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High Voltage Scope Probe 100:1 DIY Project

Foreword : classic 10:1 scope probes handle 200 to 400V depending on type and cost,
I work more and more with higher voltages, tube based equipment and such,
so i really need a good fast scope probe that will handle a few kV and also a few MHz
such scope probes are very expensive, but contain very few special parts, so a perfect idea for a DIY project

Here is my tested and trimmed in Schematic, i use 1 meter RG58 for my scope, incase you want to change that length
you need to adjust the value C6, longer cable = less C6

Simulation in LTspice match reality so that is great

PCB layout made in Altium, the holes under, and between components is to make capacity
as little as possible, and also low leak, since air is better than pcb

First try with no C6 mounted, ofcourse you know it will need a bit more to be correctly speed compensated

while i was waiting for my PCB to arrive, i 3D printed a "dummy" of the PCB with components
altium can export STL file of pcb including parts so that was super easy

This way i could get started testing the fit and assembly of the case 3D design done in Fusion 360

The two screws press and hold the RG58 perfectly tight in place

The tip is made from solid copper install wire, cut pointy for easyer to get better contact

Remember to configure your scope for 100:1 probe, now it read out the correct voltage,
ofcourse it will pick up a bit more noise specially visible in low voltage range,
like here only a 3v scope calibrate signal, this type of probe is of course NOT ment to be used for low voltage
so who cares about 0.5V noise :-)

FREE FILES:

BODY-BOT.stl 3D print file for the case

BODY-TOP.stl 3D print file for the case

Production_Data_hi_volt_probe.zip GERBER FILES

I have been using this probe for a year now, fixing a lot of high voltage stuff, and it is truely amazing
It uses 5 x 1kV rated resistors, so be sure your constant voltage is under 5kv
if you dare to get as high as 1.5kV for 2 sec pr resistor = the max official rating for the resistors
this means 7.5kv in total, I would recommend to use a scope you love a little bit less
maybe save an old scope from the trash next fleamarked :-)

see also here from 10 mins, this probe in action inside old tube scope
https://youtu.be/Rd1P4pAsqyk Oscilloscope Telequipment Serviscope Minor 1972 test teardown

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Thomas Scherrer OZ2CPU 2022
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