Are your output valves matched for your amp? Just because a set of valves says “matched” doesn’t mean it’s matched for your amp. Most valve suppliers put a sticker on the valve showing the anode current and the Gm. But what were the test conditions? So you might think they must be matched. Not necessarily the case. In the UK, a number of suppliers use and maintain venerable testers such as the AVO Mk4 that

Some folks find they can hear the valves rattling in their 6V6S-loaded amps. Usually with specific notes. I see reports of Fender Re-Issue Princetons and Deluxe Reverbs having rattling 6V6 valves. This rattling sound does not come through the speaker but is actually the mechanical parts inside the tube which you can hear. The tube internals resonate when you play specific frequencies. As it is acoustic rattling, this effect is usually only audible in quieter