[Milsurplus] 115 VAC 400 Hz tolerance, and the B-36

[Ray Fantini]

I have spent some time working with the servo systems in the Arc-38 family of radios and wasted lots of time getting fifties technology servo decks from APS/APQ radar working that use gyros and servo systems to compensate for aircraft altitude and in all AC chopper servo sub system know that frequency was important. Most of the systems are rated +/- 20 cycles or else it was outside the operational limits for the device. What would happen to a synchronous motor gyro if you double the frequency? Often you will find two AC inputs like on the ARC-38 with one input just feeding the power supply and fan and a second input just for the servo system that needs a higher tolerance of frequency control. I would speculate that's why DC to AC inverters was used because until constant speed drives were developed there was no way to control AC frequency or phase of multiple generators in a large aircraft until the post war forties or the fifties, goes back to the B-36 again. Trivia: the early versions of the B-36 used an ARC-8 (BC-348/ART-13) and later used AN/ARC-21 I am still looking for pictures, parts  or any information on the huge mysterious "drum" radio. Think the last time I brought this up the opinion was its extinct.
Ray Fantini KA3EKH