28 Nov
2010
28 Nov
'10
9:40 a.m.
On 28/11/10 02:40, Chuck Guzis wrote:
Qume drives used them. The other half of the puzzle
is the MC3471
write amplifier which seems to be a bit more uncommon. I've only
seen it on MPI/CDC drives.
Though the Motorola appnote Al linked to explains that you can do the
same thing with a constant-current source, DFF and a pair of switching
transistors. I suspect "fast" is the order of the day for the
transistors, which probably means the BC547 and BC847 aren't suitable.
Another popular circuit used on Tandon and Micropolis
drives as well
as quite a few other brands was the NE592 (identified as a video
amplifier, but perfect for floppy or tape read amplifier)
That's... tempting. The 592 is still a current part, which at least
makes repair a little easier. Though with five MC3470A chips in stock,
I'm not overly concerned about availability issues...
Although whether I've got enough clearance to shove a PDIP chip in there
without fouling the drive belt or flywheel is another question entirely...
--
Phil.
classiccmp at philpem.me.uk
http://www.philpem.me.uk/