To get the most life out of your tubes you should warm them up before playing them. Don't leave the amp on forever because the transformers have a 112 degree F ceiling, and no way to cool down unless the amp is off. As far as longevity of the transformers go, 2 hours on, OFF not standby while you take a break, 2 more hours of on-time. Back to tube longevity. Different tubes have different warm up times. Pre-amp tubes like the 12AX7A take 13 seconds, output tubes take about the same time in most cases. They take longer to warm up as they wear out. So giving them 30 seconds should do. If they play loud and clean when you take the amp off of "standby" then they were ready. Other exceptions are the EL84/6BQ5, and my favorite rectifier the GZ34/5AR4. The EL84 takes about 45 seconds to warm up. The GZ34 takes longer to warm up than any of the other tubes do, and that is by design.
The GZ34 is a slow-start rectifier tube. It's job is to convert the high AC voltage into high DC voltage. Most standby switches disconnect the DC high voltage from whatever rectifier there is in the amp from the other tubes. It would be beneficial to any amp that does not have a standby switch to use a GZ34 rectifier tube. It is pin compatible with the most common rectifier tubes. Any issues would arise if the pin basing were different of if the GZ34 drew more heater current than the other rectfier type. In most cases it's close enough and the power transformer can handle it with out over-heating. The advantage of the GZ34 is mainly that it warms up after the other tubes do, eliminating the need to have or use the standby switch completely. It happens to have just enough compression to please me, greatly.
A lot of Fender amps use a GZ34 at one point in time and then a 5U4 at another. If you use the GZ34 in the amp without a standby switch tubes will last longer because they will not suffer from "cathode stripping." The 5Y3 also has the same pin basing.
Now the biggie no one ever told you about. You need to let your amp cool down for 3 minutes before you move it! A normally functioning tube amp will have bulb temperatures over 300 degrees F. It takes 3 minutes once completely powered down to reach 140 degrees F. Scalding hot is 180 degrees F. The tube is like a light bulb (vacuum, filament), and both undergo changes in shape and in flexibility as they cool. As the filament cools it also becomes more brittle, so if you move the tube as it is transitioning from its' orange hot malleable state to its cold brittle sate you stand a good chance of wrecking the tube. And it not only the heater that behaves this way, but the rest of the electrodes too. The screens get hot too, and I've seen plenty of screen wires get loose in the tube and short out to something else.
So tell your tour manager, the tube amps get switched off first and taken off stage last.
Who makes the best GZ34?