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 Post subject: What is best Capacitor Analyzer?
PostPosted: Aug Wed 29, 2012 6:56 pm 
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I just missed a Pyramid CRA-1 on ebay. I have been looking for a Cap analyzer with reforming capabilities. How does the CRA-1 stack up against say the Sprague TO-5 or 6?

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 Post subject: Re: What is best Capacitor Analyzer?
PostPosted: Aug Wed 29, 2012 7:57 pm 
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I have an Eico 950B which works well for re-forming caps. You can usually find them on ebay for about $20. However, there are several schools of thought about actually using re-formed caps.

Dave


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 Post subject: Re: What is best Capacitor Analyzer?
PostPosted: Aug Wed 29, 2012 10:28 pm 
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The "best" would be homemade. The essentials are a low-current variable voltage supply and a 100µA panel meter. Additional ranges of 1mA and 10mA full scale are useful, although no usable capacitor will ever leak that much. The higher ranges are good for forming.

There's hardly any point to measuring capacitance with one of these old bridges, so all that stuff just takes up panel space.


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 Post subject: Re: What is best Capacitor Analyzer?
PostPosted: Aug Wed 29, 2012 10:46 pm 
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The CRA-1 is similar to the Solar CE capacitor analyzer. It's an RC bridge with an eye tube indicator, along with an electronic variable voltage power supply and VTVM circuit for insulation testing. The CRA-1 also has an RF "quick check" feature for testing capacitors in-circuit, something the TO-5 does not have. I don't have a CRA-1, but am quite familiar with the CRA-2, which is a slightly newer version that does away with the eye tube and uses the meter for everything. Either of the CRA's are fine capacitor analyzers and equal to the TO-5. Just don't try to use any of them on low voltage electrolytics, however. The TO-6 has lower voltage capabilities if you need them.

As for "reforming capabilities," any low current DC power supply that gives you the necessary voltages can be used for reforming electrolytic capacitors. However, much of what has been written about reforming in the past pertains to salvaging capacitors made with older dielectric formulations. These formulations would deteriorate after long periods in storage, resulting in excessive leakage current. If then subjected to full voltage, such capacitors could overheat and blow out. Reforming involves gradually raising the voltage, giving the dielectric layers a chance to reform, and the capacitors would be fine again.

Problem is, reforming started out with electrolytics which just needed a slow start at the outset, but were otherwise good. It does not work on capacitors which have dried out or which have internal faults like corrosion. Modern dielectric formulations do not exhibit such "memory" effects to any great extent. Consequently, capacitors with old formulations are likely to have other defects by now, making it pointless to reform them. Newer capacitors should not need it and probably won't benefit much from it.

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 Post subject: Re: What is best Capacitor Analyzer?
PostPosted: Aug Thu 30, 2012 3:47 am 
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So what do you want to do with this analyzer?

I have some thoughts on this - though if you were to look at my shop you'd quickly discern I favor the 'specialized tool' approach rather than 'combo' tools. While this means I have a lot of neat stuff, the tradeoff is I have a lot-of-stuff which sometime presents it's own complications :wink: My focus is clearly with equipment that contains high-voltage and tubes rather than LV stuff.

w/regard to cap reforming, I have succesfully reformed many caps using the approach described by Alan - having built and use an independent & variable hv dc power supply / monitoring for current in the uA and low mA range. As previously mentioned - the long-term value of cap reforming is questionable; though I have found it expedient to use reforming as means to get something up/running and then decide where to take it from there.

