Bought another old power supply - Oltronix D400

[JohanH]

I bought this old 400 V laboratory power supply. It worked, kind of, but I quickly found issues and began examining it. Finally wrote a blog post about it, with a comprehensive description of the circuit design and the components:

Blog post Oltronix D400

It's another 1960s-era design from Oltronix. It provides 0–400 V / 70 mA or 0–200 V / 140 mA DC output and has also two 6.3 V 2.2 A AC outputs.

I'm planning on recreating the regulator/error amplifier board (the section within the dashed line in the schematics), because it's in a such a bad shape and it's hard to fit modern replacement components.

[JohanH]

I created a second blog post about this power supply after creating a new regulator PCB, which I also made available on Github.

https://baldpenguin.blogspot.com/2026/06/repairing-oltronix-d400-007d-part-2.html

In the article, I also include practical component substitutions and ordering examples.