[Milsurplus] TCS: T-17 and RS-38 Microphone Mystery

[AKLDGUY .]

Both the TCS and the BC-456 modulator (SCR-274N) use the Ring of the
Tip-Ring-Sleeve jack, so that's not the problem.
Are the heaters in the BC-456 being supplied with 24-28 VDC, or is it AC?

73 de Neil ZL1ANM