[Test-Equipment] [TekScopes] esr mETER dISCUSSION

[Richard Knoppow]

----- Original Message ----- 
From: <bonddaleena at aol.com>
To: <TekScopes at yahoogroups.com>; 
<test-equipment at mailman.qth.net>
Sent: Friday, July 23, 2010 11:37 AM
Subject: Re: [Test-Equipment] [TekScopes] esr mETER 
dISCUSSION


>
> Long post, but I hope it's helpful to someone!
>
> Hello to all. I have been following these "ESR" threads 
> with great interest.
> One of my first responsibilities when hired by IBM, was to 
> do some 'electronic reliability studies' of both IBM and 
> various competitors. For data, we had access to volumes of 
> manufacturing and field failure rates for some of IBM's 
> largest machines. To add to this, we had Mil-Spec failure 
> rates, Mfgs F/R, etc.
> It became quickly apparent, that electrolytic capacitors 
> were kinda short lived, and failure prone.
> About 15 years ago, my ham career of 35 years (at that 
> time), turned to "boatanchors", or tube type equipment. 
> Since I had a good job (and thanks to ePay), I was finally 
> able to afford the radios I could only dream about as a 
> teen.
> Over the years, I have restored hundreds and hundreds of 
> pieces of ham gear and older test equipment.
> After a visual inspection, and test of the tubes (if 
> present), the next thing I examine are the caps. Yes, 
> electrolytics and also 'bypass and coupling' caps. These 
> are usually in the .1 to .01 uf range.
> Initially, I also resisted the 'just swap them out' way of 
> thinking. However, the more I restored, the more I 
> learned.
>
> I have an old (1955) Collins receiver (75A-4, 22 tubes) 
> that's worth a bit. I really didn't want to just start 
> cutting and replacing, because they are highly sought 
> after collector items.
> This whole subject about replacing capacitors in old 
> radios is a LONG, and HOTLY debated subject. Some folks 
> say NEVER replace them, but the other camp feels that a 
> radio is meant to be used and enjoyed and should be able 
> to turn in it's best possible performance.
> Most of the offending caps are under the chassis out of 
> sight, but some 'purists' still consider it heresy to 
> change a bad cap. There are some that will agree that the 
> old caps are in need of replacement and will actually cut 
> open a tubular cap and put an "Orange Drop" inside!!!
> Once I started and found out just HOW leaky the old paper 
> caps were in my 75A-4, they all came out. Even one of the 
> Mica caps leaked. The radio needed a realignment but it 
> will hang in (with limitations) with some $3000 receivers.
> I still do not do a complete cap swap at random. It 
> depends on the vintage of the equipment. Older radios like 
> the Collins and Hallicrafters, etc from the late 50s to 
> mid 60s are PROBABLY gonna be candidates for a complete 
> recap. However, radios like a Drake, used more modern caps 
> and I have NEVER found a bad cap in a Drake radio, and I 
> own several dozen.
> Here's another example: I bought a Colins 51J-3 (18 tubes) 
> radio which was made about the same time as the 75A-4 or 
> maybe a year or two earlier.
> The 51J-3 has always amazed me with it's incredible 
> sensitivity and stability. One day, I decided to pull it 
> out of the rack and check it's caps. To my surprise, all 
> the coupling and bypass caps were 'dogbones' and 100% 
> perfect.
>
> Although I have a bunch of high $ commercial cap testers, 
> for small value (NON ELECTROLYTIC) caps, I prefer just a 
> HVPS and a good old VTVM.
>
> For electrolytics, I did a LOT of pondering and finally 
> purchased a Peak ESR meter. Works perfect! Self 
> protection, gives not only ESR but also value. I also have 
> a couple of analog ones, but the meter scaling leaves a 
> LOT to be desired.
>
> The following 'rules' work for me (N4UE):
>
> - caps in the .1 to .01 uf range (NON-electrolytic) 
> coupling and bypass caps MUST be checked for leakage at 
> their rated voltage! ESR can't be measured (at least not 
> on my test equipment) ha ha
>
> - bypass and coupling caps that leak 500+ VDC (out of a 
> 600 VDC rating), will still test exactly at their 'stated' 
> VALUE on any of my high $ LCR bridges.
>
> - DVM sized meters that have a 'cap' function will ONLY 
> tell you the value.
>
> - electrolytic caps should be tested with an ESR meter. My 
> Peak will sometimes measure simply tremendously high/low 
> capacitance versus the stated value.
>
> - electrolytic caps deteriorate with age. NOS caps sitting 
> on some TV repair shop shelf, will probably be NFG.
>
> - today's caps are orders of magnitude better than caps 
> from the past and much smaller to boot.
>
> - this size factor makes it easy to gut an old 
> multi-section 'can' electrolytic and stuff it with modern 
> replacements. Several companies provide this service for 
> those that can't 'do it themselves'.......
>
> - like a lot of things (!!), the old saying: "if ya don't 
> use it, you'll lose it", holds true.
> I periodically 'exercise' my collection.
>
> - of the thousans of caps that I have replaced, only 2 
> ceramic disks were bad (shorted) The old, wax covered ones 
> gotta go!!
>
> thanks fer the time and bandwidth!
> ron
> N4UE

     A couple of notes:  First, I've found that bridges 
which measure dissipation factor will often spot bad caps. 
Modern plastic caps have much lower dissipation factor than 
old paper caps did even when new. Modern electrolytics are 
better but the dissipation factor is not a whole lot lower 
than older caps that are in good condition.
     Dissipation factor is a way of measuring ESR but, there 
is also parallel resistance in a capacitor. Its not 
generally significant for other than electrolytic caps but 
is important there. Effectively, one wants to measure the 
insulation value of the dielectric. If its too low the cap 
will dissipate power and get hot, eventually failing plus 
its effective capacitance is lowered. Probably the best 
instrument for measuring this is a megger who's output 
voltage does not exceed the rated voltage of the cap. For 
high voltage caps this is fine because most meggers operate 
at 400V or 600V, both of which are standards for measuring 
insulation in machinery.  These work for any cap which can 
withstand the voltage.
     Mica caps can have problems which are unique to them. 
One is a problem with plated or "silvered" mica caps. The 
silvering can become oxdized causing the cap to become 
unstable. These really can't be spotted on measuring 
instruments but can cause all sorts of problems when in 
tuned circuits. Not all micas are of the silvered variety. 
Many older mica caps are made in stacks with interleaved 
sheets of mica and foil assembled under pressure. These can 
perform well but are subject to mechanical failure and 
instability. General Radio standard caps are of this type.


--
Richard Knoppow
Los Angeles
WB6KBL
dickburk at ix.netcom.com