[ARC5] Battery Tubes Experiment - AVR-20 vs. BC-474

[Mike Morrow]

Dave wrote:

> Suggested subs for an "ARC-5" experiment:
>
> 12SK7 - 1N5
> 12K8 - 1A7
> 12SR7 - 1H5 (silicon if second diode wanted
>              or 1H6 at slight derating for dual diode)
> 12A6 - 1A5 (if series fils) 1Q5 (if parr. fils)
>
> List of many of the battery types at:
>
> http://www.fourwater.com/files/batradio.txt


One of the best sets for which there is an indirectly-heated
filament version and a directly-heated version is the 1939 RCA
AVR-20 (and -20A and -20A-1), compared to the receiver in the
SCR-288 (BC-474).

1939 AVR-20 Manual:
  http://www.vmarsmanuals.co.uk/archive/969_RCA_AVR20_Aircraft_Communications_Receiver.pdf
 
SCR-288 Manual:
  http://www.greenradio.de/htm2/SCR288.pdf

--AVR-20                  --BC-474
RF         6S7            RF            1N5
MIXER/LO   6K8            MIXER/LO      1A7
IF/BFO     6F7            IF/BFO/AVC    3A8
DET/AVC/AF 6B8            DET/AF1, AF   1D8

I have always liked the AVR-20-series since I bought my
first one in 1967 for $1.  IMHO, it is one of the best
examples of that era (1939) for putting a reasonably
good receiver in a small box using only four tubes, and
still providing an RF stage, BFO, and AVC.

I wonder why a set similar to the SCR-288 was not used for
coastwatching stations.  The AWA 3BZ seems specifically
designed to be heavy, bulky, complex, and power hungry...
not at all something that one would want for such service.
AWA could have have copied the SCR-288 design and better
served the coastwatchers.

Mike / KK5F