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Re: Tube coils
Tesla List wrote:
>
> Original Poster: Michael Tucknott <Michael.Tucknott-at-virgin-dot-net>
>
> Hi all
> This may be a stupid qustion but here goes.
> Why is it that tube coils don`t use a torroid???
>
> Thanks in advance
> Mike Tucknott
> *********************************************************************
> If at first you don`t succeed......
>
> It must be someone else`s fault so
> Find them; Blame them; Make them pay
>
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Mike,
In general, tube coils which generate CW or 60 Hz modulated CW
subsequently DO NOT generate the extremely high output potentials and
simultaneous peak energies needed to breakout from the large radiussed
surfaces of toroidal toploads typically seen on most modern disruptive
discharge Tesla coils. A 1 kW vacuum tube Tesla coil might only be
capable of producing 150-200 kV peak voltage. A 2" diameter smooth
brass terminal is enough to completely stop the formation of corona.
Thusly a needle point is usually chosen to encourage breakout. In a
disruptive Tesla coil where a substantially larger tank circuit
capacitor is charged from the same 1 kW power supply for relatively long
periods of time and then discharged in tiny amounts of time, such a
disruptive discharge Tesla coil can easily hit peak voltages of 400 kV
or more.
It is possible to construct a vacuum tube TC that will break out from a
toroid but it takes a lot more power compared to its disruptive based
cousin, and the nature of the discharge is entirely different because of
its continuous duty cycle. One has to bear in mind the current handling
capabilities also in winding resonators (both pri and sec) for vac tube
TC's. Adding a capacitive topload to a CW tube coil quickly raises the
RMS circulating current flowing in the HV resonator which will quickly
overheat and melt a PVC form unless substantially heavier guage wire is
employed to wind the coil and handle the *continuous* current.
In one of my experimental tube coils I put a 3X20 inch smooth toroid on
top of a 6 inch by 30 inch PVC form that was wound with #14 AWG
enamelled wire. Using three 810 triodes with a DC input of ~1 kW the
secondary generated about 180 kV (measured) but would not breakout
although you could pull really impressive St. Elmo's Fire from a nearby
grounded wand.
The #14 AWG wound HV resonator got so hot that I feared the PVC form
would melt if I ran this machine for more than just 60 seconds. When
has anyone felt any heat at all in the #24 or #28 AWG wound HV resonator
of their 1 kW disruptive coil with massive topload? Its average power is
WAY LOWER even though its peak power is WAY HIGHER.
Robert W. Stephens