tube amp on with speaker wire disconnected

Running a tube amp without a load can cause damage.

Regards,

Amp damage under those circumstances is a risk, but it is not a certainty. A brief disconnect at medium or lower volume is less likely to cause a problem than an extended open circuit with the amp cranked.

Susceptibility to damage is also dependant on the brand, model and condition of the amp.

If you've reconnected the wire and the amp now seems to play fine, I wouldn't worry about it.

Depends on the tube amp honestly.

I've had the speaker wires come loose and never had a problem. I also am biwired using two sets of cables and I have had one cable come loose that was connected to the bass woofer. I just reconnected it and it was fine. In fact, this is weird, but last week, I was playing my set and only one speaker was connected, as the cleaning lady accidentally knocked off the speaker wire connections to my right speaker. I was listening to music out of the one speaker for about 30 seconds before I realized one speaker wasn't on. I reconnected without a problem. I think it takes a lot more to damage a tube amp than a loose connection for a minute or so, at least in my experience. BTW, I have a conrad-johnson tube amp.