[ARC5] crystal (BC-950-A)

[David Stinson]

The scarce SCR-274N VHF BC-950 transmitter does use the same crystals as the T-23, including the common CR1 types.  The BC-950 is not interchangeable with the AN/ARC-5 T-23.  As Mike mentioned, the modulator design is very different as is, of course, the rear connector.  

The BC-950 modulator is pretty slick.  Instead of swamping the excess amplitude of the BC-456 screen modulator (I'm not sure how well a 832 PA takes to screen modulation), the 950 samples the modulator audio impressed on the screen voltage and sends that to an 815 Plate Modulator stage.  Only a small number of BC-950s were completed.  Most were converted to T-23s, so they are scarce today.

If you have a T-23, pull the top and look between the front-most 1625 and the tuning motor.  If you see a hole with a hole plug, screw holes where the 815 went and washer-marks around the screw holes (and possibly an "815" marking), you have a BC-950 that was converted to a T-23.  If you find just the hole with the hole plug and no screw holes or screw holes with no washer marks, you have a T-23 which was already in the build-line when the changes to ARC-5 came out.  If you don't have the hole at all, you have a late-run T-23.

The 274N version of the receiver was also re-worked and became the ARC-5 R-28.  While one can find Army receivers that have been re-worked (can post the "tells" if anyone is interested), the original receivers with their Signal Corps nomenclature plates may be extinct- I've never seen or heard of one.

GL OM ES 73 DE Dave AB5S

P.S. Haven't posted this "Christmas Card" in awhile.
It's the SCR-274N set with 274N VHF.



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