Hi again.
Because i'm no eletronics vet, I just built the original circuit with 2 diodes. And it worked perfeclty for about 30secs. Then it a strange popp sound "pop piuuu-plim, tr pöööööö" and then the element was all the way in and hummed. It sounded like that it had gone on overdrive or something. Then I powered it off and waited for a while and then I put on again. Same thing happened. I tried to put more diodes as you suggested, but the same happened again. Then I accidently tripped over the cables that went to the element, and they got lose and then it blue the fuses. I guess I destroyed the output transistors, didn't I?
SO, do you know what went wrong?
Thanks for your time!