What are some ways to tell if you have a Telefunken ECC83?

[TNJ]

I bought 2 of these from a dealer out east, for a very good price. Too good, perhaps? I have the tubes in my possession, and havent tried them yet. I have a friend who said, if there isnt an etched diamond toward the bottom of the tube, it isnt a real Telefunken. Is that right, because if it is, I got ripped off.
What other identifying characteristics are there on these tubes?

Thanks,
S.
j

[Mark Kane]

The etched diamond is right on the bottom between the pins.

[TNJ]

Thanks Mark...
I guess I'm o.k., because I didnt look on the under side of the tube...it is there! Wow...great deal on these Tele's then!
S.
j