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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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25th Jun 2022, 6:34 pm | #1 |
Triode
Join Date: May 2022
Location: Hartlepool, County Durham, North East, UK.
Posts: 28
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Repacking a capacitor can
I have a 32+32 350 v can on my tube radio and wanting to keep it looking athentic like it is now
The twist lock tabs i can de solder easy enough And the can has two terminals on it ones marked red and the other is not am i right in thinking the red is positive And the other is negative. Never repacked one of these before. This is on a eddy stone 840c I have replaced a few caps this week and was working fine and now the 32+32 350v can has failed |
25th Jun 2022, 6:41 pm | #2 |
Dekatron
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 13,956
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Re: Repacking a capacitor can
I;d suggest gutting the original can, leaving the eviscerated relic in-place if you really want to preserve the cosmetics [but honestly, do you spend your life gazing wistfully at your radio's intestines or actually use it?] and wire a couple of modern wire-ended capacitors on a tagstrip under the chassis to provide the actual functionality.
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25th Jun 2022, 6:44 pm | #3 |
Moderator
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,805
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Re: Repacking a capacitor can
A 32 + 32 uF capacitor is going to need more than two connections.
Usually the two negatives are connected to the can, and go to chassis via the lugs. The two separate terminals will be the positive ends of the two capacitors. One of these will be right after the rectifier and will have a hard life with the ripple current. To help it survive, it will be wound as the outermost capacitor so it gets best cooling from the can. I expect this to be the one with a marking. The other capacitor does further filtering after a choke or resistor. It has an easier life than the 'reservoir' directly on the rectifier output. So this capacitor is wound as the inner of the pair. It needs less cooling. David
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25th Jun 2022, 7:18 pm | #4 | |
Triode
Join Date: May 2022
Location: Hartlepool, County Durham, North East, UK.
Posts: 28
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Re: Repacking a capacitor can
Quote:
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25th Jun 2022, 7:27 pm | #5 |
Triode
Join Date: May 2022
Location: Hartlepool, County Durham, North East, UK.
Posts: 28
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Re: Repacking a capacitor can
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25th Jun 2022, 7:47 pm | #6 | |
Triode
Join Date: May 2022
Location: Hartlepool, County Durham, North East, UK.
Posts: 28
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Re: Repacking a capacitor can
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26th Jun 2022, 9:06 am | #7 |
Heptode
Join Date: Apr 2016
Location: Cheltenham, Gloucestershire, UK.
Posts: 872
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Re: Repacking a capacitor can
Hmmm .....
How do you know that the old one is dud - have you checked it's ESR? To retain 'originality' you have several options: retain the existing - if it's O.K.; attempt to reform the existing; replace the existing with a good new/NOS component [they are available]; or ...... gut the existing and re-build it with two new capacitors of contemporary design. The latter option will necessitate opening the can and warming-up and removing the existing contents - most people do this by cutting the can open with a pipe cutter and then taping the two sections back together using aluminium foil tape [preferably located and concealed behind any circular fixing clip/clamp]. All the foregoing notwithstanding - be sure to check the specified ripple rating of the existing capacitors - and match [or exceed] it when replacing with any other components. Cheers, D.
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26th Jun 2022, 10:13 am | #8 | |
Triode
Join Date: May 2022
Location: Hartlepool, County Durham, North East, UK.
Posts: 28
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Re: Repacking a capacitor can
Quote:
Its not retaining any voltage at all. Its dud. |
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26th Jun 2022, 10:45 am | #9 |
Heptode
Join Date: Dec 2020
Location: Swaffham, Norfolk, UK.
Posts: 582
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Re: Repacking a capacitor can
Just note if you re-stuff with modern replacement guts, don't pot them into place or in any way seal them in, they need to be able to vent, just in case the new ones fail.
As for the old ones being dud, is there a lot of mains hum from the speaker? it's not necessarily a sign they are dud just because they don't retain charge after switching off the set. |
26th Jun 2022, 11:42 am | #10 | |
Triode
Join Date: May 2022
Location: Hartlepool, County Durham, North East, UK.
