but to protect the amp from melting solderings or even worse the transformer or damaging something that can cause a risk of electric shock... If I blow a solid state there's no problem... but not a tube treasure...
Well, that's the thing, when these amps are tested, they're tested I imagine for running for very long periods of time - probably days, if not weeks. The solders, transformers, and other electrical are designed for continuous use. The thing that degrades electrical components is heat, and the components in the DT50 are designed to withstand the heat the amp produces for an indefinite time period. What happens with electrical equipment is that it warms up to a certain temperature, and then basically stays at that steady-state temperature until turn it off. There may some fluctuation in temperature based on how loud you're playing the amp, but it's probably not all that much.
Basically what I'm saying is that I wouldn't worried about playing the amp too much. It was designed to be played through. As long as you do the common sense things like use the standby switch when turning it on, avoiding turning the amp on as soon as you bring it in from a cold environment, and other typical tube amp care things, I don't think it's something you should really be worried about.
Time is a train
Makes the future the past
Leaves you standing in the station
Your face pressed up against the glass