[R-390] Let me take a few whacks at that 'ole horse.
Ron Bussiere via R-390
r-390 at mailman.qth.net
Sat Oct 25 11:11:13 EDT 2014
I restore boatanchor radios and test equipment for 'fun'.
If you want to be well equipped for capacitor work, you 'might' need 3 different tools:
1. a tester like the TO-6A (I have a bunch of that series). This is necessary to test coupling/bypass caps for leakage at their rated voltage. ie: .01uf/600V or .1uf/600v
2. a bridge or a little hand held that will indicate value easily. A very leaky BBOD will usually indicate their exact rated capacitance with a small 9VDC tester. So, what are they good for? Measuring unknown caps like old variables, etc.
3. a ESR meter for checking electrolytics
Although I have a bunch of very competent cap meters like the Spragues, my go-to (leakage) tester on my main bench, is just a HVDC supply and an old VTVM. This was first described to me years ago by Dr. Jerry, the Technical Advisor for the Collins Collector Assn.
Works perfect. And almost as simple as me!! ha ha
Once I get a bucket full of BBODs I chuck them. Now, I wished I'd saved them and put them on ePay!!!
ron
N4UE
-----Original Message-----
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To: r-390 <r-390 at mailman.qth.net>
Sent: Sat, Oct 25, 2014 10:38 am
Subject: R-390 Digest, Vol 126, Issue 29
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Today's Topics:
1. Re: SSB Detector for R-390A. (Tom Frobase)
2. Megger and Capacitor Measures ... Good vs. Bad ? (Alan Victor)
3. Re: Megger and Capacitor Measures ... Good vs. Bad ?
(Craig Heaton)
4. Re: Megger and Capacitor Measures ... Good vs. Bad ?
(Charles Steinmetz)
5. Re: Megger and Capacitor Measures ... Good vs. Bad ? (Alan Victor)
----------------------------------------------------------------------
Message: 1
Date: Thu, 23 Oct 2014 15:43:21 -0500
From: Tom Frobase <tfrobase at gmail.com>
To: Bill <bmarx at bellsouth.net>
Cc: Radio Collins R-390A <R-390 at mailman.qth.net>
Subject: Re: [R-390] SSB Detector for R-390A.
Message-ID:
<CABYVeFVWLMkmn42D2E8tXfb66wTjHR502UHJSbL9ut+K+pH=Zw at mail.gmail.com>
Content-Type: text/plain; charset=UTF-8
Do you still have the unit? ... tom
On Wed, Oct 22, 2014 at 12:15 PM, Bill <bmarx at bellsouth.net> wrote:
> A number of years ago I wanted an SSB Detector for my R-390A. Jan Skirrow
> was selling kits for $155. I asked him for a completed unit but he did not
> sell them except in Kit Form. However he offered me a Prototype he had for
> the same price. The article he wrote can still be found at.
> http://skirrow.org/Boatanchors/TechTalk10.pdf
>
> Now with work and life issues I never got around to it, and it sat on my
> shelf.
>
> I offer it for $90 plus shipping. It is housed in a nice cabinet for
> another use.
>
> Bill Marx W2CQ
> ______________________________________________________________
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------------------------------
Message: 2
Date: Fri, 24 Oct 2014 17:08:56 -0400
From: Alan Victor <amvictor at ncsu.edu>
To: 390 list <r-390 at mailman.qth.net>
Subject: [R-390] Megger and Capacitor Measures ... Good vs. Bad ?
Message-ID:
<CAO-B_TetEP_gEkaFgFZUXeiSMrSUWCWoPQTiyYYmpx2LmCedeQ at mail.gmail.com>
Content-Type: text/plain; charset=UTF-8
I have been playing with a 500V Megger looking at questionable capacitors
in the R-390A. Somewhat of a challenge to determine is this really a bad
cap or borderline ok. After looking at a few known good caps, it became
apparent that a baseline for good versus bad would be useful. As it turns
out, this work was already done very nicely back in 1955 by a couple of
folks at the Diamond Ordnance Fuze Labs in Washington, DC. They plot the
MEGOHM x MICROFARD product for a variety of caps from the time, namely
mica, ceramic, paper, glass, and some poly plastics. At room temp, all of
these caps fall in the range of 4-6.2 (meg x uf ) product! Hence, a 47 uF
looks like about 100k ohm while a .01 uF should look like 400 -500 meg ohms
(infinity!). Handy to know and this is about what I saw on the Megger.
