In my continual quest for better, low priced test equipment I've been using an IRT-2 Insulation tester as described in an earlier post for determining whether capacitors-particularly the wax paper and foil types-are fit for continued use.
It's an important thing particularly in the case of plate coupling caps in the final stage of an amp, where a smallish amount of leakage-measurable in microamps-can shift the bias point of the tube enough to cause it to be seriously overworked-red plating is also part of the mix. The IRT2 has done a workmanlike job but suffers from the problems of analog stuff in that unless you can get the right range, the precision reading will escape you.
I started searching around and found a number of insulation testers on fleaBay, which range in price from inexpensive on the low end to ridiculously priced lab equipment. I didn't feel the need to pay for lab grade precision with lab grade prices.
Enter the Victor.
It's a digital readout insulation tester from the Shenzen Victor Hi-Tech Company with three test voltages and the ability to measure AC voltage up to 750-a nice feature.
For our purposes we're using the 250v, 500v, or 1kv ranges, and with the two position range switch we can read from 0.1 to 20 megohms or 20 to 500 megohms at 250v, 0.1 to 50 megohms and 50 megohms to 1000 megohms at 500v and at 1kv, 0.1 megohms to 100 megohms and 100 megohms to 2000 megohms-a substantial increase in range from my trusty IRT2.
It came in a nice box with a set of batteries (a big plus, in my opinion), test leads and alligator clips, a carrying strap, and a cover for when the device is not in use, and an instruction manual written in Chinese. It took a little bit of head scratching and a trip to the Shenzen Victor website (http://www.china-victor.com) to suss out the connectors and how to use the beast. However, the fit and finish is very good, the display is large and bright, lighting up on test, and the ranges are good for what my purposes are.
It's evident that the Shenzen Victor people put a lot of thought into this tester and did a very nice job at a good price, shipped for around sixty bucks. Rather than the generic QC passed white sticker this one came with a card with the part number and serial number, the date of manufacture, and the inspector's stamp on it in ink.
Here's an old Sangamo capacitor on test, showing a resistance at 250v of about 79 megohms give or take. At higher voltages, of course, the leakage rate is likely to be higher. Some work with my usual poly caps and some Orange Drops will yield a range of useful figures.
It's well worth the price of admission because you can also use an insulation tester to check transformer windings or any sort of circuit for high resistance shorts.
Props to the good folks at Shenzen Victor. They're doing a great job of putting serviceable, modestly priced test equipment in the hands of people like me.