'Fast' often refers to risetime or slew rate. Spectrals have always been very 'fast' in this regard. 100V/microsecond is generally considered 'fast'.
Most tube amps are 'slow' by comparison- 15V/microsecond being typical. Our amps are 600V/microsecond- IOW they have speeds similar to the best solid state. Tubes are not inherently slow (after all, if they were, color television would not have been possible...). But there can be design elements that can slow any circuit down.
'Fast' and 'slow' should not be confused with 'bright' and 'dull'; these are entirely different things, even if an amp that is 'fast' is also 'bright'. There are different reasons for these things!
Most tube amps are 'slow' by comparison- 15V/microsecond being typical. Our amps are 600V/microsecond- IOW they have speeds similar to the best solid state. Tubes are not inherently slow (after all, if they were, color television would not have been possible...). But there can be design elements that can slow any circuit down.
'Fast' and 'slow' should not be confused with 'bright' and 'dull'; these are entirely different things, even if an amp that is 'fast' is also 'bright'. There are different reasons for these things!