6F8G RCA gray ribbed staggered plates NOS no printing 1950 era (7ma/8ma)

6F8G RCA gray ribbed staggered plates NOS no printing 1950 era in white box

7ma Gm=2500

8ma Gm=2600

Good Ma range 7-9ma

Good Gm range 2400-2600

NOTES: 

GE, Sylvania and Raytheon have mirror image parallel black plates

RCA and Ken Rad have staggered black ribbed plates

6F8G dual triode = (2) 6J5G's triodes in 1 tube