[ARC5] Re: [Milsurplus] SCR-274-N Transmitter Dial Accuracy

[J Forster]

This might have been a case of incomplete specifications. It is essentially
impossible to specify every parameter of many parts, so just those critical to
typical applications are usually specified.

Also, early in WW II, radio was almost as much of an art as a science. It took
places like the Radiation Lab to really put electronics on a sound engineering
footing. The people setting up the tube lines may also not have known the
application because of secrecy or bureaucratic isolation.

Even today, a transistor manufactured to meet the specs for a 2Nxxxx by different
manufacturers may have a totally different die design. Microprocessors  can have
undocumented instructions, and clever (= stupid) programmers build them into their
code. Then it all hits the fan when a vendor is changed and the undocumented
instruction does not work any more.

Also, back then there was not Automated Test Equipment, so few parameters beyond Gm
and gas were likely routinely tested on production lines.

As to the 150,000 tubes in stock, remember this was wartime and there were
shortages. Someone may have (quite reasonably, but short sightedly in hindsight) to
modify a coil or two by removing some turns, rather than scrap all that stuff.

Remember, these radios were like the cell phones of today and were not expected to
survive very long, because the planes would crash or get shot down. In fact, as has
been pointed out elsewhere, the few NOS/NIB radios we see today, likely never saw
service, let alone combat.

FWIW,
-John

===============

John Hutchins wrote:

> Michael -
> This peice of information should wind up on the Wikipedia!
>
> http://en.wikipedia.org/wiki/ARC-5
>
> Info Michael Tauson wrote:
>
> That collaboration had its own problems where WE
> couldn't follow basic instructions.  A.R.C. specified Sylvania &
> Raytheon Type 78 tubes due to the interelectrode capacitance.  For the
> first 5000 receivers, WE used RCA tubes which did not pass spec (even
> though they managed to slide past Navy inspection) due to several
> issues, including higher capacitance.  To correct for this, WE
> modified the coil assemblies which caused them to no longer work with
> other RU receivers.
>
> A.R.C. called a meeting with WE and the Navy about this problem in
> 1943.  At the time, WE had 150,000 Sylvania 78s on hand so they were
> ordered to build the coils sets for the receivers using them according
> to the original design and the not get creative anymore.  This also
> resulted in a change of the designation for the affected coil sets.
>
> Hutch