[ARC5] SCR-274-N Version "-E" Components

Tue Aug 16 14:32:45 EDT 2016

Jay,
I have seen many SCR-274N component units with decals, most being B versions -- receivers, transmitters, modulators, and antenna relays.  I may even have a transmitter control box with a decal tag.  My theory is that use of decals eliminated "critical materials."
Also I have seen numerous BC-348 dynamotors with decals, plus a couple of DM-34 or DM-36 dynamotors for the BC-603/683 tank receivers with them.  So it was not limited to the SCR-274N.
US Army training schools sometimes used early models of equipment -- and this could have either been items never used in actual field deployment, or supplemented by later production versions -- as training items.  Examples found in my Dad's WW2 Fort Monmouth Signal School books are BC-312/342 B, C, D and BC-191 A, B, C, D.  The early BC-312/342 receivers included slightly different circuitry, a couple of the models having a unique Jones Noise Balancer in the antenna input which was deleted in later production; either not that effective in practice or too tricky to use.  Early BC-191 transmitters had tuning units with two binding posts on the front panel which were used in neutralizing the transmitter (yes, these were production components), also deleted in later production.  The Fort Monmouth books also describe the BC-610-A, B and C versions which were early production.
These books are from mid to late 1943.
My Dad's airborne radar training manuals from Camp Murphy, FL cover the airborne LORAN gear which later became the AN/APN-4 in actual service.  However, the models used in training had BC-number components and an SCR-number for the complete system.  The receivers covered not only the 1.7-2 mc range, but also frequencies in (IIRC) the 8-11 mc range; the higher frequency ranges were soon found to be unsuitable because of skip propagation and the SCR-system was only used in training.  Although, the SCR version might have been found in very early model B-29s, as they were the a/c that my Dad was training to work on.  He ended up being sent to the CBI and didn't get much chance to do so; he ended up working mostly on night fighters like the P-61 and P-70 as well as flying the Hump in transports as a radio operator.
There are two RCAF Command Set transmitters in my Junque (not, I emphasize, "junk"), both BC-459s, which don't have any obvious differences from USAAF versions.  So far I haven't seen one of the RCAF receivers, but would like to find one.
As for the decal seen on the eBay unit, it looked 99.99999% like an E.  As mentioned, I have two BC-456 modulators which are definitely E versions; so I feel like my call on that one is correct.
Hope this helps.
73
Mike
WA4DLF

      From: Jay Coward via ARC5 <arc5 at mailman.qth.net>
 To: kk5f at arrl.net; arc5 at mailman.qth.net 
 Sent: Monday, August 15, 2016 9:52 PM
 Subject: Re: [ARC5] SCR-274-N Version "-E" Components

 Mike, Were there any SCR-274N receivers, transmitters, modulators, antenna relays that had decals instead of nomenclature plates? I've seen many racks and shock mounts and dynamotors with decals and a damaged decal can easily change a "B" to an "E" or  even "F".  Training schools often used obsolete gear for the trainees to refurbish to acceptable working condition. This may be where a typo could change the true record if the equipment was returned to government inventory. But I have not heard why the RCAF receivers were designated "-B". Were all "-B" receivers built/rebuilt with molded caps? Or, does a refit/rebuild not change the revision letter as long as "form, fit, or function does not change? So far, only audio output impedance change capability drives the "-B' rev change. Where I work there is a constant "growse" about how much change in a released product requires a CCN (configuration control number) change. Should the US and RCAF units be treated differently? Your mastery of this subject matter is most commendable. I hope you plan a book. Regards,                Jay KE6PPF      -----Original Message-----
From: Mike Morrow <kk5f at earthlink.net>
To: arc5 <arc5 at mailman.qth.net>
Sent: Mon, Aug 15, 2016 4:45 pm
Subject: [ARC5] SCR-274-N Version "-E" Components

> There was a BC-454-E shown on eBay last week.
> I have two BC-456-E modulators.

I have seen these version "-E" components...I have a couple.

I am not aware *any* difference between them and the "-B" versions. I've seen mention of only the "BC-456-E" in official documentation (12R2-3SCR274-1 Operating Instructions, 25 JUL 56, IIRC) in a passing reference without any significance or explanation, crudely typed in.

I believe the "-E" marking is specious...most likely an error of some sort where a "-B" should have been. The -E models are identical to the -B models, from what I know. But I'd love to find out something different.

Mike / KK5F
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