Re: Apple 5.25 Diskettes?

[david@uow.edu.au (David Wilson)]

Patrick Schaefer <pa.schaefer@fz-juelich.de> writes:
>Paul Guertin wrote:
>> Would it be possible to replace the drive head in a Disk ][
>> with a high-density head (that presumably has a stronger, more
>> concentrated magnetic field) and expect it to work without too
>> many modifications?

>You would have to replace the head amplifier, too. The easiest way
>should be using a complete TEAC55GFR HD drive with an Erphi or Ehring
>controller (PC drives need Step and Direction pulses instead of the four
>phases, therefore a Disk II controller cannot be used).

I have a TEAC drive on my MPF-III (a //e clone by Multitech) which has a
small card that converts the Disk ][ interface to the standard 34 pin FDD
interface (converting the 4 phases to step and direction signals). This is
my favorite 5.25" drive in my Apple // collection - the card uses the track
0 sensor to disable outwards stepping so no more head banging at boot up.

I must build another one of these with the drive select converting to head
select and use my 80 track drive in DD mode to give 640KB disks on a Disk ][
controller. Alternatively I could arrange all the even tracks on one head and
the odd ones on the other, then I could run two drives off one controller -
they would look like 160 track drives.

>There may still be a problem: HD drives expect a 500 kHz data stream
>instead of 300 (250) kHz.

Agreed. They also spin at 360 rpm instead of 300. Thus you would actually
get less data on a track with GCR than you would on a standard 300rpm drive.
--
David Wilson  School of IT & CS, Uni of Wollongong, Australia