50 Hz Shugart SA-851s...

[Dwight K. Elvey]

Hi Bill
 When I was helping a friend bring up a MDS800 system,
years ago, the only cheap drives we could find were
the ones for the 50Hz ( surplus ).
 We just took a file to the motor spindle and ground
it down until is was the right speed. Do note that you
need to keep a little crown on the pulley to keep
the belt centered.
 I do think that the belts are slightly different.
As I recall we also had to elongate the mounting holes
for the motor to keep the belt tight. It may be that the
flywheel pulley is slightly different to use the same
belt size but I'd think a different belt makes more sense.
We didn't have a 60Hz drive to compare to at the time.
Dwight

>From: "Bill Sudbrink" <wh.sudbrink at verizon.net>
>
>In the process of getting Dave Dunfield a door button for
>his Seimens 8 incher, I went through my whole stack of 8
>inch drives and parts.  I "found" a couple of SA-851s that,
>while the serial number plate says they are 115 volt, 60 Hz,
>are in fact built with the 50Hz drive pulley.  You can put
>them next to a "normal" SA-851 and see that the pulley is a
>different size and I just confirmed it by putting a diskette
>in one, powering it up, putting a scope on the index signal
>and seeing that (on 60 Hz power) it is turning at 432 RPM a
>20 percent increase over the 360 rpm it should be turning at.
>Other than that little problem, the drives seem to mostly
>function, that is, they seek, report track zero, etc.  They
>appear to have seen very little use (probably because they
>don't fully work).  Anyway, they weigh a ton (like most 8
>inch drives) but is there anyone within reasonable shipping
>charges of Washington, DC that could use them and would want
>to work out a trade?  Alternatively, it just occurred to me
>that maybe I could just exchange pulley wheels with someone?
>
>Bill S.
>
>