The regens I built as a youth were always just one triode [0-1-0 in the old
description code]. They were for the AM broadcast band. Fine with high
impedance earphones. You'd want at least an audio cathode follower to drive
today's low impedance phones. [0-1-1 description]

Too bad I burnt out so many UV99, UCX99, WD11, 01A, etc, tubes. One wasn't
too sharp at electronics at age 12 or 13, & probably a bit clumsy w/ the
fingers.