AM Radio discussion. Directional arrays are FUN!
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I am trying to figure out what divider ICs were used in the MF version of the Collins 310W-1 exciter (used in the 820E-1 and 820F-1 transmitters). The part number is crossed out in the manual copy that I have access to, which is actually for the HF version which does not use the divider ICs. The part looks like SC2239 but is hard to make out because of the heavy line through the part number. From the print they appear to be individual type D flip-flops in 8-lead TO-5 cans. In the exciter in my care they were replaced with a circuit built around a 7474 dual-D flip-flop - the whole circuit, including wire and perf board, was made from parts bought at Radio Shack, perhaps in the late '70s. Using the Q and Not-Q outputs of the second flip-flop to directly feed the bases of the driver transistors in the exciter was a poor choice. The load is not one that conventional TTL is happy with, the exciter output level could never have been as high as the original design (although it worked passably for many years) and it eventually damaged the 7474. I replaced the chip and added .01 uf capacitors to DC-isolate the 7474 outputs from the driver transistors and reduce loading on those outputs. The exciter now exceeds the factory spec for nominal output power and the 820E-1 is very happy.
Dale H. Cook, Contract Engineer, Roanoke/Lynchburg, VA
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