Great! Thanks for the super quick advice! Haven't got a valve amp yet. Just planning ahead. But good to know whats what.
What speakers?
Sonus Faber Concerto Home.
I'd agree in theory, but my Leak Stereo 20 seems surprisingly happy driving my JR149s (84 db or so, but an easy load), though I do listen in the extreme near-field and not very loud. To be honest I'm amazed sls4321 found 4 KT88s a side struggled with Harbeths, I drove both Compact 7s and SHL5s with a Prima Luna Prologue 2 stuffed with EL34s (30-35 Watts) and never felt it was struggling at all, though again I'm not a high volume listener (and neither are Harbeths high-volume speakers). I'm also the type of listener who hates small speakers driven loud by anything, I'm a firm believer that if you want loud you neeed big speakers as they just move more air with less effort. I'd have thought a good quality 30-40 watt push-pull tube amp would take a pair of 86db stand mounts louder than I'd want to be in the same room as them assuming no really nasty reactive loads or impedance dips. Sonus Fabre seem to often be partnered with tubes so I suspect all will be well.
Sonus Faber Concerto Home.
Something like that.There's also something about safe operation parameters too isn't there? I'm still very much grappling with the very basic stages of electronics, but as I understand it the output transformer is kind of a safe conduit/translation device that enables the output tubes to communicate with the speakers. Something about converting high voltage and low current into lower voltage and higher current or the other way round or something like that, but if the impedance mismatch on the outside (speakers) is too great the tubes the other side of the output transformer end up being forced to operate outside their design parameters and can overheat, wear too fast or otherwise fail. I'm kind of regurgitating this from decades ago with regards to hooking too many cabs up to a tube bass or guitar top, and in that context you also need to know about series or parallel wiring etc as it all impacts the impedance.