Help with identifying tube

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I have an old Telefunken tube here that I don't know what to do with...
It looks like a dual triode to me, and there is some kind of shielding in the middle, connected to pin 9.
The markings are all worn off except the number "387" printed on the top. Also, the number "29" is stamped inside the diamond on the bottom and "16" penciled on one of the plates (visible on the picture).
Heater seems to be pin 4 & 5 (about 2.8 ohms between them).
I've put it next to a Telefunken ECC82 for comparison, the "mystery tube" is on the left.

Picture will hopefully be up in a little while.

Any ideas? 😕

 

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I think I've solved it - I'm pretty sure it's an ECC85. Same pinout as ECC88, only higher mu, so maybe I can try it in a phonostage just for fun...