Author Options:

Using a Vacuum Tube as a negative resistor in a Tesla Coil? Answered

Dear Sir/Madam,
My question concerns the posibilty of using a Triode/Tetrode/Pentode as a spark gap in a Tesla Coil. I want to know if it is possible to configure a simple circuit that will detect the volatge in the capacitor and discharge it when it reaches full charge.

I want to do this so that I can create a good impulse current in the primary and also because I want to make the tank ciruit efficient by eliminating losses through resistors and capacitors.

I have a GU 81m and a 12kv Vacuum Capacitor and a MOT as the power supply.

I would like to either use the spark gap style Tesla Coil circuit or create a relaxation oscillator. I know this is possible with a Thyratron but I don't have one just yet.

So the ciruit should operate as a LC ciruit and discharge the capacitor once no current flow towards it. I would prefer not to use a feedback coil.

Any help would be great.



I was cleaning my lab the other day look at what I found.

If you figure out how to do it use a tube that looks neat like these.



I know someone of merit who says he saw a 1.5" cube switcher handle 3 KW !!

Maybe that bottom center micro-dot in your pic is a New micro vacuum HV  Power switch.


Na that in the bottom center is a 2N3904.

It is the same power as the two RCA triode tubes.

Come a long way haven’t we.

I was thinking of using them to make a decretive prop that actually works.



4 years ago

Presumably you apply the nanosecond pulse of DC to the Tesla primary turns at regular intervals.
And you allow the primary coil flux to rise and fall or better reverse by some circuit means.

This flux change is necessary for transformer action to magnetically exchange high current
low  voltage primary for secondary high voltage low current.

The relaxation oscillator needs to operate near a coil resonance multiple which
needs to be at radio frequencies..

RF electrical current flows over the skin rather then through it making it NON-LETHAL.


4 years ago

As a young man over 40 years long ago
I used tubes in my early EE instruction in high school.

The first fact of tubes even Thyratrons is they operate on DC electrical power.
While a Tesla Coil uses AC resonance.

There are other facts But the first one is a killer.
There are other tube / Tesla limitations due to
  • Voltage
  • Current
  • Frequency
  • Plasma Tube Dynamics

Keep on theorizing :-)

  1. A pair of magnetron tubes, used in every microwave oven, wired in opposing parallel back to back should be able to handle the AC Tesla primary current flow.
  2. How to handle the filaments at the high opposing AC resonating voltages is left up to your ingenuity.  

Thanks for your feedback. I do have a magnetron but I don't want to use it because of radiation hazards.

In reference to the AC part I actually want to produce a nanosecond pulse of DC and run the Tesla Coil on that.

The reason I want an relaxation oscillator is it in more in sync with Tesla's original ideas and it is easier to tune.