Re: Tuning Isis and Osiris

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

Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>" <Esondrmn-at-aol-dot-com>

In a message dated 1/16/02 8:17:58 PM Pacific Standard Time, tesla-at-pupman-dot-com
writes: 


>
> Hi Nick, 
> I finally got the primary coils tuned in. 
> I connected the two primary coils in series with a 500 Ohm resistor and the 
> signal generator. I put my good Tek 2246 across the resistor. The coils are 
> spaced around 9 feet from eachother. 
> Tuning is from the bottom up with Cp. I'll send you an attachment if you 
> wanna 
> see the circuit. I spent several daze trying to dip the circuit with a RMS 
> digital mA 
> meter in place of the resistor and scope. I finally read the fine print for 
> the meter to discover that 
> the darn meter poops out at 100 kc. This was causing all sorts of spastic 
> parasites 
> and artifacts in the measurements. I also had the sig gen in parallel until I
>
> began 
> to suspect that I might be loading down the generator excessively. Learning 
> slowly. 
> I tuned the coils by clipping the leads from Cp onto the coil, using the same
>
> spot on each coil. I then adjusted the sig gen to find the arbitrary F res. 
> If too high, 
> I added Lp, and if too low, I removed turns. I kept twiddling until I zeroed 
> in on 
> the exact spot where F res for the primaries is 151 kc = F res for the each 
> secondary with its topload. 
> Can you find anything in all this where I am still screwing up something? 
>
> You were certainly correct when you said that tuning a twin coil is the most 
> gul durn 
> cantankerous thing ever. I thot it would be simple. Now I gotta put the beast
>
> back together and fire it up for the 100 inch sparks. 
>
> Q: 
> What's happening here? F res for EACH secondary is 151 kc. I have tuned the 
> two primaries in series and across Cp. That's how they are connected in the 
> twin. But 
> I have tuned the two primary coils in series so the TWO of them resonate at 
> 151 kc. Then we 
> are going to wrap each primary around its secondary with the two primaries in
>
> series 
> and across Cp. Is each primary resonating at 75.5 kc? The primaries are far 
> apart and the bases of the secondaries are tied 
> together and grounded to the power line ground. And to make things even 
> funnier, 
> We will have to find the electrical zero point by trial and error. All very 
> funny, I wish I understood the joke.      
>
> Happy day, 
> Ralph Zekelman 



Ralph, 

If I understand your design, the primaries for both coils are in series with
the primary capacitor attached to one end (or inbetween the primaries) and the
whole thing connected across the spark gap - correct?  Same circuit as one coil
except there are two primaries in series.  If this is the case, and each
secondary has a resonant frequency of 151 khz, then the primary circuit also
needs to run at 151 khz.  Basically, each primary will have one half as much
inductance as a normal single primary calculated to run at 151 khz with your
tank capacitor.  I would probably lay this out with the center of each primary
winding going to the spark gap.  Then the moveable primary taps each connect to
one side of the capacitor.  I can see how it would be difficult to tune. 

Ed Sonderman