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 Post subject: inline cap checker
PostPosted: Sep Wed 04, 2013 6:42 pm 
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Hi,
I'm looking for recommendations on inline capacitor checkers. Want it for trouble shooting post WW2 radios already recapped. Thanks Jim


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 Post subject: Re: inline cap checker
PostPosted: Sep Wed 04, 2013 7:07 pm 
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Simple, just follow these steps:

Turn the radio on.

If it smokes, turn it off. A capacitor might be bad.

If it doesn't smoke:

If it hums a lot, turn it off, the power supply caps might be bad.

If it only hums a little, they may be okay, but if they explode in 10 minutes, they were bad.

If it doesn't explode, look at the audio output tube in a darkened room. If the plate is glowing cherry-red, the capacitor to the grid of that tube is probably leaky.

If the radio plays, but stations seem to "blare", the capacitors on the AVC line may be leaky.

Or you can do it by inspection-- if the capacitors are tubular, wax-covered, or plastic but more than 30 years old, they're bad. Maybe one out of twenty might be in passable shape, but why take chances. If it's a rectangular cap, it might be okay if it's silver mica, but many are paper and are quite bad.

The basic rule is, it's probably bad, unless it's a silver-mica rectangular, and even a good 25% of those are questionable.


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 Post subject: Re: inline cap checker
PostPosted: Sep Wed 04, 2013 8:35 pm 
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I want it for trouble shooting one all ready capped by a hacker


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 Post subject: Re: inline cap checker
PostPosted: Sep Wed 04, 2013 9:11 pm 
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Okay, if the capacitors look like they were made in the last 20 years, they're probably okay. The state of the art has improved and now settled down on stable, reliable insulating films like polyester, Mylar, and polypropylene. Electrolytics are better than ever, and except for a bad spell around 1999, they're really very good.

If the radio doesn't hum, and there is less than a tenth of a volt across the resistor at the grid of the output tube, and the radio picks up stations, and it doesn't "blare", the capacitors are probably in good shape.

But if you see any old black or wax tubulars, or bumblebee caps, or really any old tubular cap, it's probably bad.

As for "in-circuit" testing, that's generally impossible. Generally capacitors have enough circuit resistance across them to make in-circuit measurements inconclusive, or difficult to impossible.


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 Post subject: Re: inline cap checker
PostPosted: Sep Wed 04, 2013 9:13 pm 
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There is no such thing as an incircuit capacitor checker that is reliable.

Dave


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 Post subject: Re: inline cap checker
PostPosted: Sep Wed 04, 2013 9:28 pm 
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Location: Tucson, AZ
I use a Sencore LC103 which has helped troubleshoot in-circuit capacitors, but not common and too pricey these days. I would look into Peak Atlas ESR70 - Atlas ESR PLUS - Capacitor Analyzer. It is reasonable priced and includes in-circuit testing. I like the Atlas products, and have had good results with them. Review is here: http://www.youtube.com/watch?v=LZ49GCnf0V4 . There are a few other in-circuit models, that I read reviews on in the past, but can't comment on how well they work.


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 Post subject: Re: inline cap checker
PostPosted: Sep Wed 04, 2013 10:15 pm 
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jimz wrote:
I want it for trouble shooting one all ready capped by a hacker

What's the problem with it?
Also consider that the previous "restorer" may have not wired one or more caps in correctly. Do you have a schematic, to verify?

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 Post subject: Re: inline cap checker
PostPosted: Sep Wed 04, 2013 10:19 pm 
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Most of those capacitor checkers, even the $2499 ones, are useless in an old radio.

They work fine when you need to know whether the ESR of a 4700uF capacitor is 20 or 40 milliohms. That's important information ifyou're fixing up a PC power supply.

In an old radio, though, there's not much it can do for you. We KNOW electrolytics more than 40 years old are likely to be bad. We don't need to spend a penny of that $2,499 to find that out. Same for old tubulars.

Some of us have plenty of precision cap meters, like the HP 4260, 4270, 4282, a Heath "Q" meter, and a GR somethingorother bridge, all capable of displaying capacitance and ESR to three decimal places. Wonderful tools, but the numbers they give you are pretty much academic, we almost always already know, by that way the capacitor performs in a radio, whether they're good or bad. And the radio is a better test, as it tests the capacitor with the real mix of AC and DC voltages and currents, and only tests it to the extent needed in that radio.


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 Post subject: Re: inline cap checker
PostPosted: Sep Wed 04, 2013 10:35 pm 
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It would help this discussion if those offering advice said what characteristic of "a capacitor" was being 'checked' in their recommendations.

+1 Ancient_Hacker

Various measurements which are made on capacitors are:
C - capacitance value,
D - dissipation factor or
leakage resistance,
And Voltage Withstanding ability,
ESR - Equivalent Series Resistance

At least C & D can change depending on the voltage applied.

