Tech Tip:Proper Care and Feeding of Tube Amps
First, you should try to make a habit of firing up your amp in Power/Standby mode for at least one minute before pounding the current completely to all tubes. This way, when the tubes get the full jolt of electricity, the plates are nice and warm. Hot current hitting cold tubes is one of the worst things that can happen to a tube amp. Using the warm-up procedure can really extend the life of your tubes. Switching the amp to standby for breaks also helps extend tube life. There are very good reasons tube amp manufacturers put standby switches on their amps. Using them properly is the best thing you can do for your amp.
You can tell if you're firing up your amp properly when you're quietly strumming your strings, waiting for the tubes to come online. If you have a fully audible signal and hear the notes clearly the instant you hit the switch, you're doing the right thing.
Some players recommend changing tubes almost annually. I've owned tube amps for years and have never yet changed a tube or had one go bad. Actually, moderately worn tubes sound better than new ones and, if properly cared for, just keep sounding better and better. I have to give credit to the folks at Mesa Boogie for teaching me these tube amp tips nearly 20 years ago. (Note: Mesa Boogie still offers this advice in their new owner's manuals.)