I figured I should try to contribute something to this site. I got a brand new fender champion 600 and i compared 3 power tubes:
1)stock no-name chinese tube
2)vintage blue bottle 6v6gt (procomm?)
3)vintage rca 6v6gt
I played four clips with each tube. There are two clips contained within each sample below. Two with the volume at 12 o clock and two with the volume dimed. I played a neck pickup and bridge pickup sample at each volume setting. Mic was a 57 on inch off of the grill cloth at the outer edge of the dust cone. 57>art pro mpa>firepod>logic. Guitar is a fender 69 reissue tele thinline. Preamp tube is the stock chinese tube. Let me know what you think.
Disclaimer: this is not meant to be a super scientific test. I know the art pro mpa isn't the ideal pre for a job like this but i think that the differences between the tubes are pretty easy to hear regardless.
I was really surprised to hear how un-subtle the differences between the power tubes were. I think my favorite was the rca. I'm surprised by that because I have a couple laying around the house and I was told that the blue bottle can be worth a lot of money.
Thank you for the test. I like to use small amps for recording and have recently been considering getting the 600. That 2nd QoTSA riff really pairs well with this amp, with any of the three tubes. I liked all the tubes for different reasons. With the low amp price, it's feasible to have more than one of them and have each one tubed differently.