I used this core:
https://www.jaycar.com.au/l15-35x21x13mm-toroid-or-ring-cores-pk-2/p/LO1238

As planned I carried out some tests, and I think I made some progress.

Image 1   I slowed down the 555 to around 300 Hz
Image 2   Connected 350 kHz signal to the antenna
Image 3   Schmitt output at 350 kHz - looks a bit messy
Image 4  UCCxxx22 output - also messy
Image 5  UCCxxx21 output - messy, but a LOT cleaner than before
Image 6  Both UCC's together ( xxx22 CH1, xxx21 CH2 ) apart from that weird waveform, I am really pleased to see that now I can see inverted signal on UCC xxx21

Next job is to figure out the reason for that bad signal form on the  UCC's.
I disconnected the 555 and fed exactly the same signal from a generator, UCC output did not improve.

Hi Mads,

Thanks for your comment, what would be an ideal frequency for the 555 ?
I noticed that 555 is connected to the enable pin of the UCC’s and it did cross my mind that it will switch them on and off at a given frequency but I could not understand why ( I mentioned that im OK with electronics, there is lot to learn )
From your comment I gather that is to allow the transistors to “take a break” so they do not overheat.
Thinking along those lines, there must be a frequency that is optimal for that job ?

Hello everybody,

First I would like to mention that I am aware that I am starting a new thread straight after a thread based on the same design, which could be considered as Double Posting. So I leave it up to the admin to allow it or not.

Anyway, after successfully building a SRSG Coil a few years ago, I decided to have a go at building a SSTC because it will allow me to experiment without a noisy spark gap, also everything is smaller and easier to handle.

For my first attempt I chose Steve Ward's Mini SSTC Design, it looks simple enough and easy to understand.
My understanding of electronics is OK, should be sufficient to build this circuit, but please forgive me if I ask a "dumb" question ( I'm only dumb till I get an answer  )
Anyway, I built the circuit and powered up the low voltage side to see if anything will go pop, aaand to my delight, there was no pops !
I recently got myself a new digital scope to replace a very basic CRO which is at least 25 years old, so this is a perfect opportunity to put it to a good use so I had a poke around to see how things are buzzing.
There are a few things that I do not make sense, perhaps of my lack of understanding, perhaps there is a fault somewhere, so I decided not to give it a full test until I get some clarification.
I hope somebody will be able to help me out with this. I used this fantastic feature on my new scope to capture a few screen shots ( what a great feature !!! )

Image 1 shows output of the 555 timer, looks ok, but it gets bit wonky at higher frequency
Image 2 shows UCC37322 output, so far so good
Image 3 shows UCC37321 output - that looks weird, tried another ic, same result. I would like your opinion on this one
Image 4 shows input signal on Schmitt trigger - from my ancient function generator
Image 5 shows output signal from the Schmitt - it is Schmitting quite nicely I think
Image 6 shows output from the UCC37322 with Schmitt only connected 555 has been disconected
Image 7 shows output from the UCC37321 with Schmitt only connected 555 has been disconected - Why is this not inverted signal ? I was
               expecting it to be...
Image 8 shows output on the UCC37321 / 22 with the 555 and Schmitt connected - What a mess... What is going on here ??

GDT is built and it works quite well, I tested it as per the instructions on another page ( with a function generator and a scope ).
I dare not plugging this thing in, because I reckon something will burn unless I clear this up.
Any help will be appreciated.