Put in the SS diodes, with some resistors or a choke to set the voltage. Use the 5V winding to buck down the primary. I think I saw a bad 5V4 or 6X5 yrs ago, but I've never seen a 5U4 or 5R4 short. They have quite a bit of space between fil and plate and I've used the 5R4 up to 800V. And how about a fuse in the secondary? Wilson W4BOH