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Old 06-04-2014, 10:19 PM
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Winky Dink Winky Dink is offline
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Heathkit IT-28 Cap Checker Question(s)

A few weeks ago I picked up a Heathkit IT-28 Capacitor Checker. I replaced nearly all of the capacitors and most of the resistors before I powered up. But I left an untrimmed resistor lead shorting the voltage control switch which wasn't so bad--only destroyed a 1-Watt resistor and a fuse and the smoke alarm didn't even go off. Beyond that the only hiccup was that the "power factor" potentiometer needed a good dousing with QD Electronic Cleaner.

I made that sound simple and easy, but it was actually a two-week struggle for me. Nevertheless, I'm now joyfully testing a pile of recycled electrolytics which I was previously afraid to use.

But!...the manual addresses the need to calculate a power factor to compensate for serial resistance in electrolytic capacitors. The manual is dated 1968. Is this an still an issue with modern capacitors? I've been ignoring the power factor and getting accurate results on capacitor values.

Also, the IT-28 has settings for (1) paper/mica/etc., (2) electrolytic, and (3) min. 'lytic ( miniature electrolytic). These settings are linked to the range settings, but it seems that the assumption is that paper is low uF, electrolytic is high uF, and miniature electrolytic is somewhere in between. Is there any need for the "min. 'lytic" setting? For that matter, are the electrolytic settings only because of the power factor control?

I'd appreciate some advice because I really don't want to figure out how to use the power factor.

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Old 06-05-2014, 11:15 AM
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NoPegs NoPegs is offline
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Generally you can just leave the power factor control at the lowest setting. If you come upon one that doesn't open the eye tube up as wide as you're used to, you can then adjust the PF control to see if you can widen it further. If you have to crank it much, it has a high internal resistance and for filter or pulse use should be considered for replacement.

On anything that is good (as in is very efficient with a low power factor) adjusting the PF control won't really widen the shadow any more, so I wouldn't worry about having to adjust it every time you check a 'lytic.
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Old 06-05-2014, 11:52 AM
Olorin67 Olorin67 is offline
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I think the min 'lytic might use a lower test voltage. So if you were testing transistor radio caps you wouldnt blow them. The earlier Heathkit checkers used something like 50 volts, which would be too much for caps in most SS gear.
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Old 06-05-2014, 03:28 PM
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That helps to explain what I've observed while trying to use the power factor control, and the comment on the "min. 'lytics" is in line with the leakage test instruction, "...the four voltage positions below 25 volts are to be used for miniature electrolytics only.

Thanks.
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