Cossor 494AC Reservoir/Smoothing cap replacement

[gary_crutchley]

 Hi all,

 

I have a Cossor 494AC that I partially recapped a few years ago and use regularly. Recently I noticed a pronounced hum, inspection of the base of what is the original reservoir/smoothing capacitor confirmed a sizeable bulge and small crack in the rubber seal. The can was also leaking a small amount of electrolyte through the cracked base.

I have replacement capacitors on order and plan to fit them under the chassis rather than restuff the original can. I have replaced standard capacitors previously, but this is my first attempt at electrolytics so any tips and advice would be gratefully received.

Thanks in advance and best regards,

Gary

[Refugee]

Make sure you connect them the right polarity otherwise it will end up in tears.
Last time I did a double in one can I chose two that were slim enough to fit through the rubber bung side by side and drilled two holes deep enough. I put a dowel in the first hole to stop the remains of the old capacitor rotating while I drilled the second hole.

[Murphyv310]

Also remember to disconnect the old capacitor, so many forget to to this.
Ensure that the new caps are suitably voltage rated and the value of the reservoir capacitor is not hugely above the original capacitors value.

[ppppenguin]

Trevor's advice is good. If the reservoir capacitor (the one immediately after the rectifier) is too big it can harm the rectifier valve by causing surge currents that are too much for the rectifier. The smoothing capacitor (after a choke or resistor) has no such limitation. A bigger one may help to reduce hum.

[gary_crutchley]

Also remember to disconnect the old capacitor, so many forget to to this.
Ensure that the new caps are suitably voltage rated and the value of the reservoir capacitor is not hugely above the original capacitors value.

Thanks. I have ordered the same values and ratings as the originals, so it should be okay. My concern is of course to ensure that I connect them in the correct manner.

[ppppenguin]

When replacing electrolytics it's worth remembering that they have very wide tolerances. Rarely better than +/-20%, often as much as +100%/-50%.