[Al (astral highway)]

Good morning folks. PROGRESS!!!

Please see pix.

1) First off, Richard (Mole42UK) has done an incredibly beautiful wind of the main inductor, the secondary coil. It is air cored and he lathe-wound it with adjacent turns, over the entire length of 41cm. It is wound on a PVCU tube.

It has an aspect ratio of approx 4:1 (length to height) and an inductance of around 25mH. DC resistance is 50R.

I'm incredibly impressed by Richard's craftsmanship. Richard used two pieces of circular stock to hold the coil in position and I will be able to use these to hold it in place on the base. It is also beautifully varnished to an incredible standard.

2) I finished work on the primary coil. This is the fatter coil at the base of the secondary. It took more work than is obvious - it contains metres and metres of 2.5mm dia single earth wire, with taps, and then at the top is the grid feedback winding. There is an anti-flashover guard between the windings, several turns of silicon sleeving with epoxy binding.

3) See pics showing a corona brush discharge at the top of the secondary coil. This is around 1cm long. The coil is just being driven by the MOSFET modulator I built specifically for test purposes. This draws 800mA at 30V for the result shown, so let's call it 20W RF in as the switch is nearly 100% efficient. The MOSFET runs completely cold on its tiny heatsink. Resonant frequency is 322KHz.

This is incredible, as the design frequency was 0.3MHz, and the plasma loads the coil (it has some capacitance). The Q is around 400.

Blue trace on scope, pictured, shows the waveform of the secondary coil. The scope probe is at x 10 and is hanging in the air a distance away from the coil. We can see that there is a zero volts crossing point: the rising edge of the sine wave is at the end of the MOSFET switching cycle. The MOSFET is still switched off, hence remains cold; it switches on with the rising edge of the sine wave. The phase locked loop is working!

As I say, this is only around 20W in. This is 50 to 80 times less power than the design power in, when the power supply and oscillator valve circuit are rebuilt. Hopefully, 50 centimetre plasma will be achievable.

Next steps:

This won't happen much before Christmas, but in the meantime, I will use the existing modulator to build an EHT power supply, already under construction, with an output again of only 20W or so.

Once I have the bespoke transformer back from Ed (Dinning), I will be able to do incremental testing of the valve power oscillator circuit.

Also pictured is an EHT probe under construction. This is following a design by Argus25 and should be good to 70Kv. It won't be able to test the voltage at the antinode at the top but it will be able to look at waveforms in the tank circuit (20KV plus at HF RF) and grid feedback circuit (800V plus).


I'm really happy to answer any questions!