Below you will find application data for the two "five meter" test sets that may be useful. They are divided into the four major food groups of the command set series: RAT, ARA/ATA, SCR-274N, and AN/ARC-5. The individual 3.5" meter movements themselves are the familiar Weston Model 301 series, with internal shunts or series resistors to customize their range for the function desired. For the voltmeters, the load placed on the DUT is printed on the meter face: 62 ohms per volt for the 30 volt full scale Input Voltage meter; 1,000 ohms per volt for all of the Screen and Plate Voltage meters.
The first diagram below is from the original 1939 manual for the Navy Model RAT pair of receivers.
The second diagram is from the Navy Model ARA and ATA manual.
The third set of diagrams, these for the SCR-274N, starts with one from an original Signal Corps SCR-274-N "Handbook of Instructions" produced by the Aircraft Radio Corporation under Contract Order No. 1470-NY-1941, with an initial order quantity of 4,000 in November 1941, and an additional quantity of 25,000 in May of 1942. This contract and quantity information is only contained on the cover and first page. Strangely enough, despite it being marked "Published by Authority of the Chief Signal Officer", I can find no T.O. or other Signal Corps number anywhere else in the manual. It has an odd note that appears nowhere else, concerning the cable used between the test set and the transmitter under test (CD-530) that indicates a modified PL-154 on one end and a special plug (ARC #7843) on the other end.
By the way, this is the only document I have found that reflects any application detail on the I-71-B remote RF ammeter being used in the command sets, and sporadic brief mentions of it occur elsewhere throughout the manual. It seems to have disappeared in later versions.
The final diagram is from the last of the series, from the AN/ARC-5 manual. Note that the connectors in the 9556 transmitter test set have been updated to the same new 12 pin connector used in the AN/ARC-5 modulators and transmitter racks, etc., which are different from those of all earlier sets. Despite the warning on this last drawing, all earlier transmitter test sets can still be used by making up two special cables to use only with an ARC-5 set. This special cable would have an ARC-5 9377 connector on the end plugging into the ARC-5 modulator, and a PL-154 (ARC# 6964) on the end plugging into the older test set. Likewise with the cable between the test set and the ARC-5 transmitter under test. Appropriate wiring changes have to occur in the actual cable wiring, of course, but they can be derived from comparing the connections in the schematic drawings on this page. Fortunately, the 7369 receiver test sets can be used on all command set series without a problem.
