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. -ethan
