Yes, many small SMD parts monitor the operation of the amp and will mute it or shut it off if a tube fails, any two points are shorted, or the speaker wires are shorted. This protects the amp and the tubes in case of failure. The small tube LEDs will trigger the red indication for either channel depending on the problem.
The actual amplifier circuitry is modified for higher performance, greater bandwidth, higher signal to noise and meeting specs when the tube performance drops off, especially in the driver stages. To accomplish this operational voltages have been changed as well as the output transformers for more bandwidth.
Thanks,
Ron-C