Gregory's ServerA servo loop converts resistance to rotation. A motor rotates the gears while a feedback loop keeps it in the right spot. The amplifier generates an error signal to rotate the motor in the correct direction. The potentiometer indicates the current output.
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19 comments
 To correct for errors, a correction factor is added, a function of rotation. This is implemented with a metal plate, warped into the correct shape with 20 tiny screws. A cam measures its position, which is added to the rotation with a differential gear mechanism. Just converting a temperature to rotation took a big wedge of gears. Although gear-based computation is bulky, an analog computer was the best solution at the time.  @kenshirriff use a vfd! They go up to 400hz, and probably cost $100. I use a vfd for... reasons... you can adjust, well, everything. I got a 3 phase output but turned out I only needed 1 phase  @kenshirriff  @kenshirriff "glad" to see 115V/400Hz was already in use back in the 50s... @kenshirriff looking forward to reading/seeing more about it once you have a chance to power it up! i enjoy seeing this sort of thing that fits neatly at the intersection of #avgeek, #vintagecomputing, and a whole ton of other topics that escape me atm. @kenshirriff Why that particular voltage and frequency? Did the creators learn all their EE through dance instead of words? @Urethramancer Apparently 400 Hz is popular for avionics rather than 60 Hz because the higher frequency means the transformers are much smaller.
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 @kenshirriff That thing looks like a nightmare to keep calibrated once the parts start to wear...  @kenshirriff What errors does that encompass? I would expect that this accounts for nonlinearity of the sensor, and that there's no need to account for errors in the amplifier itself (because we don't rely on ~any other properties than behaviour at input equal to 0). Are there other sources of systematic error I'm missing?  @kenshirriff can you do a post on magnetic amplifiers some time? I've never quite got how they work and you do explain things very well and very thoroughly. |
They didn't have op-amp chips back then, of course, so the amplifier consists of multiple boards of circuitry. The boards have a few germanium transistors (pre-silicon) but transformer-like "magnetic amplifiers" perform most of the amplification.