the change was accomplished without much of a redesign.  Both share better then 90% of the DNA of subminiature tubes and relays.  At least two modules are directly exchangeable between the two transceivers.  See the tube data below.  Bold type numbers are exclusive to that particular transceiver, all other tube types are also found in the other set.
ARC-21Type         Totals      Description:0A2           1 ea        150v VRT0B2           1 ea        108v VRT2E26          2 ea        10Wattpentode3B22          1 ea        Full Waverectifier3B28          4 ea        HV diode4-65A          4 ea        65Watttetrode5636A        16 ea        Dual Cont pentode5643A        1 ea        thyratron5670          1 ea        Twin diode5687          2 ea        Double triode5718          3 ea        Medium MU triode5719A        2 ea        triode5840A        14 ea        Sharp Cutoffpentode5896A        8 ea        Twin diode5899A        5 ea        Semi-Remote pentode5902A        3 ea        Beam pentode6021A        15 ea        Twin triode991            1 ea          58v VRTGrand total: 84 Tubes76 / 84 x 100 = 90.5% ofARC-21 tube types are also used in the ARC-65
ARC-65Type            Totals      Description:0B2             1 ea         108v VRT3B28            4 ea        HV diode4X250F        2 ea        PowerTetrode6CL6            2 ea        Power Pentode5636S        14 ea        Dual Cont pentode5636AS        2 ea        Dual Cont pentode5643S          1 ea        thyratron5670WA       1 ea        Twin diode5687              2 ea        Double triode5718S            3 ea        Medium MU triode5719S            1 ea        triode5840S            19ea      Sharp Cutoff pentode5896A            3 ea        Twin diode5896S            4 ea        Twin diode5899AS          6 ea        Semi-Remotepentode5902AS          2 ea        Beam pentode6021A            7 ea        Twin triode6021S            12 ea       Twin triode6021AS            1 ea        Twin triode991                    1 ea        58v VRTGrand total: 88 Tubes84 / 88 x 100 = 95.5% ofthe ARC-65 tube types are also used in the ARC-21
#yiv7963874434 -- filtered {}#yiv7963874434 filtered {}#yiv7963874434 filtered {}#yiv7963874434 p.yiv7963874434MsoNormal, #yiv7963874434 li.yiv7963874434MsoNormal, #yiv7963874434 div.yiv7963874434MsoNormal {margin:0in;font-size:11.0pt;font-family:sans-serif;}#yiv7963874434 span.yiv7963874434EmailStyle18 {font-family:sans-serif;color:windowtext;}#yiv7963874434 .yiv7963874434MsoChpDefault {font-size:10.0pt;}#yiv7963874434 filtered {}#yiv7963874434 div.yiv7963874434WordSection1 {}#yiv7963874434  The only difference beyond circuit changes for a balanced modulator, a linear PA, a narrow bandwidth mechanical filter, a product detector, and a higher accuracy Reference Oscillator is the type number suffix of tubes used in both sets.  As an example, the RCA preliminary ARC-21 manual called for a JAN 5840, the ARC-21 military manual, which covered the improved ARC-21, called for a 5840A and the ARC-65 manual calls for a 5840S.  The only real difference between these three vacuum tubes is the level of testing done after the tube was manufactured.  Like Papa John says:  Better ingredients, better pizza!
Regards,Jim

  From: milsurplus-bounces at mailman.qth.net <milsurplus-bounces at mailman.qth.net> On Behalf Of Mike Morrow
Sent: Thursday, October 29, 2020 6:59 AM
To: milsurplus at mailman.qth.net
Subject: Re: [Milsurplus] Arc-38A as modified by RCA  It's interesting that the principle post-WWII aircraft HF-AM set selected by the USAF was the RT-128A/ARC-21 along with the R-224/ARR-36 aux receiver.  This RCA-made equipment had a very troubled history of of unreliability and extreme procurement costs that prompted U.S. Congressional investigation.  The extended delays for introduction of this equipment caused the WWII-vintage AN/ARC-8 (T-47A/ART-13 and BC-348-*) to be continued in service and for USAF purchases of many Collins 618S-1 sets to fill in for the missing AN/ARC-21.  During the same period, the USN chose the Collins RT-311/ARC-38 and R-648/ARR-41 aux receiver to replace its AN/ARC-25 (T-47/ART-13 and R-105A/ARR-15).  From its introduction this Collins equipment was far more reliable and cost a small fraction of the USAF's RCA gear.  When SSB became the desired mode, RCA developed a USB conversion of the RT-128A/ARC-21 into the RT-400/ARC-65.  It appears RCA saw a similar opportunity and developed the  USB conversion of the RT-311/ARC-38 into the RT-594/ARC-38A.  Although very complex, apparently the RT-594 was successful enough to remain flying for another decade and more.  Older USN aircraft with the AN/ARC-38A often retained it after an RT-648/ARC-94 (Collins 618T-2) was installed.  It would be interesting to know if RCA used the same team to develop both the RT-400 and RT-594.  All things considered, I'd say they were very successful in military service.   Mike / KK5F
-----Original Message----- 
From: Ulrich N Fierz via Milsurplus 
Sent: Oct 29, 2020 3:53 AM 

Good morning Ray  here I have a 618S-1 (no original control head) and a long time considered the ARC-38A, but I think I can easily confirm: the A is a nightmare...   Good luck with your many radios  Ulrich  hb9aik - vk2ani  Ulrich Fierz8044 Zurich/Switzerland

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