Hey, Im pretty new to tube amps, even though i have owned one for over a year. I was looking through eurotubes trying to understand what a fixed bias really is, and came across this:

""Saying that an amp is fixed biased only means that the manufacturer used a simple resistor in the final bias stage instead of a variable resistor which is commonly referred to as a trim pot. So, if your amp is "Fixed Biased" and you want the best performance you can and should have the simple resistor replaced with a trim pot in series with a lower value resistor.""

Would that be a way of being able to put a different valve than EL84s into it?

Or would it still be El84s with an adjustable bias.