Re: toob coil

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

Original poster: "Malcolm Watts by way of Terry Fritz <twftesla-at-qwest-dot-net>" <m.j.watts-at-massey.ac.nz>

Hi James,

On 18 Mar 2002, at 16:30, Tesla list wrote:

> Original poster: "James by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<mustang3-at-cox-dot-net>
> 
> Hi All,
>      I was playing with my toob Tesla coil, and decided to put about 60 turns
> on the primary coil. I wanted to see if that would match the impedance of the
> primary to the toobs better. After some experimentation, I wound up with 31
> turns.  With 60 turns on the primary, it pulled a lot of current. The spark
> length was not good, even after tuning. I kept unwinding primary turns(and
> retuning) untill I got the best spark at the least current. The coil
tuned with
> 6Nf for the tank cap. The coil uses a uwave PS(1/2 wave doubler), and a
> modified MOT(secondary removed, rewound with 10 turns of #10 THHN wire)
for the
> filament transformer. It has two 500 watt triodes in parallel.  Secondary
is 6
> in. PVC wound with 26 in. of #27 and covered with West Marine System Epoxy
> glass. Pulls 23 amps. Max spark is 18-20 in. I suppose that the turns
ratio was
> too low with 60 turns primary. There is a fine line here. Too few turns
and the
> impedance of the primary is too low. Too many primary turns and the turns
ratio
> is too low. 

An easy conclusion to reach. Trouble is, you were also affecting the 
coupling which has a direct bearing on the reflected impedance from 
the secondary. And if the resulting discharges were different, that 
would also be affecting the impedance the tubes saw. Not trying to be 
picky but rarely are things so simple. It requires some deep 
consideration to design tests which measure the effect caused by a 
single changing parameter.

Regards,
malcolm

>    The Tickler coil is easy. Too few turns and the tubes run hot. Too
many and
> the "grid leak resistor" runs very hot. The tickler coil has to put enough
> voltage on the grid to put the tube into "cut-off". This is easy to see
with a
> scope on the tube's grid. Also, you can get an idea from the tube's chart.
>       I like playing with the toob coil. The drawback is that you are charged
> with RF. Everything you touch burns you. I end up with lots of little black
> spots all over my fingers. The uwave PS is quite dangerous. The 4000 volts at
> lots of current requires caution. I use absolute caution before touching the
> beast. Generally the "one-handed-rule" applies. Keep one hand in your pocket
> when it's live. 
>                                                                            
>                             Later,
>                                                                            
>                                 James
> 
> 
> 
>