Their applied V is in this work was ~ 200 V. Curious if any of the folks on
the list have established a neat pass-fail criteria.
Alan W4AMV
------------------------------
Message: 3
Date: Fri, 24 Oct 2014 18:54:32 -0700
From: "Craig Heaton" <hamfish at efn.org>
To: "'Alan Victor'" <amvictor at ncsu.edu>, "'390 list'"
<r-390 at mailman.qth.net>
Subject: Re: [R-390] Megger and Capacitor Measures ... Good vs. Bad ?
Message-ID: <000601cfeff6$a00f1510$e02d3f30$@org>
Content-Type: text/plain; charset="us-ascii"
Hi Alan,
Four hours and no one has touch it yet, here goes.
Shortly after the first R-390/A followed me home, the question of good vs.
bad arose. Next step was a Sprague TO-6A capacitor analyzer purchase &
downloaded the manual from BAMA. You might want to take a look at the
manual, good reading.
Short version: One end of the capacitor has to be disconnected in order to
test. In other words, it (the capacitor) is half way out. Would it just be
easier to replace? If your receiver has those BBOD's, it isn't worth the
time messing with them. They are bad, duds, served their country well;
replace them with something newer.
Asking what type will start the capacitor wars here on this e-mail
reflector. The dead horse will be resurrected and beaten to death once more.
But the discussions are fun and sometimes a learning experience. Some type
of meat grease seems to have a calming effect afterwards.
Anyway, the BBOD's are way off in value and their insulation resistance
sucks wind. YMMV on other caps in the R-390/A. The 2MF oil filled paper &
foil cap, C551, in the IF deck has never tested good on my cap analyzer. The
insulation resistance is near zero! The blocking cap for the mechanical
filters should be replaced. Old electrolytic caps should be replaced.
After those are taken care of; get the darned thing back together, alignment
is next, work on bugs. In that order. Don't forget DeOxit on switches, etc.
Could be more, but you are making progress!
Regards,
Craig
-----Original Message-----
From: R-390 [mailto:r-390-bounces at mailman.qth.net] On Behalf Of Alan Victor
Sent: Friday, October 24, 2014 2:09 PM
To: 390 list
Subject: [R-390] Megger and Capacitor Measures ... Good vs. Bad ?
I have been playing with a 500V Megger looking at questionable capacitors
in the R-390A. Somewhat of a challenge to determine is this really a bad cap
or borderline ok. After looking at a few known good caps, it became apparent
that a baseline for good versus bad would be useful. As it turns out, this
work was already done very nicely back in 1955 by a couple of folks at the
Diamond Ordnance Fuze Labs in Washington, DC. They plot the MEGOHM x
MICROFARD product for a variety of caps from the time, namely mica, ceramic,
paper, glass, and some poly plastics. At room temp, all of these caps fall
in the range of 4-6.2 (meg x uf ) product! Hence, a 47 uF looks like about
100k ohm while a .01 uF should look like 400 -500 meg ohms (infinity!).
Handy to know and this is about what I saw on the Megger.
Their applied V is in this work was ~ 200 V. Curious if any of the folks on
the list have established a neat pass-fail criteria.
Alan W4AMV
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Message: 4
Date: Sat, 25 Oct 2014 08:15:20 -0400
From: Charles Steinmetz <csteinmetz at yandex.com>
To: 390 list <r-390 at mailman.qth.net>
Subject: Re: [R-390] Megger and Capacitor Measures ... Good vs. Bad ?
