Given that a cartridge is a mechanical device it would not surprise me that it needs a bit of wiggle time to get sounding right. It's just like warming a car engine. The difference here is a car engine will warm if idling but that does not seem to be true of tube gear. Tubes seem to need to actually have more electrons flowing from the cathode to the plate than is possible with just the bias current. I've heard that a "cloud" of electrons will develop inside the tube. I wondering if listening to music either creates the cloud or does it "burn off" the cloud ?
Just as a FYI... I've been away from audio for some time now and have just gotten back into it... I use to be into fairly serious amplifier tweaking (all the basics cap, resistor, and PS upgrades plus full circuit redesigns). During one of my mods I built the circuit completely wrong and before the amp thermally shut down I was convinced I had made a huge improvement. To make a long story short I began to think that I was full of it and just hearing what I thought I should be hearing..
So now I'm in the process of setting up a HT system in dedicated HT room I'm less critical about HT.. how different can one explosion sound from the other.. for me HT is mostly about power. I get way too distracted with the video and the story to really listen to a movie. HT gear such as Rotel is fine for me. The bottom line was that gave me a chance to swap around some amps. The need for my wife and kids to have a nice place to watch movies is what brought me into the tube world. To be honest, (not to open another touchy subject) I've never noticed differences in many of the standard tweaks (interconnects, speaker cables, power cords, etc). From my standpoint as long as it is reasonably hi-end it is fine with me.
So back to the topic... for me to hear such a huge difference is really a little freaky. Over the last few years I've become a hardened (indifferent?) skeptic. I had way more important things to do with my time that fart around being an audio geek again :^) I went to the store mostly trying to decide on either a NAD or Rotel HT receiver. I then got the idea that I might as well go with separates and upgrade my two channel system in the process. In fact when I demo'ed the CJ amp I was not really that impressed.. My dealer had a once a year demo sale so I decided to take it home an return it if I did not like it. I bought my tube gear because I needed another amp and figured what the hell let's give tubes a shot they look cool and retro is so hip these days :^) Almost any reasonably high-end amp will sound great so let's just pick up another amp.. I was not even unhappy with my old amp! I was not on the quest for the ultimate sound I just wanted a new toy... so I did the typical research... reading ... listening.. etc. and decided on CJ . This has turned into a long winded response but the fact is if I actually hear it, it must be a huge difference... Oh no I've turned back into an audio geek... My wife would say why qualify that statement...