Radio Transmitters BC-191-A, BC-191-B, BC-191-C, BC-191-D, BC-191-E, And BC-AA-191 - TM 11-800 War Department Technical Manual

1. Differences in models. — a. Radio transmitters BC-191-( ) and BC-AA-191 with their associated equipment are designed for use as component parts of radio sets installed in aircraft, armored cars and other vehicles, as well as in portable ground stations. The basic circuit arrangements of the two types are similar. However, the older type BC-AA-191 requires the use of certain external equipment. In the BC-191-( ) transmitters the equivalent equipment is built into the transmitter case. In addition, the BC-191-( ) transmitters have greater frequency stability under varying temperatures and incorporate numerous circuit and mechanical refinements. b. In general, the various BC-191-( ) types are alike. The BC-191-A, the first type issued, and the BC-191-B, are alike except for improvements in the latter in the rotary antenna loading coil 1170 and the switching relay 1165. The BC-191-C, the third type issued, has a toggle type OFF ON switch 1194 in place of the rotary type 1132 on the older sets. In addition, the A-C D-C and 12V. 14.2V. switches 1195 and 1190 respectively are of different design from the old switches 1136-1137 and 1139-1140 which they replace. A number of other minor changes distinguish the BC-191-C from older models. The faces of the panel meters are black with white lettering, while on the older models the faces are white with black lettering. c. Radio transmitter BC-191-D is like BC-191-C except for a redesigned filament resistor connection board and a redesigned antenna leading switch 1198 replacing switch 1171. These parts are interchangeable electrically and mechanically with those in the BC191-C. Radio transmitter BC-191-E includes the changes of the BC-191-D and in addition has a single unit filter capacitor block 1197a, 1197b, and 1197c, replacing three individual capacitors 1120, 1155, and 1163 in the older models. This part is interchangeable electrically, but not mechanically, with the three units it replaces. ♦For simplicity, radio transmitters BC-191-A, BC-191-B, BC-191-C, BC-191-D and BC-191-E will be referred to as BC-191-( ) in this manual when remarks are applicable to all such sets. The ( ) indicates all five types. Radio transmitter BC-AA-191 is always referred to as BC-AA-191. ♦♦Numbers refer to parts indicated by same numbers in illustrations and diagrams in this manual. S d. Radio transmitter BC-AA-191 makes use of transmitter tuning units with the designation TU-AA-( ). There are eight of the units marked from TU-AA-3 to TU-AA-10 in consecutive order. Radio transmitters BC-191-A, BC-191-B, and some BC-191-C types use transmitter tuning units of the TU-( )-A type. There are nine such units available for full frequency coverage. A typical unit is TU-5-A. Later models of the BC-191-C and all BC-19i-D and BC-191-E transmitters are supplied with transmitter tuning units of the TU-( )-B type. For example, TU-5-B. The only difference between the A and B types is that the B type does not have the two insulated binding posts found in the upper right-hand corner of the front panel of the A type. These posts are not required for operation of the equipment but are a convenience in some servicing operations. They are connected to the tapped secondary of the power amplifier tank circuit through control ANT. COUPLING SWITCH D. e. Due to the differences in location of controls, appearance, adjustments, and operating procedure between radio transmitters BC191-( ) and BC-AA-191, this manual has been divided into two parts, the first dealing with the newer BC-191-( ) types, and the second with the older BC-AA-191. f.

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