[Boatanchors] Reforming Caps?

[LEE BAHR]

I might also add, the "paste" in the electrolytic is the stuff that forms 
the insulation between the two capacitor plates.  If the paste is dried out 
due to loss of moisture, the cap can loose it's insulating ability as well 
as it's capacitance will change.  With no insulating ability, it can either 
show "open", or short.  When it shorts, look out!.  In a bias circuuit, for 
example, look to see your final tubes melt down unless you happen to be in 
another room when it happens!  You can't reform an electrolytic which has 
been loosing moisture over time and if you can't reform it, look out when 
you try to use the cap.

Reforming an electrolytic is an art to some degree.  Watching how the 
capacitor reacts to the voltage applied to it as it reforms and how the 
current drops as it gets reformed all help the person reforming the cap 
understand to some degree how well the process is working.  (How fast, how 
much  and how low the current drops are good indicators as to how well the 
reforming process has worked).

Lee, w0vt




> Reforming caps is a hit and miss deal.  Reforming a cap is one thing, but 
> if
> it can be reformed is another thing.  Some electrolytics were made better
> then others.  In some/many cases the moisture has left the electrolytic 
> over
> time.  High grade electrolytics such as military grade caps seem to have
> survived better then others.  The temperature at which the caps were used
> and or stored plays a part too.  The bottom line is, reforming a dried out
> electrolytic surves no purpose.  Manufacturers of the caps had no 
> intention
> of making a cap last 50 years.  (I have smelled many NOS electrolytics 
> which
> are leaking, especially when many are close together in a box).  Today's
> caps are made better then those of old but the manufacturers today still
> don't put 50 year life on their electrolytics.  (More like 8 years).  Your
> budget, availability, and concern for original detail plus the time it 
> takes
> to replace a cap and the risk of what happens to the radio if the cap 
> should
> fail should all play a roll in how you approach replacing or reusing
> electrolytics.   I personally prefer to replace electrolytics whenever
> possible as I don't know how much moisture has left the cap over time.  An
> electrolytic that goes bad can do a lot of damage in many circumstances.
> But, as I said earlier, some of them were made better then others.  Many
> could be perfectly fine today, but how do you really know?  Many have gone
> bad too!  I like to play it safe in most instances by replacing them.  I
> sleep better at night.
>
> Lee, w0vt
>
>