Some guy posts his version of Mr. Carlson's LV Capacitor tester Ultra version...

[notfaded1]

Here's the video: 

I think this was built from Mr. Calsons design and updated with modern electronics... the video shows his schematic so maybe it has some hints on how the original one really worked?  Mr. Carlson himself said this to the builder:
Just fantastic work Yannick! Two thumbs up!

Perhaps this might help?  Or maybe this is settled already?

[notfaded1]

I just noticed he covered up some of the schematic... ugh!   

[notfaded1]

Some guys build of the original.

[WastelandTek]

It is only $2 to join Paul's Patreon and get legitimate access to his IP man.

[chris_leyson]

I would rather build the dangerous high voltage version and use an EM84 instead of the original tube. Bright blue flash, oops, there goes another one. Only kidding. But while you're at it why not build a grid dip meter and/or Wein bridge oscillator at the same time. There is a school of thought that says that low voltage leakage testing of high voltage caps isn't really valid because leakage current could be a function of voltage etc. If you're going to repair tube equipment it's not too much of a step to build your own test gear. Just saying.

[floobydust]

We already discussed the LV tester until the thread degraded into personal attacks due to flux fumes    https://www.eevblog.com/forum/testgear/mr-carlsons-lv-capacitor-leakage-tester!-it's-finally-out!/

Mr. Carlson does make some test gear that's extremely sensitive. You have to know how and when to use it. I feel that capacitor leakage current is not entirely a figure of merit, especially at this low test voltage. If I was working around paper and bumblebee capacitors on tube gear, I would use the old Heathkit tube cap testers up to 600VDC, Silicon Chip 2010 design went to 100V and another to 600V.  Pass/fail LED and how many uA would you use?

But why add an Arduino/LCD and stuff without the tester knowing what size the cap is?