BC-AA-191
The initial entry into the BC-191/BC-375 transmitter series appears to be derived from a commercial venture by GE in the 1932 time frame, called the RT-76-A. There are actually not that many changes to the set between this July 1935 BC-AA-191 and the ones used in the B-17 bombers through 1945. The most noticable is the absence of an integral antenna tuner and RF ammeter - the BC-AA-191 uses an external BC-AA-194 tuner that was connected through the two white ceramic binding posts at the top right of the tuning unit. Other than that and an external BC-AA-196 antenna relay, the circuit is essentially identical, using the same four 211 (VT-4) tubes and a Type 10 (VT-25) microphone amplifier in a classic MOPA circuit. It was an amazingly long lasting design...there are at least five different contract order numbers I have seen that run from 1934 to 1942 (with the majority prior to 1936.)


Entire system

The particular example below had something hit hard vertically on the right front of the top panel, requiring some delicate pressure to be exerted in an equal but opposite manner in order to straighten it.



The fixture shown below allowed careful pressure to be placed at the point of greatest bend without putting the brazed joints on the ends under undue shearing forces.



As you can see below, the result was entirely satifactory. Not done without a degree of apprehension, however...


Closeup of top after staightening


Closeup of frame after straightening


Receiver selector switch


Bottom view of wiring


Nomenclature tag on the transmitter


Typical nomenclature tag on a tuning unit.


Another nomenclature tag on a tuning unit. Note the date...this one may have been from an evaluation set.


This is the BC-AA-194 antenna tuner that will be going into the "flight deck" in the new "Prequel" position shown here.
It was later integrated into the BC-191-A and BC-375 series of transmitters to eliminate mounting a separate box.



Nomenclature tag from the above antenna tuner.


Here is an Espey manufactured BC-AA-194, (not GE), which has an inexplicable 1942 contract date, years after the 1934 BC-AA-191
was obsoleted by the BC-191-A and later models of the BC-191. Makes you wonder what the acquisition folks were thinking...
Notice the difference in meter design between the two.


Nomenclature tag from the above antenna tuner.

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