I agree about lack of interest, can't understand why, except it was all very popular for quite a long time. Perhaps people just moved on to other types of experiment.
That conical coil sorveltaja is very cool. Big thumbs up from me, because I know how hard it can be to wind a conical tower !
Best method i've found, is to poke two small holes near the top of the coil form, through which the start of the winding goes. Then, run down and around and every now and again put a couple of drops of white glue on the windings to make sure they don't move. Would be good to know how you did yours
The 2SC2655 is quite good on the amperage handling I see, 2A, with 0.5A to the Base. Your pair may perhaps be further enhanced with 2 diodes to the Base.
I've got a 5V circuit here, that was showing signs of heating the transistor (note for Nick too maybe) - 2x N45HER203 (medium sized black) diodes forward biased toward the Base, both increased power output several fold and allowed the transistor to be just hand warm after an hour of running. 1 diode helped, but not much, adding another made the world of difference. 3 and the drop was too much, the transistor stopped !
Transistor in this case is a D2641, Slayer circuit without a resistor...I start it by using a piezo lighter at the side of the tower.