[Milsurplus] Re: BC-342/312, etc...

[W7QHO@aol.com]

Ken, All,

Been following this thread the last few days.   Did an article on these for 
ER a while ago (ER #95, March 1997).   Highlights from that tome follow:

There were 13 different BC-312 models: (no suffix), A, C, C, E, F, G, J, L, 
M, N, HX & NX.
For the BC-342: (no suffix), A, C, D, F, J, L, M & N

The antenna noise suppression circuit was included in the BC-312/342 (no 
suffix), A, B & early C.   At some point spares became unavailable and maintenance 
instructions were to eliminate this feature if any service required.   
Anybody have any operational experience with this scheme?

BC-312/342s through the A model had heaters in the HF oscillator compartment. 
  Some number of following models had fiberboard insulation only in the Osc. 
compartment. Later models had nothing.   I have no information on the 
changeover dates/models.

In the BC-312 and 342 (no suffix) and BC-342A models the shelf holding the 
6K7 RF and 6L7 mixer tubes is mounted parallel to the main   chassis.   On all 
subsequent models this shelf is slanted toward the main tuning cap.

All C and later models of both receivers had a second antenna terminal, a 
slip clutch on the "Fast Tune" knob and a backlash adjustment mechanism 
accessible from the front panel.

The chassis in "L" and later models is made of steel instead of the aluminum 
used in earlier models.   Also, the xtal filter was dropped in all   "L" and 
later BC-312s (except for the 28 volt "HX" see below).

There were two 28 vdc versions of the BC-312, the "HX" and "MX."   The 
BC-312HX had an xtal filter but the MX did not.   These sets also used a 12A6 in 
place of the original 6F6 second audio amplifier. 

Somewhere along the line aluminum cabinets were replaced by steel, perhaps at 
the same time that the steel chassis was introduced (see above).   Likewise, 
ceramic tube sockets were superseded by phenolic, stop pegs were added to the 
front panel to "GI Proof" the bandswitch, engraved labels were replaced by 
raised lettering, and the thin wire cursor in the frequency readout window was 
replaced by a line on a plastic insert.   The latter "improvement" does not age 
well, BTW.

The last Signal Corps equipment production that included these receivers was 
the MRC-2 which included modified BC-342s coupled together for diversity 
reception.   The best information I have is that the last BC-342/OA65s produced 
were manufactured by Dare Engineering in Troy, OH, for the AN/MRC-2D.

Hope this is useful.

Dennis D. W7QHO
Glendale, CA


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