[Milsurplus] SCR-274N

[Mike Morrow]

Andy wrote:

> I am trying to complete a SCR-274N or ARC-5 setup but am having
> trouble getting the last few pieces i need, i need a 2 or 3 unit
> transmitter rack as well as the control for it and the 2 connectors.

Andy,

The most important thing to decide is whether you are completing a
SCR-274-N set or an AN/ARC-5 set.  You can't mix and match components
in the transmitter system of these sets.

There is NO transmitter system *electrical* component of the SCR-274-N
that is compatible with the equivalent component in the AN/ARC-5
transmitter system EXCEPT the dynamotor and the antenna relay.

You can NOT put AN/ARC-5 transmitters in SCR-274-N racks, or vice versa,
without damaging the rack or transmitter connectors.  The connectors
are NOT mechanically the same, nor are they wired the same.  The MD-7
modulator can NOT be used with SCR-274-N transmitters and vice versa.
The transmitter control boxes can NOT be swapped.  The 12- and 18-pin
connectors from the modulator to the rack and control box are not the
same between the SCR-274-N and the AN/ARC-5.  For transmitters, you 
can't mix and match components of these systems at all, except the two 
components I've mentioned.

The AN/ARC-5 transmitter system has significant differences (improvements)
compared to the ATA and SCR-274-N.  In the WWII Navy, it was not unlikely
to find both the ARA/ATA and the AN/ARC-5 in service at the same time and
location.  The connector differences were a deliberate part of the program
to ensure that components from one system were incapable of being used in
the wrong system.  The receiver situation is different.  Those had no
gross differences that would cause harm if one were placed in the rack for
a different command set.  Receivers from the earlier RAT-1, RAV, or ARA
can be placed in AN/ARC-5 receiver racks without damage to anything.
The AN/ARC-5 manuals even say so.  But...not transmitter components!

And, as far as the USN's original ARA/ATA vs. the USAAF's SCR-274-N goes,
all components of one system will interchange with the other.  The only
electrical difference is the 600 ohm audio impedances of receiver output
and the modulator sidetone in the ARA/ATA, compared to the 8000 ohm audio
impedances found in the early SCR-274-N (later changed to support either
600 or 8000 ohms).

BTW, it is much harder to complete an AN/ARC-5 system than it is to 
complete an SCR-274-N system.  The racks and connectors and control boxes
for the AN/ARC-5 are much harder to find and usually much more expensive
(especially the connectors).  The major components of the SCR-274-N are
the easiest and cheapest to obtain as well.

I have put together a complete SCR-274-N plus AN/ARR-1 set (3-receiver,
2-transmitter racks), and a complete AN/ARC-5 plus AN/ARR-2 set (3-receiver,
2-transmitter racks).  I'm now working on the ARA/ATA plus ZB-3.  Putting
together complete sets is an entertaining and satisfying endeavor.  But
it can take many years and some cash outlay to do it properly.  I would
recommend starting with the SCR-274-N.

BTW, it's reasonably certain you will never come across a 3-transmitter
rack in either the SCR-274-N or AN/ARC-5.  Very few ever existed.

Ebay will be your best supply resource.  Good luck!

Mike / KK5F