RK05 spindle pulleys - trade 50Hz vs 60Hz?

Guy Sotomayor Jr ggs at shiresoft.com
Wed Jul 25 13:27:33 CDT 2018

> On Jul 25, 2018, at 11:17 AM, Tony Duell via cctalk <cctalk at classiccmp.org> wrote:
> On Wed, Jul 25, 2018 at 5:48 PM, Eric Smith via cctalk
> <cctalk at classiccmp.org> wrote:
>> I'm not sure about motors, but 60 Hz power transformers can't handle as
>> high a maximum power (or current) when used for 50 Hz. The maximum power
>> has to be derated. Some transformers are specified/sold with a single power
>> specification for both 50 and 60 Hz use, which just means that the vendor
>> has built the necessary derating into even the 60 Hz specification.
>> 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.
> Does anyone have an RK05 IPB (Illustrated Parts Breakdown) manual? It would
> be interesting to see if there are different part numbers for the motor (start
> capacitor, blower...) for 50Hz and 60Hz versions.
> Going back to a much earlier comment, I think this pulley is something that
> would be a lot easier to turn (on a lathe) rather than 3D print.

A while ago (can’t recall how many years), I acquired a number of 50Hz RK05’s.
Since I live in a 60Hz country, getting the drives to work simply involved changing
the pulley from the 50Hz version to the 60Hz version and changing the voltage
jumpers (the drives have worked fine after that change).  I believe that the switch
over is documented somewhere…but it’s been *way* too long since I did it.

As far as I recall, the pulleys have the frequency stamped on them.

For the OP who started this thread.  Yes, I still have the 50Hz pulleys *somewhere*
but at this point they're not easy to find as they are packed in a tote in the basement
of my shop (which is packed floor to ceiling with boxes and totes…there isn’t even
an isle to walk around in…just a small area that you can almost turn around in).

TTFN - Guy

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