I have a Powerblock, Fender Pro Jr and Epi Valve Jr. If you crank a 5 watt amp, there is plenty there to get noise complaints.
But I think using anything more than 15 watts means you have to turn it so low that you neuter the sound, so I would use that as a max for tube amps. SS is more forgiving, so the 150W Powerblock works fine.
Also, Weber makes smaller attenuators, in 15 and 25W varieties. I have a 25W attenutator that I can use with the two tube amps to trim the volume a bit. I'm not sure how much "better" it works over just turning the volume down, but it does include a line out, so you could set the attenuator to max, so there was zero sound output, and run that into a recorder, in order to have real tube tones on your apartment recordings. In this way, you could completely crank the Pro Jr with no sound to bother neighbors.
