6GH8 substitutes

[kvflyer]

Side note, RCA manufactured the 6GH8 and used many in their color sets. They worked them hard and found that they failed often. In later production, they sourced the 6GH8 from Sylvania and of course, they were labeled as "RCA". You can tell which ones are manufactured by Sylvania easily. The tube number is obviously the ink and font used by Sylvania as opposed to the octagonal number surround.

I have tubes manufactured by both companies.