I would want to check the V7A schematic - it is easy to find probes with 1090 MegOhm resistor, if you are wanting to measure really high voltage. I am trying to resurrect my dad's IM-10, which calls for only 1 MegOhm resistor to make the scale settings read right without multiplying in my head. Apparently these are not so common. (Or at least not reported with generic "old HV Probe" ads on eBay!)