[Milsurplus] BC950 Army 274N VHF tx

[David Stinson]

From: milsurplus-bounces at mailman.qth.net
[mailto:milsurplus-bounces at mailman.qth.net] On Behalf Of Larry Smith
Subject: [Milsurplus] BC950 Army VHF tx

 

I am seeking info on this tx which is similar to the arc5 T23.   Some of the
t23's have a unused tube socket cutout that accommodates a 815 tube in the
bc 950.   I think this tube is for modulation, but not sure.  I have the
army 274N manual and the arc5 vhf manuals and no info on the 950.

Larry KB6OO

 

The 815 in the BC-950 is indeed an internal plate modulator.

 

The BC-950 is the immediate U.S. Army ancestor of the AN/ARC-5 T-23.

It was designed to plug-into the SCR-274N Command Set system to provide

a VHF capability for that set.  To change a 274N from MF-HF to MF-HF-VHF

required  that one remove one HF transmitter and one HF receiver, 

install the BC-950 transmitter and BC-942 receiver, change the control

boxes, plus a bit of added cabling.  The connector on the back of the 

BC-950 is the smaller one for SCR-274N.  The 950 is not compatable with

the AN/ARC-5 system and is not interchangeable with the T-23.

 

Only an estimated 1000 of the Army Signal Corps versions of the 

274N were produced.  The Navy submitted improvements to Western

Electric to use the sets as a VHF addition to AN/ARC-5.

Most of the Army sets were re-worked into the AN/ARC-5

T-23 transmitter and R-28 receiver.  The plugged holes

In the front of chassis of the early T-23 were for the 815 modulator.

Since the 274N screen modulator was not workable with the 832

VHF PA, the W.E. engineers came-up with the great idea to capacitor-

couple the the modulation audio from the screen power supply 

into the 815's grid input transformer.  

 

The majority of BC-950s were re-worked into T-23s and they 

are scarce, but not rare.  No example of a BC-942 receiver with its

original Army nomenclature tag is known to have survived, but you 

can tell one that was originally "Army" by its Army inspection markings,

internal markings and diagrams that are clearly Army, "Army" marked 

tubes and occasionally, it will still have its I-101 frequency selector

which was later upgraded to the I-102.  

 

Very little documentation on the Army -274N VHF has survived;

in fact, I have just in the last couple of days discovered some and

will be posting about it soon.

 

A couple of years ago, I managed to assemble a complete

SCR-274N MF/HF/VHF set and have it working well.  Listen

to local aircraft on it and have made a couple of contacts.

 

More information on how we got it going is available if interested.

 

GL ES 73 OM DE Dave AB5S

 

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