[Boatanchors] capacitor tester

Tue Dec 7 22:14:56 EST 2010

I really like the ZM-11 bridge.  It is nice for testing electrolytic caps because its high voltage supply is derived from rectifying and filtering the output from an RF oscillator. You can increase to rated voltage while watching the leakage on the meter.   If the cap shorts or draws excessive current the load on the oscillator causes it to quit thus there is no smoke, explosion, or other undesirable outcome like you could get from using a "stiff" conventional supply.  A magic eye tube is used to indicate bridge balance for the various functions 

The ZM-11 also provides resistance testing including a couple of  very high ranges for insulation testing, measures inductance, and transformer turns ratio.  One of the neater pieces of vintage test gear out there.

Rodger WQ9E

----------------------------------------
From: "Carl" <km1h at jeremy.mv.com>
Sent: Tuesday, December 07, 2010 7:16 PM
To: "The Pollacks" <rinkies at att.net>, "'Dick KF4NS'" <kf4nsradio at verizon.net>, <boatanchors at mailman.qth.net>
Subject: Re: [Boatanchors] capacitor tester 

I seem to have collected a few myself.

One that is often used is a 1939 Sprague Model 16 which was renamed the TO-2 
in 1941. They are fairly scarce, sorta big, but prices remain under $50. 
They need a full recap and many resistors to become functional but modern 
components can give 1% accuracy. What I like about it is that there is a 
coarse step voltage switch which is fine tuned by a big wirewound pot unlike 
some later models which use just the pot which is a weak link and an odd 
value. The 10W WW stepping resistors are still well under 1% tolerance. 
Voltages up to 1000V are available which is why I like using it and it has a 
meter for voltage and leakage plus an eye tube for RC and insulation 
resistance. It does not discharge electrolytics. That was fixed in a later 
model.

I also have a TO-4 and TO-6A with the latter reaching very high prices 
thanks to the audiophools. Its an extremely good tester that isnt the size 
of some boatanchors..

And then there is the military ZM-11 which has enough controls on the front 
panel to satisfy an airline pilot. Naturally it does everything and they are 
generally in the $50-75 range.......so far.

I also used a 1941 Solar CE for awhile until the xfmr failed a few months 
after restoring it. It has an RF oscillator which is tops for checking micas 
in their intended enviroment and at rated voltages. Cheap but not often 
seen.

Carl
KM1H

----- Original Message ----- 
From: "The Pollacks" 
To: "'Dick KF4NS'" ; 
Sent: Tuesday, December 07, 2010 7:26 PM
Subject: Re: [Boatanchors] capacitor tester

>I am nowhere near a technical expert, but 4 cap checkers have followed me
> home and never left. (I've had others of the same model and sold them.)
> Here are my observations, and results that I've had.
>
> First, the IT11 and IT28, as you note, are identical except for the 
> cabinet
> style. I have both. I also have one of the C3 style, but so old that it
> doesn't even have a model number.  It's the old Heath light greenish brown
> with the maroon trim.  All of these work almost exactly the same way, and
> are about equal in accuracy, which is to say plenty close enough for our
> type of work, I think.  The drawback to them is not in measuring and 
> testing
> caps, but in re-forming electrolytics, one of my common uses.  The eye 
> will
> open when the cap is formed enough so that a sufficiently small amount of
> current leaks to show that the cap is formed and/or ok.  Usually, to form
> the cap, I start at about 25% of the rated voltage, and increase the 
> voltage
> slowly as the eye opens, which can take an hour or so, but usually much
> less.
>
> The problem comes into play when testing/reforming high capacitance high
> voltage caps.  The allowable leakage current is high enough to keep the 
> eye
> from opening even in a new capacitor.  The manual gives the formula for
> determining allowable leakage current, and a VOM in series with the cap 
> will
> tell you if the cap is in spec.
>
> The Sprague unit (I have a TO3 or 4, I forget which!) has a meter that can
> be switched in to read leakage current, as well as actual voltage, which 
> is
> varied by a rheostat continuously, rather than a switch with discrete
> voltages.  I don't know how much they go for, and I seldom see them for
> sale, although I haven't searched.
>
> Advantage of the Heathkits:  They're small and take up little room on the
> test bench shelf.  Disadvantage:  Above, with big caps.
>
> Sprague:  Only disadvantage to me is that it takes up too much room.  So, 
> I
> have a Heathkit IT-28 on the bench, and the Sprague on reserve when I need
> it.
>
> Hope this helps!
>
> Ron K2RP
>
> -----Original Message-----
> From: boatanchors-bounces at mailman.qth.net
> [mailto:boatanchors-bounces at mailman.qth.net] On Behalf Of Dick KF4NS
> Sent: Tuesday, December 07, 2010 3:38 PM
> To: boatanchors at mailman.qth.net
> Subject: [Boatanchors] capacitor tester
>
> I have a desire for an improved design tester for my bench. I have
> looked at the Heathkit IT-11/28 (don't see the difference between
> them) as a possibility and maybe Sprague TO-5/6A but they are so
> costly. I am now using the Heathkit C-3 which has been completely
> refurbished using Ken's (W7EKB) notes, with new parts and is in mint
> condition in functionality and appearance, but would like an upgrade.
>
> I will buy one of those Russian ESR meters when I save somemore
> greenbacks.  Please let me know your opinions and whatever you might
> have for sale. Anyone interested in the C-3 let me know.
>
> 73, Dick KF4NS
> St Petersburg, FL 33714 USA
> Keep The Glow!
>
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