Quite a discussion going on here while I was away from the computer, I like that😀
As I could use some extra 450V caps and more wire, I've decided to place an order including some 1300V PIV diodes. The mains voltage where I live is remarkably stable at 230-235V but as I mentioned before, a collapsed negative rail has the potential to take a lot of parts down with it. Russian triodes and Lundahl/Hammond transformers are perhaps not the most exotic and expensive parts around but still worth protecting from disastrous events.
As I could use some extra 450V caps and more wire, I've decided to place an order including some 1300V PIV diodes. The mains voltage where I live is remarkably stable at 230-235V but as I mentioned before, a collapsed negative rail has the potential to take a lot of parts down with it. Russian triodes and Lundahl/Hammond transformers are perhaps not the most exotic and expensive parts around but still worth protecting from disastrous events.
I use at least uF5408 diodes no matter what. There are some nice FRED diodes at Partsconnexion that are 1200v at 6amps in a TO220 package. They are a lot more expensive but at least you’ll have peace of mind. It’s worth remembering that not spending a few extra dollars can destroy a whole amp!
An additional item to keep in mind when derating is to include current derating as a factor in addition to voltage derating. This is because the higher the current is, the hotter the diode which can aggravate voltage stress, and therefore the lower the voltage margin. In the case of the SPP board, I would not worry about using UF4007 since the voltage derating is 77% with about a 20% current de-rating. No major temp rise so the 77% (below 80%) is sufficient.