Kevin, in fact this was my first blown transistor over the three month period that I have been testing varioys SSG. I have built two SSG setups, one with a bike wheel and another with all parts made custom. Also I have built Ricks fan mod so that a big computer fan runs on a SSG circuit, charging batteries In all this time I did not blow any transistor, till now
Also I considered why the transistors blew. I figured out that this might have happen because of my variac, because when I experimented with joecells a year ago, the tube conditioning process involved using a simply rewired power supply like this:

I could do this without a problem with other power supplies but never with my variac, there was always a spark. One electronic guy told me that the variac is wired a bit different and can't be used like this. Therefor I probably acted harshly by saying that you can not add a ground/diode cable if you are powering your SSG with a powesupply, in fact you can, but do not use a variac like I did