Any of these characteristics can 'go bad', but the way the radio (or whatever) reacts makes the difference of if it 'matters'.

One example; In a vintage radio, measuring the ESR and Cap value may not tell you that a capacitor is bad when leakage is what is giving bad audio output.

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 Post subject: Re: inline cap checker
PostPosted: Sep Thu 05, 2013 1:04 am 
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I have an old Sprague Kwik Test Cap Checker. Its more of a novelty than a serious piece of equipment these days. I use it every now and then on sets that have "newer" caps in them. Its generally right 60% of the time. We won't talk about the other 40% :wink: :lol: . For any real testing I use my Eico Resistance/Capacitance Bridge. Its spot on every time.

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 Post subject: Re: inline cap checker
PostPosted: Sep Fri 06, 2013 12:30 pm 
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The Eico 955 is a relatively common and inexpensive one. It is an interesting concept in that it uses the resistance in paralell with the capacitor to make an accurate measurement. From the schematic of the set you are working on, or from an ohmmeter measurement of the DC resistance across the capacitor, you set the unit to the expected RC ratio, and it will then tell you if the capacitance is correct or not. It's more work to use than the RF type of in-circuit tester, but when used properly it gives more reliable results.

Solar "Exam-Meters" and the Pyramid CRA-2 have RF in-circuit test capability, in addition to the normal bridge and leakage tests. The RF in-circuit test is done by connecting the capacitor under test across a coil in an RF oscillator circuit (IIRC, the CRA-2 operates at about 8 MHz). Both Heathkit and Eico made stand-alone versions of RF in-circuit testers; there were probably others as well. The cap has to have good "Q" in order for the oscillator circuit in the tester to oscillate; if the cap is open, shorted, or excessively leaky, the tester won't budge. But special short test leads are needed, and the range of capacitors that can be tested is limited (e.g. it doesn't work on electrolytics or very small capacitors).

Simpson made an interesting in-circuit capacitor tester, the model 383. This one contains a pulse generator which tries to "ring" or shock excite the capacitor under test. These testers are relatively uncommon, as they got a bad reputation for causing capacitors to fail soon after they were tested!

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 Post subject: Re: inline cap checker
PostPosted: Sep Fri 06, 2013 11:15 pm 
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Location: Bergen The Netherlands
In your case (fresh capacitors) an ESR meter is a perfect instrument to check C´s.
You have to know it´s limitations:it measures no small values or detecting of leakage in the wet ones.
For the rest,what you measure should be the same as the value printed on the C´s body.

Btw .Some comments here (and in earlier topics) give me the impression that not all
are familiar with modern ESR meters and/or their use in tube radios.

Jard N.


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 Post subject: Re: inline cap checker
PostPosted: Sep Sat 07, 2013 2:52 am 
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Modern ESR Meters? Don't have a clue. I have restored more tube radios than I can count and I did most of them with my trusty Eico Resistance/Capacitance Bridge among other tools. I'm certainly not against learning about them though.

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 Post subject: Re: inline cap checker
PostPosted: Sep Sat 07, 2013 4:37 am 
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I'm thinking that a modern ESR meter is aimed at about 1/1000th the ESRs we care about in an old tube radio. Optimized to measure milliohms instead of ohms. Not quite a good match as one might like. And we know by ear if the cap is bad, the radio hums. A free built in test equipment.


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 Post subject: Re: inline cap checker
PostPosted: Sep Sat 07, 2013 11:51 pm 
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Well I have and Eico 955 and 950B sitting on the shelf. Someone added to the 950B In Circuit Capacitor test circuit.
A folder came with the unit has schematic and info on added circuit. But it seems to only test for open or short. In the notes it refers to page 148 of "radio-tv experimentor fall 1962. Think I'll go through both of these and start using them.
Thanks for all your help.


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 Post subject: Re: inline cap checker
PostPosted: Sep Sun 08, 2013 1:09 pm 
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I think something needs to be said about the ideas behind in-circuit capacitor testing. Generally it is not possible to fully test a capacitor (i.e. measure its capacitance, leakage, and power factor if electrolytic) while it is in circuit. At least one end of the cap needs to be disconnected from anything else. So the idea behind in-circuit capacitor testers--including today's modern ESR meters--is to function as a go/no-go indication. They tell you if capacitance (or capacitive reactance, in the case of an ESR meter) is present, so you know the cap is neither open nor shorted. For troubleshooting a piece of electronic equipment, this is golden. It's the cap that is open or shorted that you want to replace!

