Thanks Soundhound. What are your thoughts on zero auto transformers from Paul Speltz? From what I have read they seem to make a big difference. I can pick a used pair up for $300, should I do it?[/QUOTE]

I am not familiar with these transformers, however I would stay away from autotransformers (if they are indeed autotransformers) - SET amps sound fine already. The traditional transformer used in a SET amplifier is actually not something that needs "fixing" as long as it is of high quality. Any SET amp of good quality will sound great in stock form, or with some subtle mods. I have replaced the coupling capacitor between the plate of the driver tube and the grid of the output tube with a NOS oil capacitor which made a difference for the better. I also constructed a regulated DC power supply for the filament of the 300B output tube for noise reduction reasons since my horns are 106db/watt efficient and need a squeaky clean noise floor.

If you get the urge to tweak, I would stick with maybe a higher quality traditional output transformer, maybe oil coupling capacitors, and if your amp uses a 300B output tube, Svetlana makes a very fine one.

These amps sound just stunning as-is.