[Collins] 75A-4 Recap
Eugene Hertz
ehertz at tcaf.org
Mon May 22 21:35:59 EDT 2006
On the subject of recapping and testing. I have a basic question. I have a cap tester that will show leakage in uA for caps tested up to 600v (sencore lc53). I have heard that ESR is what one should be looking for, somehow its a more accurate or telling measurement.
My question is, can't leakage and ESR be equated? For example R=V/I. Couldnt ESR be somehow derived from the leakage? Could ESR=600v/uA ?
Anyone shed some light on this subject?
thanks
Eugene
>-----Original Message-----
>From: Bonddaleena at aol.com [mailto:Bonddaleena at aol.com]
>Sent: Monday, May 22, 2006 02:39 PM
>To: geraldj at ispwest.com, collins at mailman.qth.net
>Subject: Re: [Collins] 75A-4 Recap
>
>In a message dated 5/21/2006 10:23:36 PM Eastern Daylight Time,
>geraldj at ispwest.com writes:
>On Sun, 2006-05-21 at 16:03 -0700, Kenneth Lopez wrote:
>> Howdy folks,
>>
>> Well, I've just acquired another 75A-4, just after selling mine.
>> These things seem to follow me home somehow! I guess I'll have to
>> keep this one...
>>
>> Serial # just over 1000, nice physical shape, some functional problems.
>>
>> First, where would one mount the blocking cap to take the B+ off the
>> filters? It is noted as C 144 on a later schematic. This A4 is early
>> enough not to have it installed. What type of cap should I use here,
>> disc ceramic?
>
>Disc ceramic or dipped silver mica would work well. I don't know the
>details of where to mount the capacitor.
>>
>> Next: I've seen the list of the "7 deadly caps" and note also the
>> need to replace the Black Beauties. Which others should I change?
>
>All the black beauties for sure.
>>
>> What is the preferred type of cap? Sprague Orange Drops OK for the
>> black beauties?
>
>Sprague Orange Drops are super for replacing the black beauties.
>>
>> It is working, but has pops, hum, etc.
>
>Pops can come from black beauties. Hum can come from electrolytics or
>from tubes. If 120 Hz saw tooth, its from electrolytics, if 60 Hz
>sinewave its heater to cathode leakage in tubes.
>
>> Probably need to replace the
>> HV mutli-section can. I see one at Antique Electronics. Expensive,
>> but the only ones I could find.
>
>Good electrolytics are those just recently made or formed. NOS
>electrolytics can be poorer than those in the radio.
>>
>> As I dig further I'll report nasty symptoms.
>
>After you replace the leaky paper and mica capacitors and the aged
>electrolytics, you should have few problems.
>>
>> Lastly, I am open to suggestions and guidance to bring this rig back
>> to spec.
>>
>>
>> Cheers,
>>
>> Ken N6TZV
>
>--
>73, Jerry, K0CQ, Technical Advisor to the CRA
>All content copyright Dr. Gerald N. Johnson, electrical engineer
>
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>
>Dr. Jerry has good advise, as usual. I use his high voltage methodology for
>testing caps and it works easier and better than my considerable collection of
> cap testers. I also found several bad mica caps in mine.
>It is always interesting to see a Black Beauty read perfectly correct (for
>it's value) on my NIST traceable cap bridge, but leak 350 volts of 400 volts
>applied to it! I don't even test old caps any more, I just change them to
>Orange Drops.
>The old girl performs excellently, now.....
>
>
>ron
>
>N4UE
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