RK05 spindle pulleys - trade 50Hz vs 60Hz?

Eric Smith spacewar at gmail.com
Wed Jul 25 14:45:47 CDT 2018

On Wed, Jul 25, 2018 at 12:17 PM, Tony Duell <ard.p850ug1 at gmail.com> wrote:

> On Wed, Jul 25, 2018 at 5:48 PM, Eric Smith via cctalk
> > Some products were built using different transformers for 50 vs 60 Hz
> > models, and the 60 Hz models uses a transformer inadequate for 50 Hz
> > operation.
> This may well be true (I think it is), but the original question was about
> a
> particular device, the DEC RK05 disk drive. According to the maintenance
> manual (on bitsavers), the coversion between 50Hz and 60Hz involves
> changing
> the motor pulley. No comment about replacing the motor, the start
> capacitor,
> or anything else.

Right. I was just responding to a later, general comment about motors.
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.

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