Re: Magnifier questions

Tesla List wrote:
> >From julian-at-kbss.bt.co.ukTue Aug 13 11:46:32 1996
> Date: Tue, 13 Aug 96 11:44:21 BST
> From: Julian Green <julian-at-kbss.bt.co.uk>
> To: tesla-at-pupman-dot-com
> Subject: Magnifier questions
> Dear All,
> This weekend I built a prototype magnifier setup, a small one.   Performed
> the tests in the living room on the coffee table.   I wound
> the primary out of 1/4" pyro (copper covered mineral insulated electric
> cable) 16 turns around a 6" daimeter former.  Held together with string and
> bamboo plant sticks.   The secondary is 150 turns of 0.56mm magnet wire on
> a 4" former.   The 1/4 wave resonator is from my TC and is 700 turns of
> 0.56mm magnet wire on a 7" former.
> The 1/4 wave resonator from the TC has resonant frequency of 220KHz
> when in a two coil system with 12" toroid.
> To tune in I had to put the tap on the primary on turn 16,
> which supprised me as turn 8 is used for a TC.  Had to remove the toroid
> to increase the resonant frequency to get better tune.
> I could only run the system up to 20% input power before the primary/
> secondary gap broke down.
> Power supply is 10KV -at-100mA
> Got 8" crona/sparks as output.
> My questions:
> 1)      Why do I need such a large primary?  Has the overall resonant
>         frequency fallen?
> 2)      How do you build a driver that does not break down?  Will dropping
>         the whole lot in oil help?
> Thanks for your help
> Julian Green


The magnifier requires a really special gap system.  The coupling between 
the pri/sec in a magnifier is about 8 times that of a normal small coil 
so breakdown between primary secondary is normal.  To prevent this, you 
can reduce the coupling a bit, drop the whole thing in oil or insulate 
with many turns of thick polyethylene sheet wrapped against the inside of 
the primary.  This wrap must extend well beyond the top of the primary 
almost to the top of the secondary.

Finally the tune on the primary is often the lumped tune of the secondary 
and resonator combined!

Richard Hull, TCBOR