Not to dismiss an alternate re-forming instrument that many in this forum succesfully use: common service grade cap bridges (e.g. Eico 950, Sprague TO-series and the like). Big plus - they are relatively cheap/available and get the job done. Often they are a small project in themselves which is rewarding too. I have heard, anectdotally, that using the Eico 950 for this purpose can sometimes stress a hard-to-find component if the right technique is not used to de-power an electrolytic (iirc, a wirewound pot/ maybe someone on this forum knows more about that).

w/regard to ESR, there's plenty of threads on this forum that discuss different makes/models and their virtues. Easy to find discussion on ARF as that question seems comes up almost monthly. One recurrent theme I've observed: they are limited in usefulness for high-voltage caps, more useful for caps used in lower voltage such as switching power supplies and the like. As mentioned, since 99% of my interest is vintage tube loaded equipment, I've accordingly put off any interest in obtaining one.

w/regard to measuring capacitance value and characteristics, I can definitely recommend any number of vintage General Radio models. GR is highly regarded for it's line of impedance bridges. I have several though none that operate at RF frequencies. My goto for signal capacitor measurment and matching is the 1608 though I understand they are getting rather pricey. Other GR classics with slighly less accuracy; though good performers and more commonly found are the 1650(a/b), 640 (old but good) and the 740. Note none of these have any capability to reform capacitors. BTW-I do have a good working and calibrated Eico 950B...however I find the accuracy of cap measurement to be lacking (especially when interpolating between the dial marks).

Hope this helps.

Regards,
Grid2


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 Post subject: Re: What is best Capacitor Analyzer?
PostPosted: Aug Fri 31, 2012 3:23 pm 
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The "best" commercially at reforming and checking leakage? A Tektronix 576 semiconductor curve tracer. Works from zero to 1000v, lots of current available and checks leakage into the nA, great for checking leakage of those pesky ceramic HV caps in a scope's HV section. Of course, you don't measure values with it or play with ESR. Get a digital cap meter for values and an ESR meter for ESR.

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 Post subject: Re: What is best Capacitor Analyzer?
PostPosted: Aug Fri 31, 2012 3:53 pm 
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There is no best.

For those who enjoy wasting time in a futile reforming excercise Alans HB idea is fine. For a few dollars more an ancient prewar Sprague Model 16 (TO-2 after WW2) can be overhauled and used to check or reform any type of cap with its step selected 0-1000V section and the switched scale meter. Ive no use for eye tubes when doing this part as I mainly use it to test mica and oil caps at rated voltage, the eye is fine for reading values.

http://www.ohio.edu/people/postr/bapix/capchkrs.htm

Speaking of values if you rebuild a vintage tester with modern resistors and caps and match to 1% or less the accuracy is amazing and almost equals my HP digital LCR meter and handheld Wavetek.

Carl


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 Post subject: Re: What is best Capacitor Analyzer?
PostPosted: Aug Fri 31, 2012 9:21 pm 
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For a few years in my career, I repaired studio electronic strobes. We used B&K and Heathkit HV power supplies to reform the cap banks in units that were sitting up for a while. As far as an analyzer, rather then trying to restore an old unit, try taking a look at some older Sencores. They do about 90% of the later high priced units. Of the other 10%, the ESR testing of a cheap handheld unit is much better and generally not too useful in this application, but also make great low ohms meters. Many of the other functions of the newer Sencores are more production, data logging, and pass/fail oriented, none of what you'd need. Find an old LC-53 or one of the later LED display units that shouldn't cost very much and can do leakage test up to 600V and do up to a 200K uf count. The inductance measurements and test are also very accurate and useful for restoration work. It would be a better investment then an old, quality bridge that you'd probably have to rebuild and end up spending more then a working LC-53.

If you're really dead set on an analyzer or bridge, consider a working military ZM-11. They're a bitch to work on, but besides the standard bridge functions, they have full, built in capacitance testing and insulation testing functions. They can be had pretty inexpensively last time I looked.


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 Post subject: Re: What is best Capacitor Analyzer?
PostPosted: Aug Fri 31, 2012 9:52 pm 
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I have had both the Eico 950B and the Pyramid CRA-1 and the CRA-1 is the best of the two.
I got rid of the Eico 950B but kept the CRA-1, it is in storage.

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 Post subject: Re: What is best Capacitor Analyzer?
PostPosted: Aug Fri 31, 2012 9:57 pm 
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Location: Oak Hill, Virginia
Alan wrote - There's hardly any point to measuring capacitance with one of these old bridges, so all that stuff just takes up panel space.

