Both of the comments above are spot on. I was actually at a dealer looking for an OTL amp to get the kind of immediacy and vibrancy that my pushpull triode amps do not quite deliver. I found that a SET can actually deliver that kind of immediacy without the slightly rough and crude sound of some OTLs. I ended up with an OTL that uses parallel 2a3s. The 8 watts they deliver are enough for the 99 db/w speakers that these amps have to drive.
TWL is absolutely correct about transformers. My SET amp is made by Audionote. I've heard various models of their amps, and the ones with better core material and silver wire in the primary and secondary windings sound much better than models with lesser trannies. I know it is a matter of preference, but I also prefer triodes other than the 300B, which, to my taste, sound a bit bloated in the midbass. I personally like 45s; 2a3s can be a bit lean and analytical sounding, 45s sound like they fall between the 300B and 2a3s.
TWL is absolutely correct about transformers. My SET amp is made by Audionote. I've heard various models of their amps, and the ones with better core material and silver wire in the primary and secondary windings sound much better than models with lesser trannies. I know it is a matter of preference, but I also prefer triodes other than the 300B, which, to my taste, sound a bit bloated in the midbass. I personally like 45s; 2a3s can be a bit lean and analytical sounding, 45s sound like they fall between the 300B and 2a3s.