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"Floating" tank circuits

 > With a one bushing pig (only one isolated HV terminal) you are
 > forced into one of two possible directions: 1) grounded tank
 > circuits, 2) Running the core "hot" by placing the transformer
 > on an insulated platform.
 > 
 > The first choice really limits your selection of tank circuit
 > configurations, and my experience with grounded tank circuits is
 > that they are generally lower Q than floating tank circuits that
 > oscillate ungrounded.   Richard Quick

Quoting  "Jeff W. Parisse" <JParisse-at-DigitalDesignLabs-dot-com> 

> Is this what you mean by a floating tank circuit? Could this also be 
> refered to as a "balanced" tank circuit because two capacitors are 
> involved? Or would this be floating and balanced?...


                                            O
        (----------------|-----| |----|     (
        (                |    .25uf   |     ( ~750 Turns
------) (                |            |     ( 16ga. Heavy Build
      ) ( CT Grounded?   |            |     ( on 12.75" PVC form
      ) (------|         * Rotary     |---) (
      ) (    __|__       |                ) (
------) (     ---        |         6 Turns) (
        (      -         |                ) (
        (----------------|-----| |--------) (
                              .25uf         (
                                           __|__
                                            ---
                                             -

This circuit is both floating and balanced. Richard Hull calls it 
the "Equidrive" circuit, but "balanced" is a well understood term,
especially for those who have worked with this circuit using homemade 
capacitors that tend to drift in value during operation. This circuit
is rather tempermental when it becomes "unbalanced" during operation.

Remember, the actual tank circuit is the loop between C-L-G where:
C = pulsing capacitor; L = primary coil inductance; G = spark gap
(simply known as an "LC oscillator")

Tank circuits that do not incorporate an RF ground in this loop 
"float". When running floating tank circuits you should provide
a ground "reference". I strongly recommend placing a grounded 
center post between the two HV electrodes at the safety gap. This
provides a ground reference that will only be sought during over-
voltage conditions: kickbacks, flashovers, breakdowns, etc.. But
will not affect the tank circuit Q during normal operation.

The circuit below is an example of a tank circuit that oscillates
off of a ground reference. You cannot say that this tank circuit 
"floats" because the RF ground reference is right in the loop 
between the L & C in the tank circuit. The circuit below is 
typical of the type circuits you are limited to when using single 
HV bushing power supplies. You cannot run a balanced circuit with 
a single bushing pig... unless you hot core the pig, which I would 
put on the list of "NO-NOs" at pole pig power levels.


    TESLA COIL SCHEMATIC                              ---------
                                                      |       | T1
                                                      ---------
                                                          O
         X1                                               O
                                         G1               O  L2    
           O--------------------------->*  *<----         O
         ||O                  |                  |   L1   O
Line in> ||O                  |                  |    O   O
--------O||O               -------               |--->O   O
        O||O               _______ C1                 O   O
--------O||O                  |                       O   O
         ||O                  |                       O   O
         ||O                  |                       O   O
Grnded>    O------------------|-----------|-----------O___O
                                          |             |
                                          |             |
                                         ---          Ground
                                        Ground

There is a way to obtain two bushing power supplies from single
bushing pigs without rewiring: get two matched transformers, 
common ground the cases, then run the LV windings (our primaries)
in parallel with the HV windings (our secondaries) in series. This 
is both safe and effective. The wiring is the same as if you had a 
giant neon with no internal current limiting.

Richard Quick


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