imsai 2 - test-drb@ccmp.vtda.org

17 Aug 1999

I suspect that there's quite a little work to be done on the IMSAI product
before the first fully functional one will be shipped.  I've got standard
switchers which would do the job, i.e. their outputs can be adjusted to
provide the needed current, e.g. 8V at 25 Amps, +/-12 16 @ 5 & 3 amps, or
maybe less.  These weigh less than the transformer supplies on the half
dozen or so S-100 frames I've got, and, when size and weight are viewed from
the standpoint of handling, storage, and shipping costs, they may even cost
less.  However, unless one anticipates volumes in excess of 1% of annual PC
sales, the cost will not be comparable with PC supplies.

Dick
-----Original Message-----
From: Eric Smith &lt;eric(a)brouhaha.com&gt;
To: Discussion re-collecting of classic computers
&lt;classiccmp(a)u.washington.edu&gt;
Date: Tuesday, August 17, 1999 4:45 PM
Subject: Re: imsai 2

...
 Tim wrote:
  According to what I read from the web page,
there's a PC-clone switching
 power supply followed by a "boost" switching circuit to get back to
 +8 and +/- 16.  That's not completely unreasonable, but it sounds a
 little bit fishy to me in the sketchiness of the details. 
It sounds a *lot* fishy.  For the required current, it would be more
expensive to try to use a standard PC supply with custom step-up converters
on the outputs than to simply:

1)  Hack a stanard switcher

2)  Build a custom switcher

3)  Have one of the switcher manufacturers build a slightly customized model
...

I've been thinking about replacing the power supply in my IMSAI because
the transformer has shorted turns and is delaminating.  I've been looking
at stuff from Vicor.  Not cheap, but high quality and reliable.