(!) (Pair) 37 Tungsol engraved base 1930's used/test strong (6.8ma and 7.6ma)

1 pair) 37 Tungsol engraved base 1930's used/test strong

1 tube) 6.8ma Gm=900

1 tube) 7.6ma Gm=1000

Test parameters:

Vplate=250V

Vgrid=-18V

Iplate good range 6.5-8ma

Gm=1000-1100

(Filament=6.3V @ 300ma, many think the 37 sounds better than the 76)