IT-28 Cap Checker

[Bob Okas]

Hi Fred and the Group,

    Oh yes it can!!! I have an IT-11, essentially a gray version of the
IT-28. I had the same experience. The problem is that the voltage divider is
composed of carbon composition resistors, and we all know that these drift
high. If a resistor at the bottom of the string goes way out of tolerance,
the rest of the settings will be off. I would replace all of those carbon
comp resistors with modern carbon film or even metal film resistors to fix
it once and for all. FWIW, I just finished fixing up an old tube amp, and
wound up replacing every carbon comp resistor. Some of the 470K 1/2W 10%
resistors had drifted up to 660K. That's 40% high!

73,
Bob - W3CD

-----Original Message-----
From: Heathkit Owners and Collectors List
[mailto:HEATH at LISTSERV.TEMPE.GOV]On Behalf Of FRED HOLNAGEL
Sent: Sunday, January 12, 2003 2:27 PM
To: HEATH at LISTSERV.TEMPE.GOV
Subject: IT-28 Cap Checker


I have one of these fine gadgets but no manual.  I was forming a couple of
electrolytics from the SB-400 HV power supply. Got full opening of the eye
at 400 volts in a few minutes. At 450 volts, no way after several hours. I
then tried some NOS CD 475 volt can type and the same thing happens. I then
figured I'd measure the voltage at the terminals and found that at 400 volts
on the scale there was actually 500 volts and at 450 on the scale there was
560 volts! My line voltage is about 120V. It can't be one of the switched
resistors has changed value as the overage is there at all settings. This
might be prevalent in some of your meters.  Might want to check! Fred W7PRV

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