National Multiplex data cassette tape drive

From: Ed Kelleher <>
Date: Wed Aug 25 15:30:57 2004

At 02:26 PM 8/25/2004, you wrote:
>On Tue, 2004-08-24 at 17:09, William Maddox wrote:
> > Years ago, I owned a data cassette drive made by a
> > company called National Multiplex, presumably long
> > defunct. ...
>Ugh! I had one on my SWTPC, around 1975? It was the first time I got
>ripped off buying computer gear.

About that same time I found a purpose built data cassette (Philips type)
drive from Braemar Computer Devices in Minnesota.
The CD-400. I had to build something to read ECMA format cassette tapes
from NCR data entry devices and convert them to 7 track 1/2" mag tape for a
Burroughs B300 data processing shop.

The tape drive was great.
TTL control of motion and decoded NRZ data plus clock I/O at 800BPI.
But they cost about $600 in 1976.

Used the Motorola M6800 Microcomputer Systems Design Evaluation Kit to
make a prototype system to read the cassettes and output to a Mohawk key to
7 track tape unit.
The tape drive only had 1 reel. The tape dumped into a hopper as the
operator key punched.
Then it rewound. Strange machine, made a great clacking sound when it
wrote the tape.

Eventually wrote a cross-assembler for the 6800 in Dibol for PDP11's
and made 5-6 of the machines for the companies branch offices.

Received on Wed Aug 25 2004 - 15:30:57 BST

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