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Echorec Multi-Section Electrolytic Capacitor Rebuild

If your Binson ‘Echorec’ delay machine still has an original factory electrolytic power filter supply capacitor installed than it will almost certainly need replacing. The reasoning behind this is that the electrolyte inside the capacitor slowly evaporates away over time, just like when the acid level drops in a car battery. However, unlike a car battery, it’s not possible to top up an electrolytic capacitor with water because it’s sealed.

As the electrolyte drys up the capacitor gradually loses its ability to hold charge and its internal resistance—equivalent series resistance (ESR) to be even more technically correct—increases. The changes in capacitance and ESR are drastic resulting in a significant degradation of filtering performance and in real terms this means increased mains hum breaking through into the audio circuitry. The capacitor needs replacing.

The Echorec utilises a two section capacitor for smoothing in its power supply. In the good old days multi-section capacitors were all the rage where several capacitors would be installed in one can, however they’re now difficult to find, expensive or unobtainable. Not to worry though—there are many people rolling their own multi-section caps. It’s quite easy to do and less expensive than buying a reissue or N.O.S. part and the performance will almost certainly be better too as today’s increasing demand for high power switched-mode power supplies means there is a wide selection of low ESR, high-voltage electrolytic capacitors to choose from.

Dried out electrolytic capacitor — How low can you go? Well, according to these measurements, very low—after 50 years this 47μF electrolytic cap now measures less than 1μF! - Photo taken by Greg Stoner

I chose two stubby little 47μF 350V capacitors as they were the right size to fit inside the aluminium can when stacked on top of each other. The can is easily disassembled by filing around the top lip where it is clinched around the plastic lid. Another method of getting into the can is to saw through the end with a fine jewellers saw. Bending the can is not recommended as it will distort it’s shape.

The plastic lid can be removed. Next the rubber O-ring seal needs to be pried out. It should then be possible to remove the contents from the can, a gungy, acidic mess resembling a lump of wet cotton wool—actually aluminium foil electrodes and dielectric that are the working part of the capacitor. It’s advised that protective gloves are worn when undertaking this work.

The inside of the can now be cleaned and is ready for installation of the capacitors. The negative pin of each capacitor should be connected together and they will need to be brought out of the top and connected to the can to make an earth connection. And that’s all there is to it. The rebuilt multi-section capacitor is now ready for installation in your Echorec.

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Echorec Multi-Section Electrolytic Capacitor Rebuild