See what'cha got started Lonnie!!! Well Tim, next to Brad Allen you are probably one of
the very few that has the original NOS parts in hand.
Let me say again, Bill is our expert here so if I'm off base with any of this he’s welcome to
correct me. Capacitors are notorious for not having an indefinite shelf life and are the
number one cause of problems in electronics. Electrolytic caps which are used as filter
caps inside the radio are especially bad because they use a semi-liquid or more often a
paste as the dielectric and they tend to dry out.
The capacitors used originally for noise suppression filters are dry paper capacitors. The
older ones used a paper dielectric where most now days are made with Mylar or some
other poly dielectric. But because they are dry doesn’t mean that they will last forever,
they are subject to moisture absorption and damp paper doesn‘t make a very good
dielectric. This results in a shorted capacitor, also the thin aluminum plates corrode
forming aluminum oxide which is non conductive. A paper capacitor doesn’t have to be
in service to go bad they often go bad just sitting on the shelf. I once bought a VERY
large cache of NOS Sangamo, Solar and Micamold molded paper caps. I thought I really
scored but when I got to checking them, not a one of them were good they had been
stored in an old open barn since the 50’s. when you broke them open the plates were just
white powder. Not all old paper caps go bad over time. I’ve seen ones that were kept in
dry conditions that still tested good after 50-60 years with no leakage and right on spec.
The later Mylar caps seem to fair somewhat better, but aluminized Mylar is still
hydroscopic and can hold moisture.
If you get a chance next spring Tim, I’d really be interested in seeing what the capacitance
of those original caps is that were in the kit. Any one of your physics prof’s would have a
simple hand held multimeter with a capacitance function on it, maybe you could borrow
one for an evening. It only took me about 10 minutes to pull the lead and measure the
ones on my ‘50 with a $25 Harbor Freight meter. I do have an HP 4262A LCR bench
meter that I use if I need a really accurate measurement.
Denny Graham
Sandwich, IL
Last edited by Denny Graham; 02/05/2012 4:48 PM.
