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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets. |
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22nd Nov 2019, 9:35 pm | #1 |
Dekatron
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 13,996
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Aerovox "chocolate" capacitors.
I call them 'chocolate' capacitors becaue to me they look like classic squares of a chocolate-bar.
There are a couple of them in my Pye PCR. One of them is 'that capacitor' between the EBC33 anode and the 6V6 grid. Are these 'replace-on-sight' like Micamolds, or can they be trusted? |
22nd Nov 2019, 10:59 pm | #2 |
Dekatron
Join Date: Feb 2007
Location: Leominster, Herefordshire, UK.
Posts: 16,535
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Re: Aerovox "chocolate" capacitors.
Poke it with a megger and see!
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22nd Nov 2019, 11:02 pm | #3 |
Banned
Join Date: Jun 2015
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Re: Aerovox "chocolate" capacitors.
I thought these caps are actually silver mica I may be wrong but I have never found any "dead'uns".
Joe |
23rd Nov 2019, 4:36 pm | #4 |
Dekatron
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 13,996
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Re: Aerovox "chocolate" capacitors.
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23rd Nov 2019, 4:57 pm | #5 |
Moderator
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Re: Aerovox "chocolate" capacitors.
I also think these are mica. The PCR is a military set (albeit for 'morale' purposes) and uses appropriate quality components.
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23rd Nov 2019, 5:16 pm | #6 |
Dekatron
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 13,996
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Re: Aerovox "chocolate" capacitors.
Yet it's stuffed-full of waxies. So I'm not taking any chances. (Despite providing them with a good breeding-environment my cache of CV510/511 output-bottles is not getting any larger!)
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23rd Nov 2019, 9:01 pm | #7 |
Dekatron
Join Date: Nov 2011
Location: Surrey, UK.
Posts: 4,394
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Re: Aerovox "chocolate" capacitors.
I think that the PCR was a 1944-on product? When the churn-'em-out-by-the-thousand expendable-performance philosophy had thoroughly eclipsed the pre-war "make me a dozen really well, here's a blank cheque" outlook. Hence the plethora of state-of-the-art electronics equipped with the likes of paper-dielectric moulded Bakelite capacitors for minimal unit cost and conservation of strategic materials- if it works till next year, it's a bonus. (Not to mention things like rocket-propelled interceptors made of plywood and devoid even of landing gear- but that's outside forum scope!).
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24th Nov 2019, 11:36 am | #8 | |
Dekatron
Join Date: Feb 2003
Location: Cottingham, East Yorkshire, UK.
Posts: 5,761
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Re: Aerovox "chocolate" capacitors.
Quote:
If it's low value, is in a tuned circuit, has retained its value, and passes a 'Megger' test, it's almost certainly mica. If it's a higher value - say above 500pF and is used for coupling purposes (as in your case) or in a bypass role, it's highly likely that it's paper. The two concerns are whether the capacitor is still fairly close to its stated value, and if it shows signs of leakage. If the desire is to leave it in place rather than to replace on sight, I'd check that it's retained its capacitance, and poke 250 - 500V across it with an insulation tester to see if there's any sign of leakage. This topic cropped up recently in another thread here: https://www.vintage-radio.net/forum/...10#post1189410 As the same encapsulation in the 1940s was used for both mica and paper capacitors it’s understandable that many will assume that if it looks like a mica capacitor, it probably is, especially when it carries the name ‘Micamold’ but that isn’t necessarily so. Higher values were mostly paper and have proved no more reliable over time than any other paper caps. The company simply use the same encapsulation for both mica and paper. Low value capacitance caps in tuned circuits (say up to 500pF) probably are mica, which have generally proved to be reliable decades later. They were invariably close tolerance and hold their value. Often (Dubilier for example) marked them ‘Mica’. Over 500pF, if used as by-pass or coupling capacitors of higher than .001mfd, even if they look like mica, they’re highly likely to be paper. It’s a topic that often crops up on the US Antique Radio forum: https://www.antiqueradios.com/forums...c.php?t=112157 'Micamold' is the name of the Micamold Radio Corporation' - not the structure of the caps. The war made it more likely than not that moulded paper rather than mica caps would be used in military equipment and the makers used that fact as a selling point. Page 78, ‘Electronics Industry’ August 1944 carried a full-page advert by the Micromold Radio Corporation entitled ‘The Facts About Molded Paper Capacitors’ in which they outlined the properties of moulded paper versus Mica capacitors. The advert emphasised the military use of the caps, with pictures of tanks, planes and soldiers. ‘Wartime equipment has definitely proven the ability of Micamold molded capacitors to function satisfactorily in by-pass, coupling and filter applications above .001mfd. As strategic mica is scarce Micamold Molded Paper Capacitors not only filled the breach but materially assist in maintaining the flow of equipment to the Armed Services’. I guess that the reason for the advert was to reassure those in industry who had doubts (well-founded as it turns out), that moulded paper caps aren’t as reliable as mica ones, the underlying theme being 'the armed forces are using our moulded paper capacitors to help win the war'. Source: https://americanradiohistory.com/Arc...es-1944-08.pdf Hope that's of interest and use.
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