19-02-2017, 08:47 PM
I made my 25kV probe way back in the mid 1970s when I first acquired an ex rental colour TV and needed to be able to check the EHT. I had easy access to VR37 resistors (I won't say whose stores they came from but as in many cases the company concerned weren't too worried about engineers "borrowing" a few bits for personal use).
At 25kV and low energy there were no great problems in construction. The soldering was nice and neat, the whole string was in a PVC tube which in turn was in a paxolin tube. I connected a bleed resistor from the LV end of the chain to an earth clip and I think I had a guard ring part way up the probe which was about 10" long.
I wouldn't have liked to connect it to a high energy source nor to anything much over 25kV. There were 15 resistors in series, each rated at 2500V so in theory it was good to 37.5kV.
I use the probe to this day for TV EHT meaurements, including mains dervied EHT. I rebuilt it a few years ago to use a screw-in probe tip to replace the original tip which had broken in an awkward place.
At 25kV and low energy there were no great problems in construction. The soldering was nice and neat, the whole string was in a PVC tube which in turn was in a paxolin tube. I connected a bleed resistor from the LV end of the chain to an earth clip and I think I had a guard ring part way up the probe which was about 10" long.
I wouldn't have liked to connect it to a high energy source nor to anything much over 25kV. There were 15 resistors in series, each rated at 2500V so in theory it was good to 37.5kV.
I use the probe to this day for TV EHT meaurements, including mains dervied EHT. I rebuilt it a few years ago to use a screw-in probe tip to replace the original tip which had broken in an awkward place.
www.borinsky.co.uk Jeffrey Borinsky www.becg.tv
