[Amps] How Do You Know When Filter Caps Begin to Fail?

[Eddy Swynar]

On 2012-03-28, at 7:23 PM, Bob K6UJ wrote:

> I had one blow years ago,  It blew the white debri all over the inside of the amp and 
> scared the &*%$#%$  out of me.  I was lucky and only the cap went.  My wife 
> came running in and wondered what the hell happened, she was not impressed :-)
> I decided to change all of them with new ones, hihi.
> 
> Anyone else have them blow and can share with us ?
> 


Hi Bob,

Back in about 1977 when I built my first linear amplifier & associated 1.5 KV power supply, I employed a collection of similar-looking (and very cheap!) surplus electrolytic capacitors that I bought from a mail order surplus outfit...

In those simpler days I had no idea of the necessity of "healing", or re-forming electrolytic capacitors gradually BEFORE use, & so simply applied full voltage to the string of them right out of the box, & basically "...let 'er go".

Each cap was an aluminum can type, with a wax plug at the bottom---the caps were mounted on a drilled piece of breadboard, with the wax caps (i.e. the bottoms of the cans) pointed upward...and for the initial testing purpose I had the top cover of the power supply off.

Well, within a second, or two, of applying B+ to the filter, I heard what can only be described as a shriek from a roman candle---and it grew in intensity. Suddenly a heard a spraying sound, whereupon I immediately killed the power...

Sure enough, the wax cap from one of the electrolytics had "popped", & electrolyte had spewed upward like lava from an erupting volcano, and actually stuck to the ceiling of my shack!

After that experience I brushed-up on the "...care & feeding of electrolytics", & to this day NEVER install ANY h.v. electrolytic cap without first going through the re-forming process with it...

~73~ de Eddy VE3CUI - VE3XZ