Hi everyone,

Three months ago I made my first SSTC with a single mosfet driver (IRFP460) and with manual tuning. I had nice result at 333kHz RF (without topload) with around 3 cm continues sparks and with the mosfet cold (40V input).

Now I pass to a half bridge driver with this circuit of Kaizer:
http://kaizerpowerelectronics.dk/tesla-coils/kaizer-sstc-i/

The only thing that I add, is another 555 timer for manual tuning (their is a jumper that allow me to choose manual or auto).
On the output of 74HC14, with the coil off I have a perfect 50Hz (of my main house I think). Switching ON the coil I have a very "nice" mix of 50Hz with RF and duty cycle of pulse.
I tried to put the driver one meter away from main AC or supplies but the same result... It disappear only if I switch OFF all mains in my room.

Now, I have 3 big questions, and hope someone can help me:
1. Is it normal to have less results with this half bridge driver, like 1cm spark and drawing about 400mA at 40V?
2. What can I do to remove that 50Hz? A hi pass filter on the input of 74HC14 will help?
3. A triac-diac module is a cheap solution to a variac (I found in amazon to control motors until 4000w)? It will work? Is a good solution to use this module before full bridge rectifier?
(the triac-diac: https://www.amazon.com/WINGONEER-Electronic-Regulator-Thermostat-Controller/dp/B01LXLU3SD/ref=sr_1_6?ie=UTF8&qid=1523648449&sr=8-6&keywords=voltage+regulator+ac)

I would like to connect my SSTC at the maximum power to 220VAC soon, but I will like to slowly smooth step up the input voltage (if I will solve the 50Hz problem).

Thanks in advance, and hope someone can help me,
Best regards