[Milsurplus] need info 440hz xfrmrs and OS-10/U

[Patrick Jankowiak]

I have built a few inverters/converters for 400Hz. One thing I 
have learned is that the turns per volt on higher frequency 
transformers can be much lower. With 400Hz, you can also operate 
with higher voltages on a 60Hz transformer if the insulation will 
deal with it. (just the opposite of when folks use 24VAC 60Hz on 
a 110VAC 400Hz selsyn motor for classroom demonstrations, anyone 
recall that?)

I needed 115V 400Hz sinewave at 180 watts for a 618S-1 project. I 
had tried a 12VCT to 120V transformer, but I did not have enough 
headroom to make the peak voltage without distortion on the 
sinewave at full load. It would have been fine for square waves, 
but I wanted a sine wave.

Therefore I used a 6.3VCT 20A transformer with primary driven by 
a bank of push-pull 2N3055's running on 12VDC. The 115V RMS 
output regulation was obtained by dividing the output voltage, 
rectifying it, and feeding it back to the driver stage's emitter.

It's not very efficient, maybe 50%, but it drove the servomotors 
in a Collins 618S-1 very nicely. Sine waves are best for servos 
both from an electromechanical point but also from a physical 
noise point. The 400Hz power required for the 618S-1 is about 180 
watts (counting the 320-1000Hz requirement, which I ran at 400Hz).

If you want to use that transformer on 'house current', you can 
use a full wave voltage doubler and then from the 320VDC output 
of that, power an amplifier which will produce a 320V peak to 
peak (113VAC)sinewave at 400Hz. Or, use an old audio amp and step 
up the voltage with an external transformer.

Sorry to drone on, but I've had alot of fun with 400hz stuff.

Patrick