[Al (astral highway)]

Hey Albert,

That sounds like an annoying problem with the flashover. I can’t quite visualise what you mean - not between turns on the secondary at the top of the winding? Can you post a pic?

I’ve made five Tesla coils over the years. Yes, my first was Ulrich Haumann’s plasma tweeter using an old TV line output valve: small but beautiful!

The second was a design by John Freau using a Svetlana 572B transmitting triode, the typical microwave oven transformer doubled circuit and a simple cardboard postage tube coated with 20 coats of yacht varnish over the secondary winding . I got 22cm sparks in CW but the design was poorly tuned and could only run for 10 seconds without overheating the valve.

The third was a better design using a second valve and a better grid leak circuit and RF design. I took it apart when my son was starting to toddle around and left coil building until after a few years ago. He’s now a mid-teen and leaves all my work well alone.

My fourth was similar to your design, only with one GU81M. However I was by then really incapacitated by the multiple surgeries I’d unexpectedly had, which really limited how much I could safely carry and even a few Kg seemed a lot, suddenly. This really threw me as I was strong as an ox before they started dissecting and separating bits of my core and major leg muscles repeatedly in a short time!

I had ordered a bespoke 2.5kV, 2kVA, transformer wound by Ed, but when it arrived, I couldn’t even lift it off the floor as I couldn’t bend that far. (It’s 26Kg) . That’s now been bought by Chris on the forum, along with the valve and base and some huge caps for the power supply (collection pending).

Undeterred, I switched my attention to high-power solid state designs and with the overall rule that the resulting build should be modular, light and yet still spectacular.

My fifth was a small sub-project using a power MOSFET in a class E RF amplifier for about 40W of output

So I’m now on my sixth build. It’s slow progress as I have limited space in a flat after my marriage ended in 2012.

I have no dedicated workshop and have to do all cutting and fettling on a small picnic table on my balcony. Soldering and test equipment (‘scope, bench power supply, components) are systematically and in a logical order laid out on the dining room table and everything goes away after each session. You can imagine how this limits the pace a bit!

It might take me three days to get organised to build a simple assembly that would take 4 hours with a permanent workshop. However, I’m just delighted to be back in the game.

I’m also building some bespoke test equipment along the way and winding my own magnetics - this is complex and it’s often not possible to copy someone else’s design.

The purpose of the current build is linked to a big photographic project that I will describe in the future when I have made appropriate progress.

Hope to hear more from you soon!