Re: PC board cap is a no-go

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Marry Krutsch by way of Terry Fritz <twftesla-at-qwest-dot-net>" <u236-at-earthlink-dot-net>

Hi Shad.

	Sorry about the failure.  I guess this hobby sees its share of those
:-/.  Anyway, what kind of cap are you looking for?  What capacitance,
voltage rating, etc. do you need?  I'm wondering because I've been
thinking of home-made caps lately and might have some ideas.

Have fun!
Winston

PS-How much wattage can your tube handle?  Just wondering... 


Tesla list wrote:
> 
> Original poster: "Sundog by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<sundog-at-timeship-dot-net>
> 
> Hi All,
> 
>    I was looking at etching the copper from PC boards and using them as
> elements of a flat stacked cap for the GU10A tube coil.  I *finally* got
> the chance today to set up a test.  12kv NST,  fullwave rectifier, and a
> variac on the NST input.
> 
>   It failed pretty miserably.  There was a lot of corona losses at the
> edges of the plates, even at ~11kvDC.  Puncture resistance was okay, but
> the sustained corona quickly weakened the dielectric enough for it to punch
> through after about 2 minutes of sitting at ~13kv DC (that'd be pretty hard
> on the GU10A).
> 
>    Yes, I could stack 2 plates together in series to halve the voltage
> across each one, but that would immediately quadruple the space needed, and
> also the cost.  Where before I'd need about 30 plates, I'd now need
> 120.  At around $4 each, it's now real expen$ive.
> 
>   So I need an alternate plan here guys.  I'm up the creek without a
> suitable cap.  MMC's are out of the question.   Too much capacitance, not
> enough current handling ability.  transmitting caps are hard to find and
> expensive, and I don't know of any home-made cap that will take the raw
> current (much higher sustained current than a TC can deliver).   I get the
> feeling LDPE and aluminum flashing caps would get too hot and disentegrate
> internally, leading to a spectacular and probably fatal (to the tube)
> failure.   I'm open to suggestions.
> 
> Thanks all!
> 
> Shad Henderson
> G3-1203