On Tue, Dec 14, 2021 at 09:42 AM, ken chalfant wrote:
Does anyone have an RPC HP-6 or BP-6 600Meg resistor, possibly rescued from a
Pomona 2900A high voltage probe, that you are willing to sell?
I'm guessing that this is what we used to call a "zebra stripe" HV resistor.
To find a replacement, we'd need diameter, length, and the threading in the end, and, of course, the resistance, 600 MOhms. The common specs are 3/8" diameter, length? and #6-32 threads. These tend to be hard to produce in tight tolerances, so when close tolerance is needed they are usually made by screwing together two selected resistors with half the length and ~half the resistance, one plus, one minus. When finished, the pair would be wrapped in transparent heat shrink and marked with the total resistance.
The transparent heat shrink also protects the carbon stripe that is the resistance element, as that stripe is quite fragile. Sometimes, however, the transparent cover is a liability in extreme HV conditions, so it is omitted or stripped off. You can find these zebra stripe HV resistors both bare and covered. Once bare, however, they often get chips in the resistive stripe if they are not handled with great care, as when stored side by side in a drawer.
I've never done this, but I've been told that one could make one's own high value, HV resistors, by painting on a ceramic rod with India ink. I suggest that you examine your resistor carefully for any chips/interruptions in the stripe. If your resistor is one of the bare ones, and you find a problem in the continuity somewhere, you might be able to bridge the gap with a tiny dot of India Ink.
If this HV probe is the style with the built in meter, you should also consider the possibility that the resistor is good but the meter has failed in some way. There could also be problems with the connections somewhere. Make sure you're barking up the right tree.
