Metal tubes were the first octal based tubes (1935). The GT came later.

Tube Lore, by Ludwell Sibley (http://www.eht.com/oldradio/tubelore/) is a
must have if you want to go deeper into the history of tubes.

The 6SN7 was always a GT.

Steve.
--
Steven D. Swift, , http://www.novatech-instr.com
NOVATECH INSTRUMENTS, INC. P.O. Box 55997
206.301.8986, fax 206.363.4367 Seattle, Washington 98155 USA