Monthly Archives: July 2015

Satisfying my curiousity about the original Cockroft-Walton voltage multiplier

I was reminded of the Cockroft-Walton voltage multiplier recently, because I was thinking about building a small one for fun, and upon seeing that their development of this started in 1932, I was curious about some of the details of how they built it. In particular:

  • Were there any sort of usable high voltage solid-state rectifiers then?
  • If not, what kind of tube rectifiers were they using?
  • If hot cathodes as I would expect, how did they provide the heater supply isolated at voltages in excess of 100 kV
  • What was the output of their original multiplier?

Turns out their 1932 articles are easy to find and fairly pleasant reading:

The first article is mostly about the high voltage generator, and the second is mostly about what they did with it. In essence they produced about +700 KV and beam currents (positive hydrogen ions) on the order of 10 microamps. Most of the current was lost to corona discharge, they state that it was over half a milliampere. The interesting thing is that they did use a custom-built version of the standard hot cathode vacuum diode. The filaments were each heated by “6-volt accumulators”, which in my understanding probably means a lead acid battery. There are a lot more details about the vacuum system, naturally it takes quite a while to completely pump down the apparatus to operational levels.

Anyway, if you are interested in high voltage gadgetry or experimental physics, you should read the linked papers, they’re quite enjoyable. (Edit: Actually, there are 6 papers in that series, see this search result.)