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toob coil



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. 
   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