I have a conrad Johnson pv12 preamp which uses a pair of 12au7 tubes and my favorites I tried were a matched pair of old NOS Brimar CV4003 tubes I got a few weeks ago. They sound lovely and well worth the money IMO ( very hard to find in the US and werent cheap). I also was using NOS pair of RCA cleartops which sounded quite good before that (somewhat expensive but half the price of the Brimars). There were some stock tubes made for primaluna in it when I got it from my friend and I can say they didn’t sound nearly as good as the old NOS tubes I bought. The RCA and the Brimar sound way better. That preamp had old mullards when he bought it used many years ago and they sounded very nice too. They were old and had a lot of hours on them and started going bad so he got those other tubes from a primaluna dealer. After he had a chance to buy a very expensive PBN Olympia preamp that was a little over 5 figures new (from a guy he knows at a price he couldn’t pass up) he sold me the CJ for a nice price and it pairs nicely with my old CJ amp

I love CDs and records. All I play on the home stereo

I leave mine on. I have the revel Performa M20 speakers and the material is thin. I don’t hear any difference on or off. I leave them on since they are in my bedroom and I’m clumsy lol