Actually, where I’m from, we call ’em valves.
I was getting a lot of noise (that is, unwanted noise) from my guitar amp, so on Nichol’s advice, I retubed it. How convenient that Encore had some Electro-Harmonix valves in stock (though I’m told that The Tube Store turns around orders quickly and cheaply). The Champion 600 only takes two tubes, a 12AX7 and a 6V6. They’re a bit like changing a fiddly lightbulb; the hardest parts were working out how to open the 6V6’s retainer (push down on the wings), how to open the 12AX7’s shield (push and twist – it’s a bayonet a bit like UK light bulbs), and how to seat the 12AX7 when the holder obscures most of the pins (the gap faces the middle of the amp on mine).
Result? Nice. Less noise (though a Tele’s bridge pickup at full volume into a valve amp won’t ever be clean). More fun. $25 well spent. Strange to think that I’m installing components which were getting a bit old hat when my dad first started in electronics.