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Re: Text of 1964 article]



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<< From: William Noble <William_B_Noble-at-msn-dot-com>
 To: Tesla List <mod1-at-pupman-dot-com>
 Subject: RE: text of july 1964 popular electronics article on tesla  coils
(fw d)
 
 What bugs me about this isn't that the coil didn't work - I think I
understand 
 the tuning part now, what bugs me is that the cover of the magazine has a 
 photograph of the coil working.  So, it seems to me that I ought to be able
to 
 duplicate that, even if it's a crummy design.  - I'm using a commercial 
 capacitor, not a plate of glass, maybe that has something to do with it.   I

 did try the following experiments:
 
 1. added a metal toilet float to the top - small increase in arc, maybe -
hard 
 to tell
 2. wrapped primary around a vinyl sheet rolled into an 8" diameter tube, and

 spread the windings out to about 1/2 inches apart.  no change.
 3. tapped the primary (I wound 30 turns total) at turns 20, 15.  Small 
 improvement at turn 20, 15 about the same.  much better if I ran 1o turns - 
 e.g. turn 30 to turn 20.  about the same at 5 turns (e.g. 15 to 20).  At the

 smaller turns on the primary configuration, the secondary would arc through 
 the vinly (.30, two layers) to the primary from about the midpoint of the 
 secondary.  These arc were longer than I could draw off the top. This
confirms 
 to me that the coil is about twice as long as it ought to be.
 3. messed around with the length of the spark gap.  no effect - either it 
 worked or it didn't - tuning the arc was ineffective.
 
 I haven't tried giving the secondary a good ground - per my prev post, the 
 schematic has pri low side and sec low side tied together, so given that the

 CT of the sign Xformer is also grounded, this is impossible.  I will try 
 isolating pri and sec and grounding Sec low side to Xformer case and see
what 
 happens.
 
 I think I may also try making a plate glass capacitor exactly like the
article 
 - that (it says it's .00027) is about triple what my capacitor seems to be 
 labeled.  Maybe I'll also meaure my capacitor and see what it's value is - 
 since the label is corroded, I could have misread it.
 
 (and, yes, I'll make a half length secondary soon, but first, there is this 
 small matter of a trip to abu dhabi...)
  >>
William,

Sounds like you are making some progress.  You really aren't going to make a
lot of headway as it sits because it is so far out of tune.  If you cut the
secondary in half, you will still need a .006 mfd cap.  These are resonant
systems and just don't perform unless the tank circuit and the secondary are
in tune.  I would suggest making a new flat pancake primary out of 1/4"
copper tubing, 14 turns with about .30" spacing between turns and 6.0" inside
dia.  This will allow some room for tuning so you can add a toroid.  You
should be able to get 12" to 16" sparks out of this thing with a 12kv 30 ma
transformer.

Have fun in the desert.

Ed Sonderman






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