[ARC5] Need Information

[Mike Morrow]

Floyd Petri wrote:

> Is it true that this non-compatibility if any is due to the plug on the
> back of the radios being different?

That's merely a consequence of the significant re-design of the original
ATA transmitters for the AN/ARC-5 system...SCR-274-N and AN/ARC-5
transmitter components are electrically different, so they should have
different connectors!

The SCR-274-N system is the Army's 1941 reduced-scope (only four receivers
and four transmitters) version of the original Navy ARA/ATA system (five
receivers and five transmitters).  All of the equivalent components of
these two systems are electrically and mechanically identical, except
for AF impedance.  The ARA/ATA set uses 300-ohm nominal AF impedance in
the receiver and modulator circuits, while the SCR-274-N using "-A"
version receivers and modulator use 4000-ohm nominal AF impedance.  The
version "-B" and later components can be internally wired for either
4000-ohm or 300-ohm.  Other than that, the ARA/ATA and the SCR-274-N
are completely interchangeable.

The original 1940 ARA/ATA and the 1943 AN/ARC-5 sets are both US Navy sets.
The AN/ARC-5 maintenance instructions state that *receivers* of the ARA
and the AN/ARC-5 can be used interchangeably as a unit...no harm or
significant problem results.  An ARA receiver in an AN/ARC-5 rack would
not serve well in the stabilized lock-tuned configuration that was the
predominant mode of use for the AN/ARC-5, but at least no smoke would
be generated.  ARA units lack the lock-tuned tuning port cover/wrench
that was standard on the R-25, -26, and -27/ARC-5 communications receivers,
so perhaps that helped to discourage the installation of an ARA receiver
in any AN/ARC-5 lock-tune installation.

The ATA and the AN/ARC-5 *transmitter* systems, however are rather different
electrically.  There are only *two* components of the ATA and the AN/ARC-5
transmitter systems that are *electrically* interchangeable, even if all
equivalent transmitter components used the same connectors (which they do
not).  Those two components are are the CBY/CCT-29125 and RE-2/ARC-5 antenna
relays, and the CBY/CCT-21626 and DY-8/ARC-5 modulator dynamotors.  That's
it...the complete list!  Since the SCR-274-N is essentially identical to
the ARA/ATA, so likewise only the BC-442-* and RE-2/ARC-5 or the DM-33-A
and DY-8/ARC-5 are interchangeable between the SCR-274-N and AN/ARC-5
transmitter systems.

The connectors of the AN/ARC-5 transmitter system were made incompatible
with the equivalent connectors of the ATA transmitter system for only *one*
reason, I believe:  To prevent installing an ATA component in the AN/ARC-5
system, and the reverse.

The ARA/ATA system and the AN/ARC-5 system co-existed together in the
USN from the introduction of the AN/ARC-5 in 1943, through the rest of
WWII.  New ARA and ATA components were ordered for replacement purposes
in existing installations for long after the AN/ARC-5 had become available.
Imagine the difficulty of preventing sailors-techs from once in a while
installing the incorrect but visually very similar component in the wrong
system, had that been made mechanically possible by using the same
connectors on both the ATA and the AN/ARC-5 equivalents components.

Connector rarity is one of several things that make the SCR-274-N system
far far far easier and much less expensive to assemble today, compared
to the AN/ARC-5 (connectors and mounts) and the ARA/ATA (mounts and racks).

> Is it true that ARC5 equipment is always black and SCR-274N equipment
> is always unpainted aluminum?

The VHF R-28/ARC-5 and T-23 or T-126/ARC-5 are, of course, always bare
aluminum.  These were made by Western Electric, the same people who
introduced the bare aluminum finish of most of the SCR-274-N. 

You may find some of the information at http://en.wikipedia.org/wiki/ARC-5
to be interesting.as well.  There are also links there to manuals that
may be downloaded for the SCR-274-N and the AN/ARC-5 LF/MF/HF sets.

Mike / KK5F