I had a sort of similar situation. I needed to regulate a high voltage
for a tube rig. The PS that I had delivered 325V and I needed 275. I put a zener
diode across the pass transistor to guarantee that the voltage across it wouldn't fry it during turn-on and turn-off. I also used a long series string of diodes to get the 325
down to 290 or so, so the pass transistor only had to drop 15V.
- Jerry, KF6VB
