Hi! Just a little question: ...how does a tube amp affect a pedal sound?
I mean: why my Boss SD-1 sounds better into a Blackheart tube head than into a Fender Frontman 65R transistor amp, using clean channel on both amplifiers?
Also, will a Boss GT-10 sound better into a tube amp than into a transistor amp, obviously with the preamp/cab simulation disabled?
Thank you!
Tubes handle overloads much, much better than transistors. Overdrives especially sound better on tube amps for that reason. Tubes will clip very nicely - that is, gradually and smoothly - when presented with an overload. Transistors clip violently and abruptly.

As far as the boss unit, it will probably sound better with the tube amp simply by virtue of it being a better amp. With things like delay and reverb it won't make much difference, with overdrive or distortion models, again, you'll see better response from the tube amp.