National Multiplex data cassette tape drive

From: Bill Dawson <whdawson_at_localisps.net>
Date: Tue Aug 24 23:23:30 2004

> Years ago, I owned a data cassette drive made by a
> company called National Multiplex, presumably long
> defunct. It was obviously a modified audio cassette
> recorder, but in which the internal electronics had
> been completely replaced. Unlike the prevailing
> standard for cassette-based data storage on micros
> in that day, this drive used saturation recording
> (NRZI, I believe) instead of a modulated audio carrier.
> It was a very functional replacement for a paper tape
> reader/punch, and ran up to 9600 bps using hi-fi grade
> audio tapes.
>
> I would be interested in locating one of these beasts
> to replicate the setup I had on my IMSAI before I sold
> the drive years ago. The drive came with schematics,
> and as far as I remember, the circuitry was rather
> simple -- a couple of op amps and a few gates.
> Alternately, if I can locate a copy of the drawings,
> I may attempt to reproduce the design using a
> contemporary audio cassette mechanism.
>
> Has anyone ever seen one of these?
>
> --Bill
>

Yes, I still have the one I used with my SWTPC 6800,
along with the supplied documentation. The unit is
just a modified portable cassette player. National
Multiplex gutted the usual cassette player-recorder
circuitry and installed their circuit board. They also
increased the tape drive speed (by changing the diameter
of the drive motor pulley, IIRC). There were several
models, but they were all called Computer Aid. The square
black plastic model CCA-7 was the most popular and are
the ones I have. This model has the level meter on it.
I found and purchased another on eBay several years
ago, so they're still out there. Another model is the
rectangular silver Computer Aid model DC-3. If I come
across my documentation for it (I have a good idea where
it is, I just don't have the time to look for it), I'll
scan it and send you the url. It'll be on swtpc.com
somewhere.

Bill
Received on Tue Aug 24 2004 - 23:23:30 BST