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Old 7th Aug 2009, 10:25 am   #1
Boom
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Default Ekco A22 cathode bypass electrolytic

The A22 is coming along nicely, I've had to go for a total rewire including the IFTs and got some terrific wire from SWB18 which really looks the part and I decided to stuff the wax caps to try and preserve what I could of its internal looks.

I'm a bit stuck on the cathode cap' of the EBL31 (goes throught the chassis). Are these reliable enough to chance leaving in circuit? If not is it possible to restuff it? All I can see is a black cylindrical blob with no way in. I don't have a capacitance meter to test it with.

Dave
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Old 7th Aug 2009, 3:15 pm   #2
geofy
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Post Re: Ekco A22 cathode bypass electrolytic

Hello Dave, if the EBL31 is in a similar output stage as my Philips EBL1 then the cathode bypass is 25uF at around 25V and not likely to be to reliable any more but any up to 100uF will be ok. You could put one in place anywhere close after disconnecting the original.

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Old 7th Aug 2009, 3:20 pm   #3
Boom
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Default Re: Ekco A22 cathode bypass electrolytic

Thanks for reply Geof. I took a chance and put a 1/4" drill straight through the middle of it. The case survived and is now back in the radio stuffed with a nice new cap'.

Dave
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Old 7th Aug 2009, 9:00 pm   #4
David G4EBT
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Default Re: Ekco A22 cathode bypass electrolytic

Quote:
Originally Posted by David Tilley View Post
The A22 is coming along nicely, I've had to go for a total rewire including the IFTs and got some terrific wire from SWB18 which really looks the part and I decided to stuff the wax caps to try and preserve what I could of its internal looks.

I'm a bit stuck on the cathode cap' of the EBL31 (goes throught the chassis). Are these reliable enough to chance leaving in circuit? If not is it possible to restuff it? All I can see is a black cylindrical blob with no way in. I don't have a capacitance meter to test it with.

Dave
If it was the original cathode bypass cap, the black "blob" at the end is in fact as plastic disc. To take these capacitors apart, the connecting wires pass through a hollow brass rivet in the centre of the disc and are soldered to that rivet. If you desolder that, the disc can be carefully prised out, trying not to damage the rolled paper end of the capacitor outer tube. If you desolder the disc at one end, you can then pull out the innards at the other end.

Modern capacitors are puny in size by comparison, and when you put one back into the case, it's as well to secure it in place with a glue gun. Tie a knot in some 22 gauge wire connecting at each end and solder the wires to the capacitor leaving some slack in the capacitor wires, so that when the connections are made, you don't put a strain on the capacitor.

Make really certain you remember which end is which when you seal the case ends back on!

As has been said many times before, it's hopeless to simply test old electrolytics with a capacitance meter - they must be checked on an ESR meter. In the three A22s I've restored the cathode by-pass capacitors all measured 25uF, but all were infinity on an ESR meter. (It doesn't cost much to knock up a DIY ESR meter)

(Best to check the cathode voltage too of course, and the two resistors associated with the cathode (150/220R).

It's also not a useful guide to the condition of waxy caps on any old radio to simply check them for leakage on say a 20M Ohm range of a multimeter and assume they're OK. They're certainly not ok with 240V up 'em! They're as leaky as a runcible spoon. Never mind about just changing "THAT" capacitor, which has rightly achieved notoriety on this forum, unless they're very difficult to get at, change the lot!

Glad to hear you're A22 restoration is all but complete Dave!

David,
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