Unknown RCA tube

Who knows this RCA tube? Type designation is not readable.
Some informations: height 2 6/8 in., diameter 1 1/8 in. It's a pentode system with B9A base.
Uf = 12.6 volts @ 0.26 amp. at pin 4 & 5, filament is center-tapped at pin 6

Pin 1: K
Pin 2: G1
Pin 3: G3
Pin 4: f
Pin 5: f
Pin 6: fm
Pin 7: A
Pin 8: G2
Pin 9: G3

Any hints are highly appreciated, thank you!

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The question has been solved in the German speaking forum, the unknown tube is named 12HG7. For me it's unusual that this type has been manufactured in 2 different shapes. The pictured tube is quite thick, but the common dimension (or diameter) is also represented. Do anyone knows the reason for this?

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