Experience with FREDs in a tube amp PS

IME in a high-voltage custom full-wave bridge, Cree SiC Schottky surpasses HEXFRED. For low-voltage/high-current filament supply, a ladder of 50V Schottkys sounds better than FRED. In a manufactured 4-pin bridge, IXYS 600V/6.6A SiC Schottky is reportedly good, although expensive.

You will hear across-the-board improvements, but particularly improved dynamics and faster bass.

To be safe you might try 1200V/10A Cree SiC Schottkys, but depending on power drawn, they might still need heat sinks. Lower voltage/current diodes may be OK if the amp is equipped with a soft-start thermistor on AC. Dennis Had might offer an opinion.

Generally speaking, the safe thing to do is to select replacement diodes that equal or exceed the rated capacity of the stock bridge. Chances are good that this can be done without using heat sinks, unless the original rectifier uses them.

It's definately worth using Schottkys if you can figure it out-- both for B+ and for the low voltage filament supplies.