I have an EL34 headphone amp that sounds quite good. Among pentode/tetrode tubes, my favorites are very low powered tubes. I run 349 output tubes in pushpull that deliver about 4-5 glorious watts per channel. This is my favorites tube aside from the truly crazy rare 252 tube. My next favorite is the 350B (a variant of the 6L6 tube), followed by the 6L6 or KT66, and then EL84 (a tube often used in less expensive amps, but, I’ve never heard an EL84 amp I didn’t like).
Of triode tubes, either pushpull or single ended, I particularly like the 45 and 2a3.
