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Which tubes are the best?

Hi folks, I just got a Muzishare X7 integrated amp. It is beautifully made and sounds like it has a lot of promise. Even though I'm just breaking it in, I am thinking about tube changes. Why? It's just what I do. 
I'd like your opinion on the best replacement tubes, meaning smoothest, most "tubby" and mellow tubes. 
I won't be chasing NOS tubes. I'd like your experience with Gelenlex Gold Lion, TungSol, Mullard, Telefunken, or?,  etc. of current manufacture. The amp uses KT88, 12ax7, 12au7 and CR34 rectifier. 
Any thoughts about KT88 vs 6550 would be appreciated. I used to prefer 6550 way back when. 
Any information would be appreciated. Yes, I could go through all the old posts but I do have vision issues after four operations and that's why I'm asking straight out. 
Thanks in Advance. 
Back in the day, I used to do some serious tube rolling. The absolute mellowest, most laid back and detail rich tubes I ever found were some Mullards advertised in the back of Audio magazine. They had Magnus Organ printed on them. They were amazing. Unequalled. Ten years ago, I was cleaning out stuff and took a box of my small tubes to a local dealer. Some guy gave me $350 for them. Wish I still had them heh. 

fredcdobbs
jjss49's avatar
jjss49
6,612 posts
 
as i understand it this muzishare unit is basically a primaluna knockoff with a tube rectifier and downgraded output transformers

so i will share my thoughts on tubey tubes

old stock ge 12au7/ax7

tungsol (new russian) 7581’s if like the primaluna’s this unit can autobias and run 6l6gc/kt66 equivalents - in general i find current russian power tubes less sharp and treble intensive than the chinese counterparts
roberjerman
4,319 posts
 
You can't go wrong with any of the Slovakian-made JJ's! I'd replace the Chinese tubes presently in your amp with all JJ's! 
millercarbon's avatar
millercarbon
12,531 posts
 
I've run tube integrateds using 6550 or KT88 for well over 25 years. Yes there are differences between tubes but nowhere near enough to me to be worth changing (rolling) just for the sake of change. Tried it, no thanks, bigger fish to fry.

That said, KT88 are a bit warmer, with a bit more tubey liquid magic than 6550. Enough so the warmest 6550 is still not as nice as the most flat least warm KT88. There's just not enough there for me to be chasing after expensive NOS, so you are welcome to go fishing and good luck landing the big one. But of all the tubes over the years my favorite by far is JJ. Better more 3D liquid than most if not all, and yet still with great extension and control, but what clinches JJ for me is their reliability and longevity. So +1 roberjerman, JJ all the way!
atmasphere's avatar
atmasphere
12,164 posts
 
JJ KT-88s are quite nice and hold up well too. They make some upscale versions like the 'blue glass' that seem to be worth the slight extra dollars. The Chinese make a very nice 12AU7. I avoid 12AX7s in my designs so I can't comment about that one. But we've had a lot of nice feedback on the Psvane tubes, and also some nice comments on the Gold Lion (Russian made) 12AU7, so those might be good places to look for a 12AX7 that isn't NOS.
facten
2,971 posts
 
With my Ayon Spirit 2 I prefer the sound Gold Lions or Psvane KT88s to either the clear or blue bottle JJs , but you need to try tubes for yourself to see what sound flavor you like.That amp takes 4 12Au7s , I use two NOS RCA 12Au7s blackplates, and 2 RFT ECC82s.

I have 2 other integrated amps that use 12X7s, in my Line Magnetic I use NOS Tungsol 5751s to reduce the gain a little; in my Finale Audio I use NOS GE 12ax7s

To my ears changing out the respective JJ , Electronic Harmonix or Chinese signal tubes that came with each amp took the sound to another level; worth the expense
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