Best mellow sounding 12ax7 for Thor TA-1000 preamp

NOS Telefunken ECC 83s
and if you really want to break the bank ECC 803 s

Andy at Vintage Tube Services is without a doubt an incredible source, impecebly knowledgeable, the most refined  testing, my highest recommendation.

Thanks for all the great advice guys! I tried two NOS Mullards and it helped quite a bit. Then I changed by DAC caps from Dueland back to Audio Note coppers and that helped even more. A cable change or two and I should be good.

Hi, i just happened to stumble across this thread. I recently aquired a Thor TA-1000 mkii preamp. (at least i think it's a Mkii) The serial number is greater than 1000, and I read that if that's the case then it's a mkii?? Is there anywhere i can get an owners manual for it, and  If not does anyone here have one that they could make a copy for me? I would be willing to pay for your time and of course the mailing cost. One of the questions I have is what is the toggle switch on the back for? it isn't labeled. thanks for any help! 

Probably not very useful but my mark I serial number is in the 200's. I dont know when the mkII started.

The only switches I could imagine would be either a USB/rca input switch (does it have a USB input?) or a phone mm/mc switch, if the preamp is a ta-2000 with phono.

I have an owners manual I can scan and email to you if you still need it. 

My TPA-1000 Mark II serial number is 231