My first tube roll in a Primaluna Dialogue HP Integrated

First off, special thanks to tomy6--a fellow audiogoner who helped me identify, with specificity, the exact tube I was swapping in:  an Amperex 12AU7 tube made in the early to mid 70s; Great Britain Mullard factory. 

I swapped out stock Chinese sourced Primaluna 12AU7s--6 of them--from the preamp section. 

The process of rolling and twisting in a gentle swaying motion is really easy, yet there's an subtle art to it.  By the time I hit my 3rd or 4th tube, I got the hang of it.  In my mind's eye, I had a vignette of many folks who came before me, installing tubes.  I pictured repairmen with--what I think they had--a tube caddy, full of tubes separated by cardboard dividers like bottles of wine.  

I didn't bother to clean the somewhat oxidized-looking tube pins, which were much darker and tarnished than the 2016 Chinese Primaluna 12AU7s.  I rolled one set out, and dropped the other in. 

It was interesting to see the Amperex tubes flash up on startup.  I wondered if they were going to blow!  They flashed brightly and calmed almost as fast as they lit up.  My pessimism nearly expected the amp to signal that I had a bad tube or two.  Primaluna's autobiasing automatically kicks in and handled that--just like Mesa Boogie guitar amps.  

Things sounded just fine out of the box. I'd say no better or no worse than swapped tubes.  I've been running them now for 90 minutes.  The difference is real yet subtle. Here's what I think:

--The Amperex tubes have more top end attack.  I wouldn't call it bite. There's more detail on top....not much, but it's there. 
--The Amperex may be less warm.  The bass seems to be more defined but there's less of it. 
--The Primaluna's sounded a bit bloatier, which was kind of nice in some ways, yet in another it's making me thing and digest these differences. 
--While the soundstage of the Amperex seems to go back deeper than the Primaluna, it seems like I'm sitting a bit farther back from the performance.  I cannot tell which I prefer.

I haven't had a chance to really crank the volume and get them heated up and pumping.  

I have no strong takeways from this experiment yet and I certainly haven't decided which I prefer.  Next up is a set of 6 Ciftie military grade set of 12AU7s.  

Different indeed!