[R-390] Rube Goldberg 400 cycle ac

[Peter Cade]

Just a thought, if you're looking for small amounts of 400Hz power.

I once bought a vacuum state gyroscopic fluxgate compass, just 'cos it
was a cheap, and  nice looking piece of WWII machinery. It needed  28V
400Hz, 50 watts or so, and after puzzling a bit, I pulled out an old
audio power amplifier (more robust vacuum state stuff - a Dyna mkIII I
think), hooked it up to a audio sine wave oscillator, set the thing for
400 Hz, connected the thing up and adjusted the output to give me more
or less the right voltage. 
Voila... the gyro spun up, the tubes lit, and I was able to point myself
north !