[ARC5] Differences: plain models vs "B" models.

[WA5CAB--- via ARC5]

At least according to the final manual (Revised 07/25/56), the only circuit 
differences between the -A and -B models of receivers and modulators is 
that the -A model audio transformers only match Hi-Z headsets. The -B models 
have a 250 ohm tap to handle 500/600 ohm audio loads. Note that the notes on 
the schematics are a little misleading in that they say something like "for 
use with 8000 ohm (or 600 ohm) headsets". That's correct but the actual or 
nominal transformer output is 4000 ohms (or 250 ohms) at 1 KC which matches 
from one to four 8000 (or 500/600) ohm loads with no more than a 2:1 mismatch.

The other difference between the -A and -B model receivers and transmitters 
is that all -A are black wrinkle finish and most -B are clear matte anodize 
(except in the modulators where for some reason the -E model is the 
unpainted one. According to various sources, dropping the paint was supposed to 
save weight and/or save cost. AFAIK, dropping the paint was a WECo idea.

Of the accessories, receiver racks, transmitter racks and antenna relay 
units dropped the paint. I've never seen an originally unpainted dynamotor, 
shock mount or control box. 

Robert Downs - Houston
wa5cab dot com (Web Store)
MVPA 9480