(!!) (#1 37 Pair) 37 RCA NOS 1940”s (8.5ma and 8.5ma) 1% matched

1 matched pair) 37 RCA NOS 1940”s same build

1 tube) 8.5ma Gm=1100

1 tube) 8.5ma Gm=1100 RCA made for Marconi Canada

Test parameters:

Vplate=250V

Vgrid=-18V

Good Iplate Ma range = 6.5-8ma

Good Gm=1000-1100

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