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?

At this time, Groove Tubes actually does make tubes. They have purchased the original tooling to produce US made 6L6s' and are manufacturing these in the USA. They also make an import KT66 and one particular 12AX7, useing gold in the construction of the control grid. That's all they make at this time. The rest of their tube line is, as it always has been, a representation of all the worthwhile tubes made, mostly currently. They, like Fender, Marshall, Mesa Boogie, Ruby, TNT, do a very good job of screening out the bad tubes and putting their own name on them. To the best of my knowledge, Groove Tubes is the only one on that list who manufactures any tubes, and that represents only a small portion of what they offer. Fender is now shipping "Fender Groove Tubes'" in their amps. All the ones I've seen still carry a third name, the name of the actual manufacturer: Sovtek.

Marshall has dropped Sovtek from certain model amps, and is currently shipping Svetlana tubes in
their amps (pronounced Sevitlana). Prior to that they had used Tesla tubes for a long time, and are currently made also. EI was apparently on the wrong end of Western politics, and the manufacturing plant in Yugoslavia fell down, went boom. Its production of tubes rises and falls to this day. The highly abused Chinese Sino 12AX7 was the tube everyone loved to hate, while at the same time widely used or the production of new amps. The tooling is said to have been put outside, and has gone to rust. I guess another form of friendly fire. 

There is more than one tube manufacturer in China! Lets not lump everyone together unfairly. Just like there is more than one Russian tube company, there are few enough choices in tubes to start getting a National Bias (is this a joking matter?). For anyone who cares, there is a market for American made tubes, as proven by the gentleman who purchased the tooling and licensing of the name from Westinghouse - who is making the 300B in the good old USA. The import 300B's sell for up to $300, so it's a fair guess the American made Westinghouse will cost more. By the way, the 300B is IT for true hi-fi. If you want to buy a guitar amp that uses this 42 watt triode please tell me.



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