Old-Time Capacitor Tear-down

I had a couple of the original electrolytic capacitors from the Eico 950B remaining on the bench after replacing them with more modern capacitors.

It's important to replace these older capacitors, because they can either partially short, overloading your circuit with excess current, or completely short, potentially causing a fire.

I decided to take one apart and share what's inside.  It occurred to me after I was finished that the oily paper quite possibly had PCBs in it.  Whatever.  I've been exposed to it plenty of times in my youth, I'm sure, while doing the same exact thing with old electronics.

The sharpie pen is to show the size of these capacitors.  I took apart the red capacitor.  It was an 8 microfarad capacitor, rated for 525 Volts. For the record, I put both caps in the tester, and they were not passing DC current - both tested good.  That said, before I replaced these caps the max voltage the capacitor tester could reach was just under 440 DC volts.  After, it was 495 volts.

 I cut one end off, then de-soldered the lead on the other end.  This nasty brown thing came out, with a yellow glob of wax stuck to the far end.

Inside was a wrap of 3 oily paper strips, with 2 foil strips between.  The outer paper strip prevents the outer foil from coming into contact with the aluminum can.  The inner paper keeps the inner strip from being in contact with itself.  The middle paper to keep the foil strips separated.

 

Below is the entire stack of papers and foils, unrolled.  I had it weighted down at each end to prevent it from curling back up.  It had been curled up for over 50 years...

The two foil layers, obviously different materials, and the separating paper layer.   Interesting!

Cool diagram courtesy of www.sparkfun.com

I think maybe I will do a few posts on resistance, capacitance, reactance, and a few of the simpler circuits, because that's about where I'm at right now.