Tubes are fun, rolling them can turn into an obsession. Great advice already, if you can, identify the sound signature you are after. It can vary depending on design. Some designs lean into tube magic, bloom. Other designs focus on bridging the gap between SS and Tube amplification often leading to Tube amps that sound more like SS amps with a touch of Tube magic. If you are new to tubes if you can find a unit with auto bias / bad tub indicators it will ease you into the maintenance of keeping Tube amps running, sounding there best a bit easier.