I have an EICO 950 and thought that it's pretty good. I can test for capacitance value very quickly and also determine if it stands up at its working voltage. Yes it does not give me a number value for leakage current, but isn't the electron eye tube good enough? If I need to know the specific leakage current, I suppose I can include a current meter. Should I be doing that?

Clearly it's not a lab grade instrument, but is that really necessary to service a vintage radio where many components have fairly wide tolerance values?

Please help me understand why I need a better cap tester for vintage radios.

Tony L


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 Post subject: Re: What is best Capacitor Analyzer?
PostPosted: Aug Fri 31, 2012 11:34 pm 
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You don't. The eye tube is very sensitive on the paper -mica range. A few microamps will close it and there is no fear of burning out a sensitive meter.


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 Post subject: Re: What is best Capacitor Analyzer?
PostPosted: Aug Fri 31, 2012 11:53 pm 
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Just personal preference. I have a dozen bridges of one type or another, but the little hand-held thingie (I forget the name on it) is much more convenient for a quick measurement.

As for leakage, I have never used an analyzer with an eye tube because I built my metered tester about 40 years ago, before I owned any analyzers other than an ancient Tobe which never worked well. I just liked numbers, particularly when I was trying to get a feel for how much leakage was acceptable. I still like the analog meter.


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 Post subject: Re: What is best Capacitor Analyzer?
PostPosted: Sep Sat 01, 2012 12:16 am 
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I might be a bit of a hypocrite since I have a B&K 875A, ECG CX-920A, Sencore LC-53, Heathkit IT-28, Dick Smith ESR meter and a CD BF-50 cap checkers. I have many analog micro ampmeters and DC power supplies to do anything I want. But for a guy just into fixing up old radios a 950B will serve you well. I used one for years. They will check mica caps just fine and also can be used to find problems in tuning caps. I am a bit of a test equipment junkie but having the 950B on your bench and knowing how to use it can be all you need most the time for old radio repair.


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 Post subject: Re: What is best Capacitor Analyzer?
PostPosted: Sep Sat 01, 2012 4:20 am 
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As had been said, there really is no one best. It depends upon what your skills are and what your needs are. That said, my daily driver is an expensive Sencore LC-75 which I snagged at a resale shop for an excellent price. (shown at the bottom of the page referenced by Carl "Burnt Fingers".) It's so handy, I double check every cap I install. It has a special foot to hold down the leakage button for reforming.

But if I didn't have the Sencore, my favorite would be a Heathkit IT-11 or IT-28 (basically the same instrument). Those give the ability to set the three leakage indication points with precision for the typical dry caps, high voltage electrolytics, and a third category, low-voltage electrolytics. The bridge uses the lowest voltage of general purpose tube-era testers, amplifying the result. These also have the comparator/ turns ratio feature and have an input for an external generator such as a function generator for more accurate readings, especially useful for the turns ratio. While the voltage settings are stepped and not totally variable, paralleling with a voltmeter of decent sensitivity gives you all the accuracy needed.

http://www.ohio.edu/people/postr/bapix/CapChkr2.htm
At the bottom of this webpage, there is a pic of the two Heathkits along with the info needed to accurately set the leakage detection points.

-- Rich


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 Post subject: Re: What is best Capacitor Analyzer?
PostPosted: Sep Sat 01, 2012 2:17 pm 
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http://www.ohio.edu/people/postr/bapix/CapChkr2.htm
That's a marvelously informative pair of web pages on the ins and outs of the various models.


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 Post subject: Re: What is best Capacitor Analyzer?
PostPosted: Sep Sat 01, 2012 4:00 pm 
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There's a dark and dirty little secret to bridge-type capacitor testers, and that is, aside from minor frills and details, they're all essentially the same! Brand name and model don't make as much difference as it might first appear.

