Hi Mike,
My neon sign transformer (NST) is putting out 30 miliAmps at 7.5 kV, end to end. There will only be half that potential from one end to the center tap, which will still work. In fact this circuit works very well using a MW oven transformer. There isn't any purple, but it still has the hot biphasic energy. With the MOT there's a lot more current, and a 10 gauge copper electrode from the T-tap will melt on the end, forming a bright red ball.
The pulse rate doesn't matter, since it will work with a single pulse. The purple color is a high frequency effect on its own. A diode, cap, and resistor can be used as a high frequency oscillator (the Testatica circuit uses that effect). So the resistance of the spark gap comes into play. But I have found that the color requires a certain number of miliAmps. A fence charger normally puts out 4 mA, and this isn't enough to get the color. But you might still get the T spark, and the associated static. At that voltage, you'd need three Oven diodes, which are good for 15kV each, with these diodes placed in series. It would be better if you could get a 1B3 tube. (Look for something in your collection with a top hat electrode).
This circuit should not be grounded, unless you're transmitting power to a water pipe coming out of the ground in the yard. (Kapanadze?) Even then, you can't ground the negative as that would kill the spark gap. And T-tapping it there would produce a redundant circuit branch, without the effect. The static is only transmitted while the circuit is running. However, when it's grounded to an isolated metal object, or one side of a capacitor, a residual static charge can build up. So be careful with that.
That's a very good idea about checking the power draw, with and without the T spark. I'm reluctant to take a chance, using my Watt meter. Electronic components do not always hold up with this static energy. Using my clamp meter to check the transformer's Amp draw would be another option.
And shunting across the diode doesn't prevent it from having something to conduct. Think of it as a parallel resistance, splitting the current. Also, I've been using that same battery, off and on, for a number of years, and it still reads 1.51V. I don't see any corrosion, swelling, or leakage. Although the negative from the cap contacts the battery, the return potential from the gap to the transformer doesn't. So there isn't any hV actually across the battery - just the static floating on the circuit. I've noticed in the past that a momentary biphasic spark next to an alkaline battery like this, in a wooden holder, will cause the battery to self charge, over a period of time. It's possible that something similar is happening here.
« Last Edit: 2021-10-09, 15:00:43 by Jerry Volland »
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