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Re: bought caps


From:	Malcolm Watts [SMTP:MALCOLM-at-directorate.wnp.ac.nz]
Sent:	Tuesday, November 11, 1997 2:01 PM
To:	Tesla List
Subject:	Re: bought caps

Robert, all,
             About the mica caps.....

> From:   Robert W. Stephens[SMTP:rwstephens-at-headwaters-dot-com]
> Reply To:   rwstephens-at-headwaters-dot-com
> Sent:   Monday, November 10, 1997 11:18 AM
> To:     Tesla List
> Subject:    Re: bought caps
> 
> > 
> > From:     Matt Mills[SMTP:megavolt-at-usa-dot-net]
> > Reply To:     Matt Mills
> > Sent:     Monday, November 10, 1997 5:47 AM
> > To:   Tesla List
> > Subject:  bought caps
> > 
> > Hi,
> > Managed to get hold of 5x 0.0005uF 5000v AC/7000VDC caps the other day
> > for free, i suppose their values are too low but if anyone knows
> > anyway for me to use them in a TC any help would be appreciated.  They
> > are made by sangamo and are MICA porcelain caps. They are rated at
> > about 10A.
> > 
> > Also most TC programs work out the cap needed for primary circuit
> > mine says for a 13kv/60ma tranny i need a 0.0147uf cap. but many times
> > I read about ppl adding more capacitance or changing theirs, so is
> > this not a fixed number or is this just the optimum for this supply?
> > 
> > 
> > Matt.                          mailto:megavolt-at-usa-dot-net
> > 
> > 
> 
> Matt,
> 
> Those caps sound fine for a very low power vac-tube TC if you place 4 
> or all 5 in parallel for the tank circuit cap (0.002+ mfd is a good 
> practical value for such a TC circuit).  Their voltage rating is 
> somewhat low however so your AC RMS from the 
> plate transformer should not exceed about 1500 volts though which means a 
> typical microwave oven transformer (~2000-2100 V) would likely blow 
> them up.  Several 811-A triodes would be a good choice to use at 1500 
> volts.  You could also use 805 triodes which are each approximately 
> the equivalent of two 811A tubes power wise.   Since your caps are all going
> in parallel the current capability of the entire bank will be increased.
> You could actually parallel quite a number of these tubes if you have a beefy
> enough power transformer.  You could use a microwave oven transformer if you 
> reduce the voltage to the primary to about 75% with a variac or fixed 
> transformer.
 
> rwstephens 

I have used them (foolishly perhaps) beyond their peak ratings in a 
disruptive coil. In fact, on occasions they suffered 50% over the 
peak rating although not at high rep rates. They are still going 
strong. In the end, I set the safety gap to about 15% over peak. 
Their robustness and discharge quality was impressive.

FWIW,
Malcolm