Hello Stefan,

You wrote: > Just like Tesla transformers are fed with a primary winding of 
some turns, something between 5 and 20 probably. 

Take a look on my web site for pictures of my 3 KVA Tesla coil which shows the 
primary-secondary coupling:

http://www.hurontel.on.ca/~weazle

Fine tuning is required to get the maximum streamer length and a tap move of 
only a few inches can make a HUGE difference.
On my LowFER beacon I couple the final to the bottom of my loading 
coil/variometer with three turns wound to sit in the
"valley" that is between the loading coil's winding of #12 THHN wire.  I'm sure 
it would work at higher power.

73, J.B., VE3EAR

LowFER Beacon "EAR"
188.830 kHz. QRSS30
EN93dr