Not smaller, but more along the lines of classic
(glass, pin sockets)
tubes. Motorola WWII walkie-talkies used "pencil tubes". I've only seen
them once, about the size of a small woman's pinkie finger.
Actually, SCR-536 (and friends) use minis, not subminis. You may be
thinking of the 1950s AN/PRC-6, the sucessor to the SCR-536. They indeed
used subminis.
William Donzelli
aw288 at
osfn.org