Hello Radu and a3an0,

I am facing similar issues with the 1.2 kit. I had the PCB printed by PCBCART and parted the BOM myself.

Using mostly no-name Chinese components (I have since learned my lesson about component quality…) I had low voltage across the tube (around the 200V arena).

I first attempted to fix this by replacing the MPSA42 (with this https://www.mouser.com/ProductDetail/610-MPSA42). The voltages improved to around 300-340V but still not getting the desired 380V.

Next I considered the inductor, my no-name one turned out to have 22 ohm resistance. I replaced it with one having 4.5 ohm resistance (https://www.mouser.com/ProductDetail/815-AIAP02222K). The tube could finally reached 380v however there is a lot of instability and duty cycle is high.

I fear that the readings are inaccurate because after each few cycles/readings the voltage fluctuates, bouncing between 340-400V. The duty cycle starts out around 70% when first turned on, then after running for a few minutes climbs and stays at 90%.

Lastly I tried replacing the 1KV caps (with these https://www.mouser.com/ProductDetail/81-RDER73A103K2K1H3B), and the BYV26E diodes (with these (https://www.mouser.com/ProductDetail/78-BYV26E). There was no improvement.

Can you see anything wrong with the specs of the new components I have installed? Is it possible that the inductor now has too low of a resistance (4.5)? I have checked my solder joints and they appear to be fine. I have 4 more PCBs that I can try a fresh build with– but I would like to figure out why this one isn’t stable.

Any advice you can provide would be great, thank you!