Telefunken Tube Information Sources?


Can those who are deep into vacuum tubes direct me to the best (The best Jerry, the best) sources of information on small signal Telefunken tubes, particularly the 12AX7 and 12AT7? I see them priced from reasonable to VERY expensive, and I don't even know the desirability of the ribbed vs. smooth plate versions. I gotta finally educate myself!
128x128bdp24
Great, thanks. I've seen Brent's name mentioned often as one of the couple of best sellers of vintage and rare tubes, glad he also provides knowledgeable info on them.
Here's a great link that covers all signal tubes. It's been around for quite awhile but has great info on tubes. I've used it for years and got alot of info. Its Joe's Tube Lore.
https://www.audioasylum.com/scripts/d.pl?audio/faq/joes-tubes.html
Alo do a search on the Asylum Tube section for posts from Bambi B. A lot of great firsthand use info on the 12AT7 variants.
@bdp24  Joe's tube lore is a good reference, but I would not call it accurate regarding 12AX7s. He makes no pretense saying he doesn't like this tube type. 

Brent Jessee has a better description of sonics on different brands and tube types.

One characteristic of Telefunken is they are extremely linear. So, no sweet mids, but great dynamics and open sonics.
 And it's true that Siemens rival Tely's.