What is your impression of vintage Telefunken signal tubes ?

@inna Re the ECC83/12AX7: Add in great sound-staging, imaging, fine detail retrieval, superb dynamics, an absence of grain or harshness and most importantly, flat frequency response. Ribbed plates are a little brighter while the smooth plates have a slightly smoother top end. 

Everyone likes clear and transparent sound but there are other elements of realism that are no less important.

Installed a pair of Siemens 12AU7WA in my preamp about 5 hours ago. And they sound liquid, 3D with a humongous wide sound stage. No experience with Telefunken - but have always read great reviews. I think a lot depends on system matching too?

noromance, I see.

I have a VAC Avatar SE integrated, it uses three 12AU7 in the driver stage. When I asked Kevin, the designer, he recommended Brimar and Sylvania, and that's what I put in it - Sylvania long black plates from 1950s.

I thought I might try at some point Telefunken/Siemens/Valvo.

I use 12AX7 Mullard long narrow plates from late 1950s for phono and line amps, and Mullard EL34 XF2 power tubes.

Everything sounds excellent, very balanced. No need to change anything, just audiophile curiosity.

I roll 3 different NOS tube sets in my pre: tele medicals, brimar cv4003’s & Siemens nickel plates. I like all 3, but my go to are the Tele’s. Smooth, linear, clear & accurate. 

My Telefunken ECC801S do the full range well.  The clarity and detail is what sets them apart from other tubes that I have.  If they were poor in the mid and low frequencies, I wouldn't sacrifice those. 

The Siemans ECC801S are close.  Looking at ebay, a nice matched pair is getting pricey and difficult to find.