He shoots, scores, sort of. No nothing but net here.
I wanted a time/phase accurate HV probe to look at the RF (well, it's a little supersonic if not really HF) on my ion generator. No such thing existed (s) commercially that would fit.
After one failed attempt where the silicone I used to seal the quartz tube the high value R was put into evidently contaminated all the insulators and/or the mineral oil I filled it with, this was try #2.
This time i strung together 10 10 meg resistors inside a rather larger 1/2" diameter quartz tube that happens to run parallel to a long "jumper' I have for when I wanted access to both the direct grid and the 50kohm/200w ballast resistor that used to be there... Both are insulated and also inside schedule 80 PVC pipe that has grounded brass screen wire around the outside.
Seems I got "lucky" here. The waveform ain't bad for 27khz square waves - here I used 40v of good old WWII-era GR pulse generator to drive the thing, and a rather nice new scope to look at the results. FWIW, I also used a B&K HV probe, which also looked somewhat OK but had far higher noise and was also WAY out of divide spec (the wrong load impedance?).
So, this one's off by around 5::1 on the high side - it's 100megs and 100k for the divider and ?? capacities but doesn't look too shabby here re timing = pure luck. It also has an unexplained DC offset.
My real signal isn't a square wave either, so the phase shift implied by the not-flat tops on the result might matter, I'll have to do more testing with this rig and of course in real life....
Here's some pix looking at the setup:
This last is trying to show the innards from the side...which never seems to work out that well due to the screen...I tried.
Now if corona or other meanies don't bite me badly, I can know just when things are happening on the ion grid, vs what I had which was a faraday probe not that close, with some differentiation no doubt along with the DC...and I can get real transit time measurements, better than the ones shown in eye candy here.
I think (hope?) I really lucked out here. With the official probe the noise was 100x greater and accuracy no better. But on the bench...waving a hand a foot away from this thing moved the attenuation at AC around way over 10::1....here at least it's inside a pretty controlled environment (other than maybe corona/ozone). Further tests will tell.