Posts: 28
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Re: Repacking a capacitor can
Quote:
I'm going to replace it as it's over 40 year old on the safe side as for letting a new one vent i could put a hole in the can if i put replacemnt ones inside? |
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26th Jun 2022, 4:50 pm | #11 |
Nonode
Join Date: Jun 2007
Location: Coulsdon, London, UK.
Posts: 2,153
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Re: Repacking a capacitor can
Some people use two short capacitors stacked one above the other inside the aluminium tube.
Alternatively you may be able to buy tall, narrow capacitors that can be fitted beside each other. |
26th Jun 2022, 5:04 pm | #12 | |
Dekatron
Join Date: Dec 2004
Location: East Yorkshire, UK.
Posts: 3,964
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Re: Repacking a capacitor can
Quote:
John.
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26th Jun 2022, 5:34 pm | #13 |
Dekatron
Join Date: Feb 2003
Location: Cottingham, East Yorkshire, UK.
Posts: 5,739
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Re: Repacking a capacitor can
I always use Rubycon miniature high ripple rated electrolytics for re-stuffing cans.
Estimated life f 20,000 hours at 105 degrees C. I used to get them from CPC Farnell, but it's easier and cheaper on eBay for small orders, especially for postage. These 33uF 450V ones from a UK supplier would do the trick: https://www.ebay.co.uk/itm/284285226...id=EB55154708& You can see the spec at the link. (At his shop, you can see other values). I usually cut around the the can at the base, and when reassembling, use a circular strip of brass or aluminium sheet to join the can to the base with epoxy. The join is concealed with the mounting clip. A few pics attached. Hope that helps.
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26th Jun 2022, 6:53 pm | #14 |
Dekatron
Join Date: Oct 2003
Location: Croydon, Surrey, UK.
Posts: 7,550
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Re: Repacking a capacitor can
You can't go wrong with Rubycon. Been using them for years.
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26th Jun 2022, 8:42 pm | #15 | |
Dekatron
Join Date: Dec 2004
Location: East Yorkshire, UK.
Posts: 3,964
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Re: Repacking a capacitor can
Quote:
John.
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My favourite text message "I'll be there in five minutes, if not read again" |
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27th Jun 2022, 4:32 pm | #16 | |
Triode
Join Date: May 2022
Location: Hartlepool, County Durham, North East, UK.
Posts: 28
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Re: Repacking a capacitor can
Quote:
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27th Jun 2022, 4:35 pm | #17 | ||
Triode
Join Date: May 2022
Location: Hartlepool, County Durham, North East, UK.
Posts: 28
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Re: Repacking a capacitor can
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27th Jun 2022, 8:55 pm | #18 |
Dekatron
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 13,956
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Re: Repacking a capacitor can
Rubycon capacitors [and Panasonic] are good - so good that they are targeted by fakers.
I've seen quite a few capacitors branded "Rulycon" using a font which - coupled with a bit of convenient distortion of the printing on the plastic, could fool those who did not look too deeply. [Similarly, I've seen parts marked 'Bosgh' not Bosch] Take care out there!
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28th Jun 2022, 8:23 am | #19 | |
Heptode
Join Date: Oct 2019
Location: Täby, Sweden
Posts: 692
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Re: Repacking a capacitor can
Quote:
The before and after pictures are here, but I don't have a better photo of the 'after' to hand. |
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28th Jun 2022, 4:20 pm | #20 |
Pentode
Join Date: Sep 2011
Location: Coventry, West Midlands, UK.
Posts: 211
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Re: Repacking a capacitor can
The capacitor in my 840c is dated 1966 and is doing just fine. I did reform it two years ago, as it had been out of use for sometime, but it probably wasn't necessary. Its capacitance and esr. tested ok. It has an easy life as the HT is only 120V, and there's a lot of resistance in series with the rectifier, which is slow to heat. I replaced all but two of the small resistors 30 years ago, as they'd gone high, but most of the capacitors are original.
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