Schiit Freya + Class A in Stereophile

I put some CBS Hytron tubes in the input stage side and it really made the preamp a whole lot better. 

When I read the Stereophile test, the first thought I had is why they didn't roll some tubes. 

The Freya plus response well with tube roll, the better the tube the Freya improves, Iam using pavane 6sn7 and tennis ball pavane 6sn7.Though the JJ 6sn7  also does a good job.Its worth also upgrading the pc.iam happy with Freya, though originally I want audio research, backert preamp.

I just swapped out the Freya+ for a PrimaLuna EVO 100 preamp. But that aside, I just wanted to mention that I do subscribe to Stereophile primarily to see what the reviewers use for their music testing and to discover new music from the back section of the magazine. I find it helpful to listen to what a reviewer used for testing and to see if I can't hear what they heard as well. 

I noticed when I rolled in some NOS Sylvania tubes the Freya + sounded much better. It sounded very good with the stock tubes, but the NOS tubes improved performance noticeably. It replaced a SS Parasound preamp which was no slouch. In terms of overall sound quality, I rated the Parasound a 6 out of 10 and the Freya was an 8.5 out of 10. I must add I don't buy really expensive audio gear simply because I can't afford it and I have a ceiling amount I am willing to pay for any piece based upon practicality and reasonableness. So I find the Freya a very good audio preamp for the price.

For a newbie, could any of you please list the exact tubes you've upgraded to that have been a really nice upgrade?  (also which tube position they are?)