At one time, small amounts of leakage in capacitors were considered normal and no cause for alarm. This is still true today for electrolytics. In bypass circuits, there are usually resistances in parallel with the capacitors. 8-megohms of leakage resistance in a screen grid bypass capacitor makes no difference at all if it is shunted by a 10,000-ohm bleeder resistor in the power supply circuit! Minor leakage could even be tolerated in coupling caps used in fixed bias circuits. Consequently, the inability to test capacitors for leakage in-circuit was not a limitation in most cases. Where it was is in AVC circuits and coupling to "zero bias" tubes like the 50L6 and 50C5. But in those circuits, it's easy to check the caps for leakage in-circuit with your trusty VTVM. In coupling circuits, a positive voltage on the grid side of the cap means it's leaky--assuming the tube you are coupling into is not gassy. AVC circuits simply won't swing negative enough when a strong station is tuned in.

The OP mentioned testing new capacitors in previously restored radios. This is a valid concern, and an in-circuit tester could be used to advantage. As others have already mentioned, there's little point in testing old paper and electrolytic capactors regardless of the method used. Electrolytics are subject to drying out, chemical changes, and internal corrosion. Paper is an organic material subject to molecular deterioration with age. Consequently, even if old capacitors test good and work initially, they will likely fail in short order, and depending on where they are in the circuit, they could cause a lot of damage to tubes and other components.

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 Post subject: Re: inline cap checker
PostPosted: Sep Mon 09, 2013 7:45 pm 
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Here's my review of some tube-era in-circuit cap testers (iincluding badwaxcaps' Sprague Kwik-Test) and others including how they work and their limitations.

http://www.ohio.edu/people/postr/bapix/captstr3.htm

-- Rich


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 Post subject: Re: inline cap checker
PostPosted: Sep Mon 09, 2013 8:44 pm 
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neutronic wrote:
Some comments here (and in earlier topics) give me the impression that not all
are familiar with modern ESR meters and/or their use in tube radios.
We know what ESR meters are.

We also know that vintage caps had no ESR specs, and the same is true of many modern caps.

You can't evaluate the condition of any component based on parameters that were never specified.

Of perhaps more importance is the fact that ESR is irrelevant in a 60/120Hz power supply.

ESR is of significance in switching supplies that operate with very high transient currents, or in
high-power discharge applications like strobes for photographic work.

People tend to recommend ESR for our applications because it's the "latest and greatest" glitzy test
available for caps, without regard to what it means and its potential significance in a particular design.

- Leigh

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 Post subject: Re: inline cap checker
PostPosted: Sep Mon 09, 2013 10:36 pm 
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Looking for an "in line cap checker" .... seems to indicate that you have a problem with the radio... and you are hoping that it's caused by a bad cap. So you want to use a device that will find the bad cap.

However... that's the wrong approach.

If you DO have a problem with the radio.. nothing beats doing some basic simple troubleshooting.
Things like measuring voltages and signal tracing.

Don't hope to find a bad cap by searching for a miracle "poke & hope" capacitor checker.
That's a waste of time.

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 Post subject: Re: inline cap checker
PostPosted: Sep Tue 10, 2013 12:42 am 
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Location: Long Island
Quote:
However... that's the wrong approach.

If you DO have a problem with the radio.. nothing beats doing some basic simple troubleshooting.
Things like measuring voltages and signal tracing.

Don't hope to find a bad cap by searching for a miracle "poke & hope" capacitor checker.
That's a waste of time.
Looking for an "in line cap checker" .... seems to indicate that you have a problem with the radio... and you are hoping that it's caused by a bad cap. So you want to use a device that will find the bad cap.


So what would you recommend? You've done your due diligence and have narrowed the problem down to one stage. Now what? Just "shotgun" it and replace all the parts, in the hopes of getting the bad ones in the process? Disconnect the caps and test them on a bridge, one by one? Remember, in this thread, the parts have already been changed and most will still be perfectly good. Properly used where it's appropriate, an in-circuit capacitor checker lets you rapidly home in on the defective component without tearing up the radio.

Quote:
We also know that vintage caps had no ESR specs, and the same is true of many modern caps.

You can't evaluate the condition of any component based on parameters that were never specified.

Of perhaps more importance is the fact that ESR is irrelevant in a 60/120Hz power supply.

ESR is of significance in switching supplies that operate with very high transient currents, or in
high-power discharge applications like strobes for photographic work.


Every capacitor ever made, since the first copper covered jars appeared in Leyden, has an ESR. ESR is related to power factor, dissipation, and tan-delta; if you have enough of the parameters, you can calculate one from the others. So one can use an ESR meter to check electrolytic capacitors for radio power supplies if one wants to.

But I agree that an ESR meter is probably not the first thing one needs for antique radio troubleshooting. Most ESR meters are designed to test large capacitors (4-uF and up), which limits them to power supply filters and maybe some cathode bypass caps. By the time those develop enough ESR to be objectionable, other faults like low capacity and/or high leakage are quite evident. Where an ESR meter really comes into its own is for troubleshooting modern circuit boards where there are dozens of electrolytics or tantalums, and you have to find the one or two that have burned out without unsoldering them all or cutting traces.

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