Chuck Guzis cclist at
Thu Feb 4 01:17:22 CST 2021

On 2/3/21 5:59 PM, Fred Cisin via cctalk wrote:

> He humbly acknowledged things that he didn't know, actively solicited
> comments and suggestions, and compiled a really nice collection of some
> of the weird formats.  (including a link to Chuck's F85 page)

I didn't ever send him an F85 diskette, just a sampling file from a
Catweasel.   One thing about those 5.25" 100 tpi diskettes is that data
is clocked at about 350 KHz, as opposed to 250 KHz for a standard drive.

The upshot is that even you find a 100 tpi drive, the drive electronics
probably will require a bit of "tweaking" to give a bit more headroom in
the bandpass.  When I tried a stock MPI 52 100 tpi model, I had to
modify it slightly to get it to work reliably; same for a Tandon
TM-100-4M.  I think Micropolis drives worked without modification, but
the ones I have are single-sided and so haven't been used in some time.

One of the things that I meant to get around to doing, but never did,
was to take one of my Drivetech 5.25" drives and add my own PCB to do
the micropositioning.  (Those drives have two positioning steppers on a
sort of lever arrangement--one for coarse and the other for fine).
Nominally, the drives are 192 tpi and use an embedded servo for the
high-capacity capability (which is why the drive couldn't format its own
high-capacity floppies).


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