Den tis 9 juni 2020 kl 19:04 skrev Ethan Dicks via cctalk < cctalk@classiccmp.org>:
> On Tue, Jun 9, 2020 at 10:46 AM Jon Elson via cctalk > <cctalk@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. > 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 > > -ethan >