PDP-8/A transformer hum

[Anders Nelson]

Interesting, good to know!
--
Anders Nelson


On Tue, Jun 9, 2020 at 1:04 PM Ethan Dicks via cctalk <cctalk at classiccmp.org>
wrote:

> On Tue, Jun 9, 2020 at 10:46 AM Jon Elson via cctalk
> <cctalk at classiccmp.org> wrote:
> > 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.
>
> 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.
>
> -ethan
>