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Old 16th Oct 2017, 8:40 pm   #1
morgleman
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Default Advice needed on these capacitors

I am restoring a 1952 Ferguson 353 series Valve Radio.
It is working but I want to try and reduce the hum so am starting with replacing the Electrolytic Capacitors.
I need advice please.
I enclose photos of the ones already fitted. The brown one is a single capacitor 32 UF 450V
The top (silver) one is one item but according to the circuit diagram there should be two capacitor at 24uF each.
The layout drawing shows them both in the same position so there seems to be two capacitors in the same case.
Also there is no negative connection like the silver (double) capacitor. (don't know whether the capacitor case is the negative connection)
Did they make double capacitors and is the case the negative polarity
here are the photos
http://www.terrymechan.com/cappics.htm
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Old 16th Oct 2017, 8:51 pm   #2
frankmcvey
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Default Re: Advice needed on these capacitors

Hi, MM,

Multiple electrolytic caps in one can were common in vintage kit. In some cases, the can was isolated; in others it formed the negative connection. There was usually text on the can indicating which terminal was which - some manufacturers used symbols, others used colours.

New stock is available from people like AskJanFirst (Europe) and JustRadios (Canada)

For some reason, I'm getting a "Not Found" message when I try to access your photos.

Cheers,

Frank
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Old 16th Oct 2017, 11:01 pm   #3
'LIVEWIRE?'
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Default Re: Advice needed on these capacitors

I.too.am getting a 'Not Found' message when clicking that Terrymeachan link.
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Old 16th Oct 2017, 11:15 pm   #4
turretslug
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Default Re: Advice needed on these capacitors

Is it possible that the "24uF" capacitor is actually a 8 + 16uF double unit and the diagram is indicating these two paralleled for the 24uF? (A quick search on "Ferguson 353" brings up lots of stuff on tractors, but I'll confess to not having looked very hard so far). Double/multiple HT electrolytics were very common items from many manufacturers and the designer may have found this a cheap and convenient way to get the 24uF, or maybe there were just lots in stock from a previous or concurrent other model- not that the exact value is critical and electrolytics have a wide tolerance.

Not having luck with the photos, either.
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Old 16th Oct 2017, 11:36 pm   #5
crackle
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Default Re: Advice needed on these capacitors

Link to photos of capacitors. http://www.terrymechan.com/cappics.html

Mike
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Old 16th Oct 2017, 11:46 pm   #6
turretslug
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Default Re: Advice needed on these capacitors

Aha, thanks! Apologies, yes it really is 2x 24uF units in the one can, with each tag being the positive connection of one section and the can the common negative for both.
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Old 17th Oct 2017, 2:48 am   #7
peter_sol
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Default Re: Advice needed on these capacitors

Just fit 2 single 22UF caps at 350 0r 400vdc
you can expect some hum on those sets so how loud is the existing hum?
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Old 17th Oct 2017, 8:40 am   #8
'LIVEWIRE?'
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Default Re: Advice needed on these capacitors

It is possible to obtain dual can capacitors from sources such as those mentioned by frankmcvey in post #2. Replacing a 2 x 24uf with 2 x 32uf should be OK, the only proviso of which I know is that the value of the reservoir capacitor (the one directly connected to the rectifier valve's cathode), should not be greater than the maximum specified for the valve concerned.
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Old 17th Oct 2017, 9:39 am   #9
ms660
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Default Re: Advice needed on these capacitors

I would replace the filter electrolytic too (C23, 100uF) for the grid bias supply.

I note that V2 is reflexed for IF/AF.

Lawrence.
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Old 17th Oct 2017, 10:00 am   #10
HamishBoxer
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Default Re: Advice needed on these capacitors

If you wish to be closer value wise ,use 22uf 400/500V easily obtainable.
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Old 17th Oct 2017, 12:59 pm   #11
Radio Tech
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Default Re: Advice needed on these capacitors

Don't forget those waxie caps, and those that decouple. Good luck with the restoration though.

Ken
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