[quote name='Mr. Foxen' timestamp='1363872237' post='2018680']
That page seems to miss an important bit about the different impedance of the different valves having an effect on the circuit, which shifts tone around in various possible watys depending on what the valve does, the two halves might do different things.
[/quote]
That's true Oli, but they do say this:
Before you discover the new possibilities in your amp, let us give a [b]disclaimer[/b]. Your amp was originally designed for a certain type, and although tube amps are often forgiving, it may not have a tone that you like with a different tube type. For instance, changing the tube type doesn't only change the gain factor; there are other variables as well and your amp may have a circuit that is more particular than others. As a general rule, the substitutions we describe here should work well but there are exceptions and [b]we don't warranty[/b] any problems that result from trying mismatched tube types.