I have reason to believe that the CDC 9428 and 9429 are identical
except that the 9429 is jumpered for 80 tracks and the 9428 is
jumpered for 40 tracks... but I'm not 100% sure.
* On Sat, May 07, 2016 at 11:17:50PM -0600, Eric Smith <[email protected]> 
wrote:
They would have to have different heads, if the 40 track model was
standards-compliant and industry-compatible.

On Sun, 8 May 2016, Seth Morabito wrote:
Ahhh... of course, I should have thought of that.
I am even more cautious about using the 9428 manual for 9429
service, then.

Actually, many lines of drives, such as the Tandon TM100 have the same circuitry for both the 48tpi and 96tpi variants. (and the TM100-4M at 100tpi)

A specific exception, that I don't think is relevant here, is that a 1.2M drive will have a few circuitry changes V a 48tpi/"360K" model, such as RWC (reduced write current), and sometimes a 300RPM V 360RPM control.

But, a "360K" (CDC 9428) V "720K" (CDC 9429) are likely to be virtually identical other than step distance and head width.


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