[Milsurplus] RT-128/ARC-21 vs RT-311/ARC-38

Mon Mar 21 15:21:07 EDT 2016

The ARC-21 is another of the radio s that I have wanted to come across, thought they were extinct but have learned of at least two that are in existence as opposed the ARC-21 and 65 that are located at museums. The ARC-38/RT311 is almost the same only in a smaller case and better reliability but looking at the SSB conversion of the ARC-38 to the 38A and what a hack job that is would speculate that affects its reliability and just how long they were in service lacking any form of clarifier or fine tuning? Something that can be an issue in SSB but never a problem in AM. The conversions of AM transceivers  to SSB must have been expensive and I wonder just how long the converted radios stayed in service? How long was it between the mass conversion of the ARC-21 and 38 sets to the interdiction of the 618T family of radios?

Ray F/KA3EKH

From: Milsurplus [mailto:milsurplus-bounces at mailman.qth.net] On Behalf Of antqradio at sbcglobal.net
Sent: Monday, March 21, 2016 1:59 PM
To: milsurplus at mailman.qth.net
Subject: [Milsurplus] RT-128/ARC-21 vs RT-311/ARC-38

OK, I can start this thread with what information on the ARC-21 that I have researched over the last few years.  Any input that the group can provide on the ARC-21 or any of the contemporary comm systems will be appreciated.

The ARC-21 was originally designed for use in the B-47 which is the first aircraft to be designated as a "Weapons System."  With the development of this bomber, using the inefficient jet engines available to the US after WW2, there was little room in the airframe for equipment so most avionics were distributed through the aircraft, as space permitted.  Any space that wasn't pressurized for the three man crew was used for either fuel storage or bomb load.  This put the HF and UHF transceivers in the aft area of the aircraft about where the vertical stabilizer transitions from the airframe body. This is the reason that the ARC-21 is in a pressure vessel similar to that used by the ARC-27.

Using approximately 84 vacuum tubes and zero semiconductors, this system was by no means the largest avionics system used in the B-47.  This honor goes to the Bombing and Navigation System which has a tube count of approximately 300 and a correspondingly low mean time to failure rate of just a bit longer then the B-47 mission flight time.  The low reliability of the avionics systems used in this aircraft led to the big push to develop more reliable components and systems and, as a consequence, most of the Mil-Specs that came after the early 1950's.

RT-128 P/O AN/ARC-21; 2-24mc AM transceiver, 100 watts output, double conversion, triple when in CW mode.
> First airborne automatically tuned HF radio and eliminated the need for a radio operator.
> First airborne frequency synthesized radio capable of 44,000 frequencies in 500 cycle steps.
> First use of mechanical filters in a production radio, military or civilian.
> First radio to use a fully automatic antenna tuner, developed by ERA, Remington Rand, Inc.
> First radio transceiver able to operate at full transmit power up to 50,000 feet.

> Development contract date: 19 March 1948
> First production contract: AF33(038)-18325,  Date: 1952,  Quantity built: 3900, Unit cost: $15,372.77
> Second production contract: AF33(600)-32331  Date: 1956,  Quantity built: 121, Unit cost: $13,231.24
> Third production contract: AF33(600)-32926  Date: 1956,  Quantity built: 380, Unit cost $12,039.95
> Forth production contract: AF33(600)-33883,  Date: 1956, Quantity built: 551, Unit cost $11,599.00
> Fifth production contract: AF33(600)-35867, Date: 1957. Quantity built: 442, Unit cost $11,288.82
>
> Total built as of 20 April 1961: 5,349 units

Regards,
Jim
PS, yes, cats do appear to be fluffier.
________________________________
From: Mike Morrow <kk5f at earthlink.net<mailto:kk5f at earthlink.net>>
To: milsurplus at mailman.qth.net<mailto:milsurplus at mailman.qth.net>
Cc: arc5 at mailman.qth.net<mailto:arc5 at mailman.qth.net>
Sent: Monday, March 21, 2016 10:29 AM
Subject: Re: [Milsurplus] R-648/ARR-41 vs. R-224/ARR-36

Jim wrote:

> Hard to compare the above other then they both seem to be
> afterthoughts as system requirements were expanded.  Not to
>  mention that each were used by competing branches of the
> military; were designed by competing companies which both
> seem to have loyal followers.  Might as well compare dogs
> to cats.  ;-))

Jim, everything you list is **exactly** why they invite comparison!

END GOAL:  A Top-line MF/HF Main Set RT and Aux Receiver

It is fascinating to study what resulted as affected by:
USAF Requirements vs. USN Requirements
RCA Design vs. Collins Design

RT-128A/ARC-21 with R-224/ARR-36 vs. RT-311/ARC-38 with R-648/ARR-41

There was some common ground with the USB conversions of the RT units, since the USB designs for both the AN/ARC-21 and the AN/ARC-38 were done by RCA;

RT-400/ARC-65 vs. RT-594/ARC-38A

I am unaware of any other group of sets that present as much interesting parallel-path comparisons.  A few other "parallel" service-specific sets just don't come near:

HF
AN/ARC-8 (USAAF) - AN/ARR-11 (BC-348-A) and AN/ART-13A
AN/ARC-25 (USN) - AN/ARR-15 and AN/ART-13

VHF
AN/ARC-1 (USN)
AN/ARC-3 (USAAF)

Anyone with much interest in the past 80 years of vacuum-tube US aircraft communications receivers should have or study these:

AN/ARR-11 - BC-348-Q, -R
AN/ARR-15 - R-105A
AN/ARR-41 - R-648

The AN/ARR-36 is not on the list.  It is just too rare.  Aside from that, it would be a bear to use.  Its also significantly larger and heavier than listed receivers.

Mike / KK5F

      From: Mike Morrow <kk5f at earthlink.net<mailto:kk5f at earthlink.net>>
To: milsurplus at mailman.qth.net<mailto:milsurplus at mailman.qth.net>
Sent: Monday, March 21, 2016 1:55 AM
Subject: Re: [Milsurplus] R-648/ARR-41

> ... i am looking at the ARR-41 with changed feeling now. This was
> the final “NO” vote.

That would be a decision without sound basis, IMHO.

The R-648/ARR-41 represents the ultimate level of development for military LF/MF/HF aircraft receivers of the vacuum tube era.  snipThe USAF also used their contemporary RT-128A/ARC-21 (and RT-400/ARC-65) aircraft HF set with a R-224/ARR-36 auxilary receiver.  It uses the same model control box as the RT-128A, which requires frequency entry by setting pins on a drum.  I have an R-224, but it could serve little real purpose to try to get running.  The AN/ARR-41 has this closest competitor beat.

Mike / KK5F
PS:  The only significant cat vs. dog difference...cats are fluffier.
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