17 Jun
2009
17 Jun
'09
2:46 p.m.
From: Dave McGuire
Sent: Wednesday, June 17, 2009 2:16 PM
On Jun 17, 2009, at 4:40 PM, Tony Duell wrote:
> But I don't lioke changing the classic
machine. Not even replacing PSUs
> with switchers. The original PSU is part of the design, and I want to
> keep it that way.
While I agree with you here, I have to admit that,
if my PDP-11/70
had switching power supplies, I'd probably run it a lot more often.
I'd *never* make it an irreversible modification, though.
Tony's comment was presumably brought on by Richard's passing mention of
the power supply work we have done to the 1090 and 2065 at PDPplanet. We
did this work in the spirit of those DEC customers such as CompuServe who
replaced the power supplies in their KL-10 systems beginning in the 1970s,
although we have been very careful to document every change and to make
them all completely reversible.
Here's why: The linear supplies used on the KL-10 are there because the
ECL circuitry is much more sensitive to noise in the power than TTL, and
the early switchers were extremely noisy. Modern switchers are very much
better on that count. Since the linears waste ~2/3 of their input power
as heat, replacing them means that instead of a 12.4KVA draw, we're down
to less 6KVA, which means it costs less than half what it otherwise would
to power these machines.
Rich Alderson
Vintage Computing Server Engineer
Vulcan, Inc.
505 5th Avenue S, Suite 900
Seattle, WA 98104
mailto:RichA at vulcan.com
(206) 342-2239
(206) 465-2916 cell
http://www.pdpplanet.org/