12ax7 vs 5751

I can't answer for Frogman but I certainly think for the most part that a warm tube sounds warm where ever they are with a few exceptions. there is no doubt though, that certain tubes just don't work in all circuits. For me as a rule I tend to like 5751s in most situations. I did try 5751s in the output section of a Jolida CD player and it simply did not function. The sound was dreadful enough to make me think the tube had failed but it hadn't. The circuit for some reason was intolerant. Another exception was a highly modded ARC SP-6B which didn't change it's tone no matter what I put in it. It was brutally frustrating and a terrible combination with my speakers.
There are cases where the lower mu doesn't seem to work either. I have some real old unmodded vintage integrateds that used 12AX7s in the preamp section and frankly need the extra umph. A couple of them came loaded with Teles before tube rape was common. Curiuosly they respond quite well to current production in many instances where I have replaced the old tubes. The old tubes I then put into new amps and many sound fine go figure!

Mechans, you answered for me very nicely; actually.

***I certainly think for the most part that a warm tube sounds warm where ever they are with a few exceptions. there is no doubt though, that certain tubes just don't work in all circuits***

I completely agree, although I know some will disagree. I currently own one piece that uses 12ax7's, but own and use three that use 6dj8's. In all three pieces the Telefunken 6dj8 produces a full bodied, dimensional sound with a timbre closest to "neutral" as I define it; reminiscent of the classic Audio Research tonality. In one of the pieces, a modded Melos 222c occasionally used for it's line stage, the Teles' fullness and lack of zip or edge is too much of a good thing for this preamp which is inherently on the dark side. With this pre, West German Siemens 7308, which yields a brighter, less corpulent sound, with excellent high frequency extension is
much better. I hear similar tonality/timbre from my Tele 12ax7's in my
phono pre.

I should have said: "I hear similar tonality/timbre from my Tele 12ax7's in my phono pre as I do from the Tele 6dj8's in my linestage"

Man I cant wait to get some different tubes!!
I am still getting used to the sound of this Thor, but is is very good.
Does anyone have experience with Phillips Miniwatt 12at7 from Holland factory?
Another Thor owner suggested the Miniwatt/GE 5751 3 mica black plates combo.

Mc,
Buy all means get a pair. I really like them, i use them in my VT 5.5 pre-amp, i also like and use the Phillips Mini Watt 12ax7. Very smooth i like them, as usual YMMV......