I looked up some info. on the Novachord and octal-based tubes.  The
Novachord, being produced from 1939 to 1942, was well within the octal
tube era (octal tubes started being made in June, 1935).  A lot of the
tubes in this instrument were type 6W7-G, which is an octal-based tube
with pin No. 6 omitted (presumably because it has a grid cap), rather
than a seven-pin base.  Also possible is that emergency wartime repair
forced substitution of some of the 6W7-Gs with a seven-pin tube such as
the 6D7 or 6E7.  This required replacement of tube sockets, which was a
lot of work, but it was often done to keep 'em going.

Dave Vincent

 [ For those who are unfamiliar with "octal base" tubes, these are
 [ radio tubes about 1.125 inches in diameter with an bakelite
 [ 8-pin plug soldered onto the bottom of the tube.  The octal plug
 [ has a keyed protrusion in the center about 0.25 inches in diameter
 [ so that the tube gets plugged in correctly.  The pins are equally
 [ spaced in a circle and are all the same diameter.  --Jody