Hey, I hope this is in the right section-- I apologize if it isn't! Anyway, I wanted to share my experience swapping tubes for the first time. I've always been nervous about opening up and pulling components out of my amplifiers, but now that I have a particular amp for performance and one for practice, I'm okay with accidentally messing one up. Luckily, it didn't come to that. I'll also say that I've been a sort of a tube skeptic, in that I never really believed that changing tubes would give me much of a sound difference. It was at the prompting of a friend that I ordered some up to play with. The amplifier that went under the knife for this experiment was a Hughes and Kettner Tubemeister 18. My first tube amp. It came stock with Chinese EL84's and 12AX7B's, two of each. I had found no faults in the sound of the amplifier, but ordered up a couple of tubes to play with. The first ones I switched were the power tubes. I put in a couple of matched Tung-Sol EL84's, which were a little bigger than the stock ones, but still fit just fine. I didn't hear much of a difference here, but I doubt that I was driving the power tubes to distort. They also heated up REALLY FAST, and I'm impatient, so I left them in and moved on to the preamp tubes. I had ordered a Sovtek 12AX7WB, since it seemed like a pretty standard example of a 12AX7, a Sovtek 12AX7LPS because it's description said it was a good phase inverter tube, and a Sovtek 5751 to play with preamp gain. I took any suggestions in the product description and on the internet as good, since I know very little about these types of electronics. I put the 12AX7LPS in V2, which I assumed was the PI position, and left it there. I didn't try any other tubes in that position. I started with the 12AX7WC in V1. It was actually much different, to my surprise. The H&K's have a reputation of being biased towards the highs, which I like-- that's why I use 'em! This combination of tubes darkened the tone noticeably. I probably could have compensated for it in the EQ section, but I left all the controls in the same place for the test to hear the difference. It also seemed to have less punch than the original Chinese 12AX7B. Next I swapped in the 5751. I liked this one a lot. It didn't darken the tone at all, and it seemed even clearer than the original Chinese tube. I chalked this up to having 30% less gain, but it could be something else. A/Bing this one with the Chinese 12AX7B, I had the impression that the Chinese tube packed more of a punch than the 5751, but the balance of the tone was very similar. For general playing, I actually liked the stock tubes best. But the 5751 in V1 and 12AX7LPS in V2 sounds very nice. I left that combination in, along with the Tung-Sol EL84's, and will continue playing with them to see what new sounds I can discover. Overall, a fun time! Even though the differences weren't earth-shattering, I could definitely tell that there WAS a difference, which is more than I expected going in. I'll probably notice more subtleties as I continue playing with the new setup. I'm going to leave my performance amp, an H&K Grandmeister 36, all stock. Since it uses presets, I'd probably just tweak them back to what they sound like right now! I'll use the tubes I took out of the Tubemeister 18 as backups, though, since they're the same as the ones in the GM. And that's it! Hopefully this info can help someone somewhere, but I guess it's mostly a chronicle for my own benefit. If anyone has any questions or suggestions, I'd love to hear them!