Saturday, July 2, 2011

Vintage Parts Excursion, Part 2: Capacitor leakage tester

Since my last episode with capacitor leakage it seemed necessary to cook up another piece of guitar amp specific test gear to complement the tube matcher I built recently, namely, a direct reading capacitor leakage meter and reforming device.

The original schematic was something I found In Alan Douglas' Classic Tube Testers and Test Equipment, but I've modified it a bit to suit local conditions, as it were.

It started out life as a Jackson model 645 vacuum tube voltmeter that had been lurking in the dark under my workbench. I didn't have a need for it but I couldn't bring myself to part with it-mostly because I like Jackson test equipment.

I'd been thinking about keeping it as is but it needed a special purpose 4.5 volt battery I did not have, so I proceeded to repurpose it. I built the power supply out of a Hammond organ power transformer and more terminal strips. They're great for prototyping things as they can be easily pop riveted in a convenient place.

At present it's been mocked up and I'm trolling through my resistor museum for combinations that meet the schematic value. And that's one good thing you can do with a lot of old carbon composition resistors is find ones that you can use.

In the meantime I ordered up a Russian military surplus analog 100 microamp meter that looks like reverse engineered Weston stuff-a fitting tribute to the men and women of Frelinghuysen Avenue.

I'll probably finish most of the wiring this weekend of the Glorious Fourth, and then station myself by the mailbox for the package from Estonia carrying my spiffy new Soviet microammeter.

Stay tuned.


  1. Nice Job, excelent!!. Do you think it works with a 0-200 uA meter?. it's the same think?, will be indicate from 0 to 100 uA only on the meter?. It can test any voltage capacitors?.

    Sorry for too many questions.

    Best regards.

  2. If you used a 200ua meter then you'd only get half scale deflection. Any voltage within reason I can get 600v out of it with a variac. There was a pretty big discussion on the antique radio forum, the test equipment one. The Russian meter is a dead ringer for an old Triplett. It was a fun project to build.

  3. hello, sorry for my bad English, I wanted to congratulate you on your post and its research work, beautiful equipment, while looking for a circuit to measure leakage ceramic capacitors, which his circuits recommend?, thanks in advance ...

  4. An insulation checker would work pretty well. I have a Shenzen Victor VC60B I got on ebay that will read resistance up to 2000 megohms and that'll tell you whether there's leakage in any capacitor, film or ceramic.

  5. Thanks Robert for answering, excellent tool, did not know him, I'll try to get it. A hug ...

  6. Hi Robert,
    If you still have Jackson 645 parts, I could use them all to restore mine.
    Thanks, Robert