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Tesla schematic

Quoting James Peters <jpeters-at-enterprise.powerup-dot-com.au>:

 > Is it necessary to ground the primary? 

No.

 > In my plans it says to join one terminal from the transformer   
 > to the primary and then earth this wire. This means that one    
 > of the terminals becomes the earth. But I can't do that as my   
 > transformers are grounded at the midpoint. The only way I have  
 > been able to do this is to not use one of the terminals         
 > meaning I only  get 7500v. The only way I have been able to     
 > use 15000v is to not earth the primary coil. But this is        
 > unsafe. Is there any way I can earth the  primary but still     
 > get 15000v input?

I was wondering what was going on. You have been misled by the plans 
that is all. Common enough mistake. Set the plans aside and rewire 
the tank circuit as I have outlined below. 

Your neon has two high voltage insulators, or "bushings", as they are 
more properly called. You need to use both of them. 


    TESLA COIL SCHEMATIC                             ---------
                                                     |       | T1
                                                     ---------
                                                         O
         X1                              C1              O
                                         | |             O  L2    
           O-----------------------------| |-----        O
         ||O    |                   |    | |    |   L1   O
         ||O    |                   |           |    O   O
   -----O||O    * SG                *           |--->O   O
        O||O----*---|Gnd              G1             O   O
   -----O||O    *                   *                O   O
   120   ||O    |                   |                O   O
   Volts ||O    |                   |                O   O
           O-----------------------------------------O   O
                                                         |
                                                         |
                                                        Gnd

       X1 = Neon Sign Transformer, grounded center tap
       SG = Safety Gap. 
       G1 = Main system (tank circuit) Spark Gap.
       C1 = Tank circuit capacitor
       L1 = Primary Coil.
       L2 = Secondary Coil.
       T1 = Toroid discharge terminal                              
      Gnd = RF Ground.

I have deliberately left out bypass capacitors and RF chokes to show 
the correct circuit in the simplest form. Reading from the left to
the right, we start with the line in to the neon transformer. I am 
showing three leads leaving the transformer towards the coil. The
center lead is the internal ground on the transformer and case. 
The transformer case is grounded to the RF ground. A safety gap 
with center post is placed between the two high voltage bushings. 
The safety gap center post is connected to the RF ground and forms 
the ground reference for the high voltage circuit.

G1 is placed directly across the two high voltage bushings. 

C1 is placed in series with the primary coil.

Bypass capacitance is placed across the HV line, and RF chokes are 
placed in series with the HV line, between SG and G1 in this diagram.
(not shown for simplicity) 

The actual oscillator or "tank circuit" is the loop between L1, G1, 
and C1. This circuit, patented by N. Tesla, is the most fundamental 
RF oscillator known. Since the inductance is commonly referred to 
as "L" in circuit diagrams, and capacitance is commonly referred to 
as "C", this is known as an "LC oscillator". The loop between the 
inductance "L", capacitance "C", and the switch (in this case a spark 
gap) forms a "tank" where heavy currents can oscillate with low 
impedance. This circuit is properly called the Tesla tank circuit.
There is no need to "ring" or oscillate the tank circuit off of a 
ground reference. The tank circuit will actually ring better in most 
cases if it is allowed to "float" ungrounded. Any imbalance or kick-
backs will seek the center post at the safety gap for a ground 
reference, so the circuit is as safe as any.

The circuit given in your plans is for use with step-up transformers 
that have only one high-voltage bushing. You cannot effectively use 
that circuit with your neon power supply.

Give the tried and true circuit above a chance. You should be 
pleased with the results.

Richard Quick


... If all else fails... Throw another megavolt across it!
___ Blue Wave/QWK v2.12