Interesting observations on the Telefunken's, Harry, especially the part about more detail/louder volume in the high frequencies yet perhaps less dynamic overall. Sounds like bass is prominent also, especially if you can feel it (a positive as far as I'm concerned). Can't help but wonder what would happen if you combined the Telefunken with the Brimar....would it be too much or the best of both worlds? At any rate, thanks for the info and please continue to keep us updated on your tube rolling adventures, it is very interesting.
As soon as I can get to it, I plan to pull a Mullard CV4003 out of my old EAR preamp and try it with the RT........
Continued with the testing. I did combine Brimar with the Telefunken, and it did give best of both. It gave louder low of the Brimar. It gave more push and detail of the Telefunken. I just missed the blacknes and quietnes in the sound. It was more hifi than high-end, if you understand what i mean. At silenced parts of music, it was not black, doh there was no sound to be heard. At guitar music the Telefunken is magic. Adding the DC ring on the Telefunken spoiled the tube, and sounded not natural.
Then I ordered a second Telefunken, so I could try with only Telefunken. This gave a far better result. The sound is just as natural as with the original RT tubes. There is more push in the low, more detail and high. In general the result is brighter as with the RT tubes. It is still high-end, with now blacknes at silenced parts of music. also the 3d image of the sound is good. Specialli guitar music is magic with Telefunken. Again, using DC rings on Telefunken is spoiling the sound. The DC rings are damping the low, and giving less punch on percussion. In my case, the push in low is close to the limit I like. Placing my speakers further away from the back wall might help. According to my wife, this is no option
The Telefunken gives at least one step of volume more. Also I noticed more difference in the recorded volume levels. I had to adjust my volume to keep the played volume constant.
So my conclusion is that a set of Telefunken tubes is as good as the original RT tubes. This with more push in low, and a brighter overall sound. The 3d image is a bit less as the very well defined 3d image of the RT tubes.
I also tested two Harmomix tubes as a set. Then in the low, the sound is a bit messy. As result, the 3d image of the sound is gone.
I might look for some Mullard tubes, to try them also.
Harry