Hello! I have been working on this project slowly for about 2 years now, and its finally coming together! Here are some specs: Power supply is two 700W MOTs wired in parallel with a voltage doubler(6uf cap). Its filtered with 2 russian 2.2nf caps connected in parallel, I honestly doubt they really do help in any way, but safety and common sence required me to put them in. The tube has a little filter on the anode, 22 ohms 15W wire wound resistor and about 23 turns of 1mm diameter magnet wire. The resonant cap is two 20kv 2nf caps connected in series, and the primary is wound with 2.5mm^2 wire, 39 turns with taps from the 24th turn upwards. The feedback coil is wound with 1mm diameter wire, 17 turns total with taps from the 12th turn upwards. Currently connected on the 15th turn. With the secondary I went a bit over board I think, its 2000 turns of 0.2mm magnet wire on 10cm diameter pvc pipe. It also has a little topload, about 9.4cm major diameter, 2.4cm minor diameter. Its a standard schematic with the grid leak connected to ground, and the tube is working as a triode. And the grid lieak circuit is a 910Ohm wire wound resistor and a 2nf 10kv cap at the moment. It was fine until i starded powering it with more and more voltage(Im not exceeding the limitations, its just that I previously powered it with half the line voltage). Something made a loud bang, there was a bright flash inside the chassey, and the poor tube died! I couldnt find the fault in the circuit. After doing a bit of research I found out that the tube I used (The Polish version, GU81 without the M) had a capacitor inside the bulb, so maybe that exploded? Later when cranking up the power there was a blue haze inside of the tube, it didnt seem to be gassy, but something was wrong clearly. I replaced the tube, and the same thing happened! The tube survived this time though, but I saw some blue discharges inside it for a second when tha fault happened. Only then I found out that the HV PSU transformer I was using at the time had some shorted turns on the secondary and there was clearly some arcing going on. But that couldnt have caused the loud bang or arcing inside the tube right? I replaced it with the 2 MOTs Im using at the moment, but Im still scared to turn the power up, I really dont want to kill the new tube! What could be causing these issues? What should I do to ensure I wont damage it?
I know the wiring looks messy on the photos, but in person it looks a lot nicer + of course I made sure no wires are touching for safety. Ive attached some photos for reference