What could this Telefunken be?

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jcr1234
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What could this Telefunken be?

Post by jcr1234 »

I got an old Telefunken tube. The markings are completely gone. The only thing I can make out, is a little bit of the Telefunken name, and there is the diamond on the bottom of the tube with the number "10" inside.

It looks just like a 12ax7. When I test it, using the settings for a 12ax7, it tests too high, at 3700/3800 Gm.

I looked it up, and that Gm rating puts is where a 12au6 would be.

Is there any way to tell what this is? Does the "10" inside the diamond mean anything?
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dotfret
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Post by dotfret »

Try cooling it in the fridge and watching it warm up - sometimes you can see rubbed off writing appear when condensation starts to form on the envelope.

The 10 in the diamond refers to the workstation it was made on = you have to be German to get info from that!

The Telefunken 12AU7 looks very like the 12AX7. At least you know it is a real Telefunken - the print always rubs off!
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paulschnettler
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Post by paulschnettler »

I'm with DotFret on the likely guess that it's a 12AU7. I've got a handful of those as well. Tektronix used telefunken 12AU7's in there tube o-scopes. They seem to be treasured by the audio amp types and are offered at pretty good prices on flea-bay. :D
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