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| Inexpensive Capacitor Leakage Tester |
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| jsi:
I've got a tube radio and a tube organ from the early 60's that I would like to make usable again. There are ample warnings on the net about how pretty much all old capacitors leak and need to be replaced. So I hacked together a capacitor leakage tester with my DC power supply and an old Simpson Model 374 microamperes meter. My power supply maxes out at 64 volts so I started testing some of the 100 volt capacitors in the parts bin. I was surprised how many of new, never used capacitors leaked DC current. Which brings me to the 600 volt capacitors in these tube devices. To test them I'm going to need more that 64 volts and that gets expensive fast! Heathkit IT-11 or IT-28 testers go for a small fortune and high voltage bench top power supplies are in the thousands of dollars. I want to test the replacement capacitors before I install them because these old guys were NOT designed with ease of repair in mind. Any ideas on how to test these high voltage capacitors without spending a fortune? |
| ogden:
I don't see reason why you would want to check specs of modern, band-new capacitors of reputable manufacturer which obviously you shall pick. |
| Cyberdragon:
--- Quote from: ogden on February 19, 2018, 02:50:45 am ---I don't see reason why you would want to check specs of modern, band-new capacitors of reputable manufacturer which obviously you shall pick. --- End quote --- They have infant mortality and can fail new. It's extremely rare though for good brand caps (I've seen it happen on Youtube though). For cheap caps, I'm not sure (just avoid them). |
| bitseeker:
Nice ammeter, jsi. Be sure to bring caps up to voltage slowly to minimize the risk of pegging the meter. If you want to get an actual leakage tester, don't limit yourself to the Heathkit ones. Many Heathkit devices go for too much money on eBay. It's also a good idea to get one that discharges the cap, either automatically or with a button/lever, prior to removal. Be sure to check local sources, too. I got a Sprague TO-6 locally for significantly less than they go for on eBay. If you're comfortable with high voltages (I assume so, since you're going to work on tube stuff), you could make your own tester. Have a look at the schematics in the operating/service manuals for some of the vintage testers. |
| Damianos:
--- Quote from: jsi on February 19, 2018, 02:33:26 am ---I've got a tube radio and a tube organ from the early 60's that I would like to make usable again. There are ample warnings on the net about how pretty much all old capacitors leak and need to be replaced. So I hacked together a capacitor leakage tester with my DC power supply and an old Simpson Model 374 microamperes meter. My power supply maxes out at 64 volts so I started testing some of the 100 volt capacitors in the parts bin. I was surprised how many of new, never used capacitors leaked DC current. --- End quote --- Electrolytic capacitors need some time to operate in specifications. In the datasheets, leakage current is specified, but also an initial time period to achieve this. So, when testing electrolytic capacitors, give them some time to reconstruct the insulating layer. --- Quote ---Which brings me to the 600 volt capacitors in these tube devices. To test them I'm going to need more that 64 volts and that gets expensive fast! Heathkit IT-11 or IT-28 testers go for a small fortune and high voltage bench top power supplies are in the thousands of dollars. I want to test the replacement capacitors before I install them because these old guys were NOT designed with ease of repair in mind. Any ideas on how to test these high voltage capacitors without spending a fortune? --- End quote --- For testing capacitors a low power voltage source is enough. Because a small high voltage transformer may be difficult to find, a voltage multiplier seems more convenient. Using a selector switch gives voltage steps/ranges. Another solution is to use a low power boost converter. |
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