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

17 Aug 1999

Well . . . freight cost alone might be justification for using switchers.
Nevertheless, I don't see a use for the regulated supplies in connection
with a bus which by definition uses on-board regulation.  If the supply
actually provides the specified voltages, that's a different situation.  The
typical S-100 box, IIRC, used lots of amperes, even for just one memory
board, and generated lots of heat.  The average, even BIG, PC supply is not
beefy enough to support a typical S-100 box as I remember them.  8 of the 8K
SRAM boards with 2102's . . . well, you figure it out!  There were other
ways to go, of course, but back in the day of the 22-slot backplane, that's
what justified the backplane's size.  Power for the entire remainder of the
system was not that much.

Dick
-----Original Message-----
From: Jeffrey l Kaneko &lt;jeff.kaneko(a)juno.com&gt;
To: Discussion re-collecting of classic computers
&lt;classiccmp(a)u.washington.edu&gt;
Date: Tuesday, August 17, 1999 4:33 PM
Subject: Re: imsai 2

...

On Tue, 17 Aug 1999 16:11:10 -0600 "Richard Erlacher" &lt;edick(a)idcomm.com&gt;
writes:

<Stuff SNIPped>

  What puzzles me is why the IMSAI folks decided to
use a switching
 power supply when the box and everything else already supported the needs
  of the S-100 with the previously available and
now quite inexpensive
 unregulated supplies of yesteryear. 
Well, for a given wattage, switchers are smaller, lighter, and more
economical to produce.  I imagine if they resorted to the old iron-core
transformers of yore, they would have had a difficult time finding
a supplier for them.

When they did, the part would probly cost as much as the rest of the
materials put together.  Makes perfect sense to me.

Jeff

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