Regarding protection of tube circuits and tubes, PrimaLuna integrated amps come with "bad tube indicator" circuits: when a power tube starts to fail, the BTI puts the amp in safe mode and a red LED lets you know which tube is the culprit. I think it's a great feature - it has saved my bacon a few times in the 8 years or so I've owned my PrimaLuna.
Tube amplifiers - software recalibration?
Do tube amplifiers need calibration adjustments periodically? Absent being properly calibrated can this cause amps to be shut down due to existing voltage monitoring controls designed to protect the tubes?
What types of controls exist to protect tube circuitry and tubes? I've heard McIntosh has power guard features, but I thought this extended to protect the speakers. Is this a good thing or does it impairs sonic quality?