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Michael A. Terrell

wrote:
"The self contain HV probes are easy to change polarity. Either
reverse the meter leads, or connect a small bridge rectifier between the
meter and the probe and ground lead. "

Not so fast. These things had a current detect function for the horizontal output TUBE (valve for those overseas). Now if you put a DPDT switch there and reverse the meter coil polarity that would work.

However, a bridge rectifier would introduce error, and that error would be greater at lower voltages. Many meter movement barely need a volt but a standard diode drops .6 of that. At scope cathode voltages which might only be like 2 KV or less, this is significant.

Not all of them have a current function. The bridge rectifier would
introduce a little over 1 volt error. There is a shunt in the ones that
monitor cathode current for the horizontal output. You have no need for
hat in a scope repair. The reason I wouldn't use the switch is that
there isn't enough wetting current, so after a few years it can start
arcing. Even at low current, you don't want to create plasma. Calculate
the current, through the resistor for the full scale range. It is quite
low to keep from loading the HV supply and affecting the reading.

--
Subject: Spelling Lesson

The last four letters in American.........I Can
The last four letters in Republican.......I Can
The last four letters in Democrats.........Rats

End of lesson. Test to follow in November, 2016

Remember, November is to be set aside as rodent extermination month.