Gathering the gear for the new hobby

I'll need to buy some test equipment if I'm going to attempt repairs on electronic devices. So I've begun working on that.


 One of the more common failures in older electronics is capacitor failure.  Many older capacitors are of the paper type.  These were manufactured with two metal foil conductors, sandwiched between an oiled paper insulator.  Then they were rolled up into a cylinder and sealed.  This was done to maximize the capacitance surface area, while minimizing the volume needed for the capacitor.

Below is a cutaway of a paper capacitor.

 

Below:  A vintage rolled paper and metal foil capacitor.

Capacitors are used to block DC current, while allowing AC current to pass.  Some operate at fairly high voltages.  The capacitor above is rated for 400 Volts.  

However, as photographic preservationists are well aware, paper has historically contained small traces of acid.  Acid attacks metal, which the foil sheets are made from.  Once enough metal foil has dissolved and gotten into the paper, an electrical short circuit is formed.  Then unintended current begins flowing, and then you get failures - not only of the capacitor, but other components that supply the current.  Vacuum tubes, transistors, transformers, etc can be damaged by a failed capacitor.

Below, several vintage failed paper capacitors, with visible damage.  They don't always show damage.

More modern capacitors can also fail.  These have generated internal heat and offgassed.  the scored top is designed to fail first and release contents away from the circuit.

 

Because capacitors often pass DC current without showing visual signs of damage, I decided to get an old school capacitor tester.  The first one I bid on was filthy and "not tested" (AKA damaged beyond repair).  I lost that auction to someone who sniped it in the final seconds.  They overpaid a bunch!  Joke is on them!  I won a second auction at half the price for a clean, working unit!

This is an Eico Model 950B capacitor tester.  It can apply up to 500 DC volts to a cap and check for leakage current between the conductors.  The green tuning eye at the top right is how you tell if the capacitor is OK.  It's smaller than I'd thought it was - about 8" x 10"

Here it is with the lights out and the power on.

This one also came with a copy of the instruction manual, which the other auction did not.

And here we are with a couple of sweet pieces of vintage test equipment!