Message-ID: <20141025161530.FTi4oHmm at smtp11.mail.yandex.net>
Content-Type: text/plain; charset="us-ascii"; format=flowed
Alan wrote:
>After looking at a few known good caps, it became
>apparent that a baseline for good versus bad would be useful. As it turns
>out, this work was already done very nicely back in 1955 by a couple of
>folks at the Diamond Ordnance Fuze Labs in Washington, DC. They plot the
>MEGOHM x MICROFARD product for a variety of caps from the time, namely
>mica, ceramic, paper, glass, and some poly plastics. At room temp, all of
>these caps fall in the range of 4-6.2 (meg x uf ) product! Hence, a 47 uF
>looks like about 100k ohm while a .01 uF should look like 400 -500 meg ohms
Some data points (everything below assumes that the capacitor is
being measured at or below its DC voltage rating):
At 200v, an apparent leakage resistance of 100k represents a leakage
current of 2mA. What kind of dielectric did the authors test at 47
uF? An ordinary aluminum electrolytic of that value (not even a
low-leakage type), which should be the leakiest capacitor of that
value you can find, is specified at around 250uA maximum leakage at
room temperature (>35 megohm x uF). Any plastic film capacitor is
specified for leakage much, much lower than that (for example, WIMA
FKP3 metallized PP caps are specified at 500,000 megohms minimum,
while Series 225 Orange Drops are specified at 25,000 megohm x uF
product minimum -- 5,000 times better than the spec you
quote). Typical ceramics are specified at ~10,000 megohms.
5 megohms x uF sounds awfully low to me, even for 1955. It's also
*very* suspicious that caps made for tuned RF circuits (glass, mica,
ceramic), which need very low leakage to deliver high Q, didn't score
much higher than caps intended just to block or bypass DC (paper,
plastic). I haven't read the study (do you have a link?), but I'm
suspicious that there may have been systemic measurement errors.
In any case, it is my belief that a capacitor checker or megger is
entirely unnecessary for working on tube radios. Indeed, I'd go so
far as to say it's usually counterproductive because it is very often
used way too early in the troubleshooting process and focuses the
tech on individual parts when (s)he should be keeping an open mind
and looking at the circuit as a whole.
Note that most of the suspect caps in tube radios are (i) the main
filter capacitors (electrolytic in all but the oldest BAs) and (ii)
paper bypass caps on power supply lines and tube cathodes. Bad
bypass caps can almost always be found easily with a VTVM, since
there are invariably decoupling resistors between the raw power bus
and the bypass caps -- leaky caps will cause the local B+ at each bad
cap to be low. (If the radio no longer works (blows fuses or
smokes), then any leaky B+ bypass caps can easily be found with an
ohmmeter when the radio is unplugged -- they will generally read less
than 1k to ground.)
Best regards,
Charles
------------------------------
Message: 5
Date: Sat, 25 Oct 2014 06:49:59 -0700
From: Alan Victor <amvictor at ncsu.edu>
To: Charles Steinmetz <csteinmetz at yandex.com>
Cc: 390 list <r-390 at mailman.qth.net>
Subject: Re: [R-390] Megger and Capacitor Measures ... Good vs. Bad ?
Message-ID:
<CAO-B_Td4C9WUCcebGt__1ooxTd0H9LObuVTQRFyGHOMK=B2iqw at mail.gmail.com>
Content-Type: text/plain; charset=UTF-8
On Sat, Oct 25, 2014 at 5:15 AM, Charles Steinmetz <csteinmetz at yandex.com>
wrote:
> Alan wrote:
>
> After looking at a few known good caps, it became
>> apparent that a baseline for good versus bad would be useful. As it turns
>> out, this work was already done very nicely back in 1955 by a couple of
>> folks at the Diamond Ordnance Fuze Labs in Washington, DC. They plot the
>> MEGOHM x MICROFARD product for a variety of caps from the time, namely
>> mica, ceramic, paper, glass, and some poly plastics. At room temp, all of
>> these caps fall in the range of 4-6.2 (meg x uf ) product! Hence, a 47 uF
>> looks like about 100k ohm while a .01 uF should look like 400 -500 meg
>> ohms
>>
>
> Some data points (everything below assumes that the capacitor is being
> measured at or below its DC voltage rating):
>
> At 200v, an apparent leakage resistance of 100k represents a leakage
> current of 2mA. What kind of dielectric did the authors test at 47 uF? An
> ordinary aluminum electrolytic of that value (not even a low-leakage type),
> which should be the leakiest capacitor of that value you can find, is
> specified at around 250uA maximum leakage at room temperature (>35 megohm x
> uF). Any plastic film capacitor is specified for leakage much, much lower
> than that (for example, WIMA FKP3 metallized PP caps are specified at
> 500,000 megohms minimum, while Series 225 Orange Drops are specified at
> 25,000 megohm x uF product minimum -- 5,000 times better than the spec you
> quote). Typical ceramics are specified at ~10,000 megohms.
