[Milsurplus] Electrolytics then and now

[gl4d21a at juno.com]

Gang:

I followed the discussions (arguments?) of electrolytic capacitor 
vagarities with some amusement.  You realize, of course, that you are 
all correct, it is just that no one associated the pertinent time 
frame with their information.  The chemistry of electrolytics has 
undergone several radical transfrmations in addition to the ongoing 
product improvements.  Just take a look at (a picture of) one of the 
old 1930 wet electrolytics of 4 MFd. at say 250 VDC and compare the 
size of it with a modern capacitor.  There had to be some changes, 
not so?  Now, find a similar value device from about 1950 or 1960.  
Near halfway in between for size.  So, the change was not one big 
leap.  Look in your collection for an electrolytic about 10 or 12 
years old, and compare it with a 2006 production unit of the same 
value.  More size reduction.  Lots of new knowledge in chemistry and 
materials engineering in there.  

Back in the dark ages, when I was specifying electrolytics for mobile 
radio equipment, the capacitance values of standard units were +80/-
20%, and life was rated at 65°C at the operating voltage +10/-25%.  
You paid more for 85°C products, which we had to use because if the 
heat generated by a dozen or more firebottles in a closed box, and 
paid through the nose for tighter capacitance tolerances.  As was 
pointed out, few if any electrolytic applications require capacitance 
values which are more accurate than the available +80/-20%, unless 
you had an inexperienced circuit designer, and I have seen my share 
of those.  Monte Carlo reliability and performance calculations were 
just coming into use back then, so most of the designs I worked with 
were breadboarded with combinations of max/min values to discover 
problems.  Ah, the good old days.  Don't miss 'em a bit.

73,
George
W5VPQ


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