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I know this isn't strictly slot related (although you can use it to check the rating and condition of resistors in a slot while they are in place).

I bought it because I like Bakelite items.
It's a 1940, portable(?) resistance tester made by Evershed & Vignoles (who still make resistance testers I believe). It's their 500v "Megger" type. Stands 6" by 4" by 2". Bare wires clip instantly into the two holes on either side; the generator handle folds over; you connect a resistor across the two wires and turn the handle. No matter how fast or slow you crank the handle the resistor (if it's not leaking) shows a solid steady reading which is, of course, handy when checking if a resistor has failed but also useful to determine the rating of a resistor that you can't read. Modern versions are, I suspect, smaller but doubt they work any better, look as good or are as much fun to use.

It's like mine... Had it years.... Megger

A word of caution: this is NOT a resistance tester, it's an insulation tester. Yes, it will give a reading of the resistance between two points, but to do this it chucks out 500v, which can be dangerous to both the user and the equipment under test when in untrained hands. If you want to measure resistance, get a multimeter.

Thanks for the update JC, my initial research showed it to be an insulation tester but I was put off by its description on radiomuseum.org which lists it as a resistance tester. Frankly makes more sense as an insulation tester, it will, of course, act as a resistance tester, and very accurately. Which is what they seem to be used for today as 500v is not suitable for modern insulation testing (so I'm told). Apparently these are still very much in use today, I read online that one company that re-calibrates meters gets on average 1 of these a month for re calibration so I guess they were very well made (as you might expect).

Yes! this is for testing electrical leakage currents between two conductors.
500v is still used today for this purpose.
In simple English, it tests the insulation between two cables. JC is correct, it is not a resistance meter.

coppinpr wrote: ↑Mon Sep 25, 2017 10:17 amI was put off by its description on radiomuseum.org which lists it as a resistance tester.

Actually they have it listed as an Insulation Tester. I updated the topic title accordingly.
There's a good page about its function and use here: http://www.richardsradios.co.uk/megger.html

Nice Bakelite!

I used to repair these.. Nice meter. Haven't seen a red one before, only black.