9 Jun
2020
9 Jun
'20
11:54 a.m.
Den tis 9 juni 2020 kl 19:04 skrev Ethan Dicks via cctalk <
cctalk at classiccmp.org>:
On Tue, Jun 9, 2020 at 10:46 AM Jon Elson via cctalk
<cctalk at classiccmp.org> wrote:
DEC's transistorized machines used +10V and -15V supply rails for the
logic, and some other large voltage (+28V?) for the core.
Later machines still used odd voltages. Lamp-based PDP-8 front panels
used voltages like +8V, and later core was IIRC +20V.
There are a couple versions of the PDP-8/a PSU, for core memory and
for MOS memory. MOS memory is standard 1970s triple-voltage stuff
(4096s and 4116s) but they pull a lot of +12V compared to later
machines.
It's often easier to just fix the old PSUs than replace them. At
least linear supplies aren't so hard to debug.
The MOS PDP-8/a PSU provide +5V, +15 and -15V. So no 12 V there.
The Core PDP-8/a has -5V and +20V for the core memory.
To be able to test and debug Omnibus boards in my lab (aka garage) I
converted a MOS 8/a box into switched PSUs. Managed to squeeze five single
output PSus in the box to be able to run both 8/e core memory (which
require quite a lot -15V) and also newer 8/a core memory in it.
It is so much less heavy to move around on the lab bench.
https://i.imgur.com/3DW9ukm.jpg
/Mattis
On 06/09/2020 09:27 AM, Anders Nelson via cctalk
wrote:
> Related question: Is there any reason, other than historical accuracy
and
> cost, to not replace the power supplies in
vintage computers with
modern
switching
power supplies?
The old discrete transistor machines often used fairly odd
voltages, not like 5V and 12V. 
-ethan