1 matched pair) 6C4C=6B4G Russian NOS 1955 and 1968 in white boxes - same internal build - bases are tight to glass

1 tube) 91ma Gm=6500 (1955) larger getter flashing - rattle inside base - dried glue

1 tube) 96ma Gm=6400 (1968)  - small rattle inside base

Internal construction superior to American made 6B4G

Test Data:

Vplate=225V

Vgrid=-30V

GOOD NOS Ma range 70-90ma

GOOD NOS Gm = 5200

Recommended for

(6B4G=6.3V filament)
(6B4G is electrically equivalent to 6A3, but 6A3 has UX-4 pin base and 6B4G has 8 pin octal base)
(The best sounding 6B4G are 1940's-1950's: Ken Rad, Tungsol, Sylvania, Raytheon)