[ARC5] ARC-5 and SCR-274-N IF Transformers

[Mike Hanz]

On 4/16/2014 3:46 PM, D. Platt wrote:
> As if everyone hasn't seen enough on this subject already... Ted, 
> W3PWW and I have been kibitzing on the phone and comparing schematics, 
> mechanical drawings, and such and appear to have determined that, 
> indeed, the Navy used dual-tapped transformers in the 2nd and 3rd 
> IFs.  Also, according late manuals, there may also be differences for 
> sets manufactured after 1945.  It may be well that each set should 
> retain its original transformers, although as I mentioned yesterday, I 
> know I've crossed over with no noted issues.  Now.. on another tack, I 
> said I thought one could probably modify the 40 meter (6.9.1 MHz) 
> receivers in the same manner as the 80 meters receivers.  Looks like 
> that's not the case.  Looking at the various mechanical drawings, the 
> SCR-274-N receivers appear to have a one-piece coil form, and are not 
> eligible for the mod, as written.  The Navy units, on the other hand, 
> look like they still have the split coils and ceramic spacers.  Ted's 
> having a look at his 40 meter receivers to see what's the real story.  
> The thing is, why would the manufacturers use a different methodology 
> for the two services?  Makes no sense, to me.  If anyone else has any 
> info, it would be good to know what you've found out.  At least the 80 
> meter rigs are good to go.

In Bell Labs' tome on its history, there is a segment dedicated to their 
stepping in with Western Electric to save the Aircraft Radio Corporation 
(described as "a small radio company that did not have the capabilities 
for large scale production") in producing enough SCR-274N sets for the 
USAAC/USAAF.  They accomplished this, among other changes, by improving 
manufacturing techniques and specifications for large scale 
manufacture.  That would indicate to me that otherwise identical part 
numbers for Western Electric versus ARC and its subcontractors might not 
always be identical in construction, though they may be interchangeable 
from a functionality standpoint.  I don't believe WECO was involved in 
the ARA/ATA or AN/ARC-5 HF systems, which would make those sets more 
identical with respect to their innards, even if produced by Stromberg 
Carlson et al.

     73,
  - Mike