The basic analyzers measure capacitance and resistance at power line frequency. A bridge circuit is used with about 50 volts across it, so a single tuning indicator tube is all that is necessary for a display. Tests are included for power factor and leakage. Some units have meters for the leakage test voltage and current. Made by the millions by lots of companies such as Solar, CDE, Eico, Heathkit, PACO, Knight, and so forth. In good condition, one of these will do everything necessary for antique radio repair, and they are plentiful.

Better grade analyzers simply ramp things up over the basic units. An electronic variable voltage power supply is used for the leakage tests, and a meter is included for voltage and leakage. In some units, the eye tube is sometimes omitted and the meter is used for bridge readings too. The meter is often driven by a vacuum tube amplifier for greater sensitivity, at least on leakage. In a few units, a 1,000-Hz oscillator is available for measurements at that frequency, giving better sensitivity on smaller capacitors. The Sprague TO series, Pyramid CRA-1 and CRA-2, Solar CE, and military ZM-11 fall into this class. You may spend a little more money for one of these, but you'd be getting an "industrial grade" unit that is better made and somewhat more full featured than the hobby units mentioned above. However, since the basic design is the same, the industrial models are not necessarily any more accurate!

What do I use? If I am repairing something that uses tubes and has high enough voltage caps to withstand them, a ZM-11 or a CRA-2. If it's modern solid state gear, a digital capacitance meter and ESR tester. I also have several General Radio and Boonton lab grade bridges which can make more specialized tests for in-depth analysis of capacitors. Since those bridges don't test for leakage, a GR megohm meter that tests at 50 volts or 500 volts is kept handy for the purpose.

A couple other remarks. The reason the ZM-11 is the best capacitor analyzer on my bench because I test non-electrolytic capacitors in old radio or other tube applications first for leakage resistance. For electrolytics, leakage current and power factor. If leakage or power factor is excessive, there's no point in going any further. Generally speaking, I do these tests to QC the new capacitors being installed (not on old paper or electrolytic ones which are assumed to be bad already), on all oil capacitors regardless of ancestry, and on micas and ceramics when they are suspected of causing problems in a stage.

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 Post subject: Re: What is best Capacitor Analyzer?
PostPosted: Sep Sat 01, 2012 4:07 pm 
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The ZM-11 runs at 1 kHz.


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 Post subject: Re: What is best Capacitor Analyzer?
PostPosted: Sep Sat 01, 2012 8:37 pm 
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Location: Southern NH, 03076
The analyzers here are:

Sprague Model 16, TO-4, both from an ARF member; and TO-5, TO-6A from other web sites

Solar CE the first one I bought; $10 for shipping on ARF and needing hours of work

Military ZM-11, complete for $45 just from a Google search and showed up at an equipment dealer, works fine

I rarely use the ZM-11 as the Model 16 I find easier for silver micas, ceramic and oil filled caps. The others are just taking up space for now until I decide to put on Ebay.

Carl


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 Post subject: Re: What is best Capacitor Analyzer?
PostPosted: Sep Sun 02, 2012 12:37 am 
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I don't know about "reforming" unless testing the cap at it's voltage rating helps form it, but I got in the habit of testing new caps from stock after a lytic that was new was installed, shorted out in a piece of gear worth maybe 50 grand? and did some damage. After that I always tested same caps from stock. May have even turned up another defective one in the process, as I recall. The infamous red cap aluminum can type.


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 Post subject: Re: What is best Capacitor Analyzer?
PostPosted: Sep Sun 02, 2012 1:01 am 
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I have a Boonton 74C-S8 cap bridge. Its oscillator is capable of 100 KHz. I only have it because of an appreciation for Boonton stuff, not for its utility. It's not too often that I need to measure a cap less than 1 pF :wink: (or any cap to similar precision).

On the other hand, I do use Boonton/ HP Q-meters and the Boonton/ Measurements 59 grid dip oscillator frequently.

One caveat caution on any of the tube-era testers that use the split DC supply (early Heathkits, the Eicos, Lafayette, Knight kit etc.) Measure the voltage between the negative terminal and the tester chassis for your information. And keep that in mind when leakage testing or reforming an aluminum shell electrolytic. :shock:

-- Rich


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