[R-390] Orange Drop Caps vs Film Polyester Axial

[Charles P. Steinmetz]

Drew wrote:

>At issue is the self-healing action, which consists of momentary 
>short circuit between the capacitor's "plates", followed by 
>vaporization of a small portion of the very thin metal layer.  It 
>would seem that at some low voltage this would not occur, and so we 
>might use caps rated for, say, 800V in a typical receiver 
>application where the voltage encountered is much lower.  Would this 
>approach have merit?

My own tests, and those of others whom I trust, indicate that 
metallized film capacitors exhibit unacceptable self-healing events 
at impressed voltages of 200Vdc or less, regardless of their voltage 
rating.  On the other hand, unacceptable self-healing events have NOT 
been observed at impressed voltages of 50Vdc or less with metallized 
film capacitors rated at 50Vdc and above.  So, I use metallized film 
capacitors in SS designs but not in tube circuitry.

Best regards,

Charles