I have a Mesa Lone Star 100W that is a fine amp. My #1s are the HXDA and DG30, and I've equipped them 100% with NOS tubes. I loaded the preamp of the Lone Star with NOS GEs and an RCA in v1, and yes, it was a big improvement, but I didn't want to blow nearly a grand on a quartet of NOS RCAs, Sylvanias or GEs for this amp. I've previously retubed the output tubes and rectifier tube twice. I each case the Mesa brand Chinese tubes Mesa had blew or had noise issues. These Chinese tubes also rattled like crazy! I had to buy tube damper rings to stop the rattling (from Eurotubes, and yes, they work). I decided to try the JJ 6L6s Mesa now brands and sells, but I remembered that Telefunken works with JJ to hand select their tubes, and then they cryogenically treat them. Telefunken makes some very high end microphones based on classic designs, and bought the name. I'm usually against doing that, but the mics are absolutely killer, and their top ones are very expensive (and sound the part). I figured, wtf, they weren't that much more than Mesa was charging for their JJs. I bought a quartet of them. Cryogenics for tubes could be BS - or not. The process was invented to change the strength and stiffness characteristics of metal, and is used in industry for that purpose. I haven't tested the stock JJ tubes. I have no idea if they'd sound like the ones I installed. They might sound exactly like the Telefunken brand ones, or not. It doesn't matter, of course. If I blew an extra little bit of coin to make myself happy, I'm good with that. These tubes truly improved the tone of the amp, and they do not rattle AT ALL like most modern tubes do in a combo. they have a tight bass response, a very nice, crisp high end that doesn't take your head off, a great midrange with lots of balance, and they break up nicely when the amp is driven. And at 100 Watts, driving the Lone Star into output tube breakup is...um...loud...but hey. It's all about tone. The amp sounds a lot better, and now I like it 85% as much as my PRS amps - and I LOVE my PRS amps. So that's saying quite a lot. If you're of the opinion that these are just rebranded JJs and that the cryogenics is BS, I'm good with that. What I can say is that I've got good results!