>
> 5 megohms x uF sounds awfully low to me, even for 1955. It's also *very*
> suspicious that caps made for tuned RF circuits (glass, mica, ceramic),
> which need very low leakage to deliver high Q, didn't score much higher
> than caps intended just to block or bypass DC (paper, plastic). I haven't
> read the study (do you have a link?), but I'm suspicious that there may
> have been systemic measurement errors.
>
> In any case, it is my belief that a capacitor checker or megger is
> entirely unnecessary for working on tube radios. Indeed, I'd go so far as
> to say it's usually counterproductive because it is very often used way too
> early in the troubleshooting process and focuses the tech on individual
> parts when (s)he should be keeping an open mind and looking at the circuit
> as a whole.
>
> Note that most of the suspect caps in tube radios are (i) the main filter
> capacitors (electrolytic in all but the oldest BAs) and (ii) paper bypass
> caps on power supply lines and tube cathodes. Bad bypass caps can almost
> always be found easily with a VTVM, since there are invariably decoupling
> resistors between the raw power bus and the bypass caps -- leaky caps will
> cause the local B+ at each bad cap to be low. (If the radio no longer
> works (blows fuses or smokes), then any leaky B+ bypass caps can easily be
> found with an ohmmeter when the radio is unplugged -- they will generally
> read less than 1k to ground.)
>
>
> Best regards,
>
> Charles
>
>
>
>
> ______________________________________________________________
> R-390 mailing list
> Home: http://mailman.qth.net/mailman/listinfo/r-390
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:R-390 at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>
Hi Craig, Charles and all.
Thanks for the inputs and information. It was not my intention to bring a
dead
horse back to life. In any case, I agree Charles on the troubleshooting
technique
you raise, while Craig raises a good point as well. However, if I find an
issue
with a circuit and circuit theory points to the likelyhood its this cap, I
would like to test it after removal with some level of confidence. If the
measure
says it's OK, as Craig highlighted, put a new cap in its place anyway.
However, I know
I have NOT found the problem.
Charles, on the numbers, I believe I mis-interpreted the plot scale. The
y-axis in this
paper reads LOG MEGOHMS-MICROFARD PRODUCT. As all the caps investigated in
this work had leakage
R values in the 10^10 to 10^15 ohm range, my error. So the plot figure 9 y
axis values are probably
10^4 to 10^6 (MEG-OHM x MF) in range. They reported mica and ceramic at
10^4, paper at 10^5 and the plastic
polystyrene etc... in the 10^5 to 10^6 range. No, they did not measure
large electrolytics.
There C values for measurement were 1000pF through .033uF. Applied V at
200volts. So the
47 uF I mentioned earlier should be ~ 85 M-ohms. Need to revisit what the
megger is reporting.
Incidently, a diode should be placed in series off the megger to the C
under test. If
you can't crank the generator with any constant rate, the C discharge back
through the
megger makes it hard to get a good reading. Charles, I am not in love with
the megger, but
seems like a reasonable tool for the job. If a cap is really bad, a simple
VOM can pick it
out. Its this borderline cases and the units that measure A-OK on an RX
bridge that are
potentially questionable.
The paper and plots were not found on line, but through a local libray
search.
It was published in '55 in the IRE TRansactions.
Thanks!
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