RK05 spindle pulleys - trade 50Hz vs 60Hz?

Tony Duell ard.p850ug1 at gmail.com
Wed Jul 25 22:32:49 CDT 2018

> There are, however, DEC products other than the RK05 which had different
> transformers for 50 Hz and 60 Hz. For example, the H771 power supply used
> in the RX01 and RX02. There were three H771 models, The H771A for 90-132
> VAC 60 Hz, The H771C for 90-132 VAC 50 Hz, and the H771D for 180-264 VAC 50
> Hz. The H771A uses a transformer rated for 60 Hz. The H771C and H771D both
> use the same 50 Hz rated transformer, with different wiring. The H771C and
> H771D also require one of two different wiring harnesses to cover the
> entire mains voltage range, e.g., 90-120 VAC vs 100-132 VAC for the H771C,
> or twice those voltages for the H771D.

IIRC that's a ferroresonant transformer (with a capacitor to resonate one of the
windings to a harmonic of the power line frequency), so it's not
surprising it has
to be changed for 50Hz or 60Hz input.


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