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

[Dave Maples]

Charles: Can you put some meat on these bones, please?  How is "unacceptable
self-healing event" defined?  What were the test conditions (e.g. test
setup, capacitor value, etc.)?

Thanks,
Dave WB4FUR


-----Original Message-----
From: r-390-bounces at mailman.qth.net
[mailto:r-390-bounces at mailman.qth.net]On Behalf Of Charles P. Steinmetz
Sent: Thursday, April 25, 2013 1:31 AM
To: r-390 at mailman.qth.net
Subject: Re: [R-390] Orange Drop Caps vs Film Polyester Axial


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








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