Base codes can be very misleading. The etching on glass can be helpful I’ve found.

I want those! Beautiful. Thank you for sharing. Do they sound any better than the two in your first photo?

I agree. I bought the three GTAs for a pair of AtmaSphere M60’s, they run one of the 6SN7’s at Those bottom two tubes are from the 40’s. They are GT’s. I bought the three GTAs for a pair of AtmaSphere M60 amps. They run one of the 6SN7’s harder than GTs can handle. I agree, lovely tubes:)

AWV Radiotron The pair with the support rods are very special.

maybe a 40’s era RCA 5u4g with a brown base? That tube looks identical to to my RCA 5u4g.

Later versions of the RCA only have one getter. But they are usually a rectangular getter, that dimple foil getter is what is throwing me off.

You could try Westinghouse GTB’s, they are found fairly cheap and sound very good. Raytheon GTB sound decent too and again reasonably priced. I’ve also had good luck buying Australian made tubes from Australian fleabay sellers. Great sounding tubes again at real world prices.

Looks like an RCA 5R4GY to me

My guess is the three Russian made tubes probably have identical construction, so save your money on labeling, it probably won’t make a difference.

It looks to me like the tube in the middle with the black glass is a TungSol tube. Nice sounding tubes.

I agree with you, those older AWV 6SN7’s are fantastic. Some of the quietest tubes I own in the 6SN7 family.

I think so. I go by the internal structures. Look for a 5u4g with the two supporting rods between the plates.

Which RCA are you running? The older ones typically sound a little better.

Believe it or not I have one black glass NU 6SN7 that has the same round plate structure as the 6F8G. I’m sure they are uncommon but they do exist.