Hi Guys, I know there is probably a lot of different posts on this topic already but I'm finding different answers everywhere I look. So this is my very first tube amp and I've have had it for around 5 years or so and never needed to replace the tubes in it until now. About a month or so ago, the amp started to randomly crackle while I was playing and and I noticed that when it did crackle, the one power tube would flicker. Now if I try to use that tube at all, it red plates after the amp is on for a few minutes and if I switch tubes, the same tube red plates so I know it has to be the tube that is bad. I also took my pre-amp tubes into my local music store and was able to get them tested and my one pre-amp tube has a bad plate in it. So in the end, I'm thinking of just replacing both pre-amp tubes and both power tubes. Now from what I've read so far, the power tubes need to replaced together as a matched set and need to 6L6s while the Pre-Amp tubes can be replaced individually just as long as the are the 12AX7s. Now here is where my questions come in at, do the power tubes have to be replaced with the Sovtek 5881/6L6WGC tubes or will any 6L6 tube work and does it have to be the 5881 version? And also do the pre-amp tubes have to be replaced with the Chinese 12AX7-B or will any 12AX7 work? I was told by a good friend of mine that Mesa Boogie Tubes are pretty well built and have a solid tone to them so I was thinking about just getting the their 6L6 STR-440s and either 12AX7s or the SPAX7-A for the pre-amps. Any and all information will be greatly appreciated. As I mentioned before, this is my first tube amp I've ever bought so I'm learning all of this new information for the first time. Now I do know that once I get the power tubes, I need to re-bias them which I've already learned how to do thanks to the wealth of information on the internet. I'm also kinda curious as to why my one current tube would be red plating regards if I put in the V3 or V4 sockets? I know very little about tubes so I don't know if its the cathode resistor or grid resistor (if either of those two things exist in a tube) that crapped out or if it might be something else in the tube. I know this isn't really important to know but I've just one of those people that likes to obtain as much information and like to learn how things work and operate.