Bifwynne, No input signal is OK. Tube amps need load, SS amps don't.
SS amp might fail when input signal is present and output shorted (overcurrent). I've heard that some poorly designed class D amps might go into oscillation without load but likely will survive that.
Tube amp might fail when input is present and output is open (overvoltage). It might even happen without input signal if amp goes into oscillation.
I increase volume slowly, at first, making sure I hear the sound from both channels. It is good habit, IMHO, since things tend to get shorted or disconnected between listening sessions.