High voltage DC power supply

Most hobbyist electronic labs are equipped with a variable voltage power supply of some kind. It could be a benchtop commercial box, a modified AT PC PSU, a variable step-down circuit on the output of a 20-30V upcycled (laptop) power supply.

At some point I realised I was missing an important power source for my never ending learning experiments: a variable high-voltage DC power supply. I mean something that would output as much as 300Vdc regulated (I've build it with a switcher, with back-to-back transformers and voltage multiplier) and high current, possibly limited (neither easy nor cheap).

Not long ago in the neonixie mailing list someone mentioned buying a second-hand electrophoresis power supply. A quick check on eBay showed it would cost me 60-100€ for a device capable of 300V and few hundred mA. Unfortunately all of them are in USA or in UK, with large shipping cost. I think there is very little Italian second-hand market for these devices because professional labs need lots of certifications etc etc and probably rent/lease them.

So I patiently waited for something in Italy to be sold online and before the COVID-19 lockdown I bought a second-hand Bio Rad Power-Pac 300: a whopping maximum of 300Vdc at 400mA, digitally controlled.

The power supply at 300 V output between older devices. The Philips DM needs calibration...

The voltage regulation goes from 10 to 300V, while the current can be limited between 5 and 400 mA. Or vice-versa. The only drawback is a minimum load of 4 mA regardless the output voltage, that I can overcome inserting a fixed resistor in one of the 4 parallel outputs.

With 400 mA available I can power a lot of Nixie tubes and valve-based equipment. Or experiment the beauties of electrophoresis!