0 - 5 kV Hi-Pot Tester

Hi-pot testers are very useful tools for testing breakdown voltages of various components. After years of 'getting by' without one, I had a specific need for one - testing 4CX1000A / 4CX1500B tubes for gas ... before plugging them into a 2-meter strip-line amplifier and potentially having it go boom! Of course there are numerous other uses for a hi-pot tester ... such as testing transformers, chokes, variable capacitors, vacuum relays etc.

An article published on the Grey Hair Net website convinced me it was time, actually past time, to build one of my own. That original information and schematic diagram can be found at www.greyhairnet.org/hi_po_tester.htm. The pictures shown here is my concept of how to build a conveniently packaged unit using suitable components that, for the most part, were purchased on ebay for a relatively small cash outlay.

The Pelican 1300 case that houses the hi-pot tester was an ebay find - used but in good condition at $12.50. It makes for convenient and safe storage when not in use. The ac cord and test leads can be stowed under the cover.

The powerstat is the smallest one I could find - an Ohmite Ohmitran model VT1N purchased off ebay for $3.00. A 3500 volt transformer was also sourced from ebay and was the most expensive item in the project at $20.00. An unwanted bug zapper would have been a good source for that part but none were readily available. A 12 kV microwave oven rectifier, CL01-12, also came from ebay. These were 3 for $5.00. The .01uF/6 kV capacitor came from Mouser ($3.50) and the 25 Megohm / 15 kV current limiting resistor is an IRC MVX-3 ... purchased on ebay for $9.00. Ebay also turned up a nice Modutec 50 uA meter at $3.50.

The remainder of the parts used in the project were junk box items. One could cut costs by using virtually all junkbox parts. A series string of lower voltage rectifiers in place of the single HV rectifier would certainly suffice as would a string of lower voltage resistors in place of the HV resistor and a string of lower voltage capacitors in place of the HV capacitor. In my case I preferred a quick and clean assembly rather than using perf boards to hold the series strings of parts. I used Millen high voltage connectors since they were available. Ordinary banana jacks would have worked equally well. All parts are mounted to an 1/8" thick piece of phenolic cut to fit the Pelican case. A dial/voltage calibration sheet was made and attached to the inside of the case cover.

The hi-pot tester was invaluable in testing the external anode transmitting tubes - the original reason for building it. It was also used to 'debarnacle' (as Eimac calls it) an NOS 1968 vintage 4CX1000A after repeated 'gettering' failed to reduce plate-to-screen leakage current. It has also been used to test a number of vacuum variable capacitors, vacuum relays, transformers and other components. After getting by for many years without a hi-pot tester, it's nice to have one readily available!