Here is the final impression of testing the GE 6CG7/6FQ7 tube after burning it in for close to 40 hours. Basically it accords with what I wrote before:
Compared to it's Japanese Raytheon cousin it is darker sounding and not as quick, but the bass is fuller and more hefty, but could sound boomy. The mid range is good with a lot of detail. Timbre excellent and no sibilance in the treble. Sound stage is impressive. Both the bass and treble are more recessed in the background compared to the Raytheon that is more forward and open sounding.
This tube is quite good and reminds me of an upgraded Ei 6HM5 "fireworks" tube in how it sounds. There are two peculiar u-shaped attachments on top of the top mica. (I have three other GE 6CG7 tubes that don't have those attachments - we'll see how they sound at a later time.)
Conclusion: A nice tube (and far superior to ANY 6AK5 tube) but does not get top honors.
Next: A RCA 6CG7/6CQ7 side getter tube from July 1972 (Code DX). Judging from the somewhat bent pins it probably is a used pullout. Used is sometimes better - does not require grueling burn-in.
First impression: It sounds different and lower gain. Let's leave it at that for now until my listening brain is adjusted.
The blotch on the left inside the tube is the side getter flash.