This is a theoretical question, although I just might try it.... Are there any fixed bias single-eded amps out there? I am looking at putting a 5F11 PT into my 5F1. It is a bolt-in upgrade to get a bit more punch into the 5881 tube I am using. It has a tap for fixed bias. The advantage would be the ability to dial in optimum bias for 6V6, or 6L6 or 5881 with the twist of a trim pot. What are the tonal differences between cathode bias and fixed bias, particularly when used with a single-ended amp?