They're primitive technology, but then so is a Stradivarius. Despite technological wizardry a half-century beyond tube technology, tone purists universally agree that the fat, warm presence and gravelly distortion of a genuine tube amp can't be beat. Unfortunately, tubes can be temperamental and are far less stable and long-lived than their solid-state counterparts. Like a fine automobile, a tube amp requires a little TLC to keep it in the groove.
Warm up and Handling Most tube amps these days have switches that let you put the amp in standby mode before you nail the tubes with a lot of juice. Hit this switch a couple of minutes or so before you begin to play. This warms up the plates slowly so you don't have hot current hitting a cold tube. Barring a standby switch, go easy on your amp when it's just waking up, and the tubes will last longer.
Solid state technology can take a lot more bumping and jostling than a tube rig. Tubes can shake loose and can be damaged by shock. So you may want to handle your tube amp yourself rather than leaving it to the drummer's kid brother.
Tubes are odd critters, sometimes if handled correctly preamp tubes in particular can last 30 years. They can grow warmer and begin to break up easier over time. Or they can go bad in a year or two and screw everything up. Generally, if you're happy with the way your amp performs, don't go messing with the tubes. But if your amp is acting up, don't assume that the tubes are not the problem just because they are relatively new.
When To Change Power Tubes You should think of changing the power tubes in your amp (the larger tubes) the way you think of changing the oil in your car. If you run them hard and long, you'll need to change them a lot. Generally, if you play an amp a great deal you will need to change your power tubes at least once a year, considerably less if you don't play the amp much.
If your power tubes are beginning to go, you'll probably find that the amp is not as loud. If the intensity of the tone seems to sag and evince less presence, it may be a sign a power tube is going. Soon you'll be turning your amp up to 7 to get the same volume you used to get at 5.
Funky electronic noises and pops can also be a sign of power tube failure. Or sometimes power tubes can become microphonic. They may begin to emit an unpleasant, extremely high-pitched constant squealing. Next week we'll discuss preamp tube problems that can have similar effects, but if you're hearing these symptoms, chances are you'll have to bite the bullet and buy yourself a new set of power tubes.
What Tubes To Buy When you change tubes, stick with the specific type of tube recommended by the manufacturer (i.e., the type included in the amp when it's built). Switching out types of tubes (say an EL34 for a 6L6) is a great way to destroy your amp. Tubes available directly from the manufacturer will usually be best suited to your amp. If you begin to use tubes from other companies such as GrooveTubes and Ruby, it's best to take your amp to a pro and have it biased correctly for the particular tubes you've purchased.
GrooveTubes and Ruby have reliable, realistic grading systems that let you know precisely the type of tube you're buying. So as long as you buy that exact kind of tube each time, you don't need to worry about having your amp biased again. You will want your power tubes to be matched in terms of output, so it's best to buy them in pairs or groups.
To tell whether your tubes are biased correctly, look at the color that the tubes glow when they're fired up. The tubes should glow a soft orange/amber. If they're a sort of purplish blue, they're being underdriven. If they're a harsh white/yellow, they're being overdriven. This latter condition is bad. It could really screw up your amp.
Next week we'll discuss the preamp tubes and tube amp troubleshooting. Meanwhile, play hard and play GOOD!
Troubleshooting Preamp Tube Problems If something goes amiss with your tube amp, in all probability the problem is with the tubes themselves. As you would expect, the little tubes are for the preamp section and the big tubes are for the power section. Preamp tubes can last much longer than power tubes. They're also a whole lot less expensive and can be changed individually in a pinch, whereas all of the power tubes should be changed at once.
Since preamp tubes are cheap, it's a good idea to have a full complement of replacement tubes on hand. Finding a tube tester these days is only a little harder than finding the lost chord, so changing out tubes for new ones is your only practical option for testing. If you can't fix the problem, you can at least determine that you need new power tubes before you lay out for them.
Before you go digging around in the back of your tube amp, make sure it's been turned off and unplugged from the wall for at least ten minutes. There are a two nasty things it can do to you. Most obvious is burning. There's generally a lot of heat happening in a tube amp, and it might take quite a while for it to dissipate. Try touching the tube lightly to make sure it's cool before you grab it and become an instant heat sink.
A tube amp can also give you quite an electrical jolt-enough to kill you if you're astoundingly unlucky. That's another reason why you should be sure it's unplugged. Even unplugging them won't make certain vintage amps safe. The filter capacitors in some old amps can store a monster charge for days at a time. But you have to have the amp apart and really be digging deep to encounter this. As a general rule handle the tubes carefully, don't go poking around too much inside, and you'll be fine.
The following are some common problems that can result from bad preamp tubes. Be aware, though, that flagging power tubes can create a lot of similar problems. If new preamp tubes don't do the trick, it's probably time to change out your power tubes.
Unwanted distortion-When preamp tubes begin to go, they might start to break up even when your amp is on the cleanest setting. The most likely culprit is the tube closest to the power tubes, since the other preamp tubes cascade into this "driver" tube before the signal goes to the power tubes. Ideally, you should replace all the preamp tubes at once, but in a pinch you can often replace this one tube and solve your problem. On the other hand, some guys who want distortion all the time like it when preamp tubes age and break up very easily. Misbehaving EQ knobs-Since the EQ is handled in the preamp section of your amp, any problems with them-such as generally having very little effect-is probably due to a bad preamp tube. Weak, buzzy signal-If the signal seems anemic and prone to noise, the problem may be the preamp tube closest to the instrument input. The job of this tube is to handle the initial boost of the signal. Dead reverb-In older amps, the reverb is often a tube function. If you have one of these vintage gems and the reverb dies or gets very funky, it's probably a preamp tube problem.
Other Common Issues Another tube problem you might encounter with a vintage amp is a dead rectifier tube. After about 1968, rectifier tubes were replaced with much more reliable solid state units. The rectifier is a larger tube that's generally located on the opposite side of the power tubes from the preamp tubes. If it's dead you'll get no sound at all from the amp.
It's worth mentioning that you can create serious amp problems by mismatching your amp and speaker. It may sound like a cool idea to bypass the speaker in your vintage combo and run to a separate cab. But if your amp is rated to 4 ohms and you wire into a 16-ohm cab there will be trouble. It might even sound great at first, but you will kill your tubes in very short order. Also, make sure that you use adequate gauge speaker cable when connecting the amp to the speaker. Small wire is less reliable and puts extra resistance on the tubes.
Know Your Limits If you eliminate all of these problems and still can't get the amp to work right, take it to a pro. Especially if you have an expensive vintage amp, it's worth it to pay a little extra and have somebody who really knows what they're doing set things up.
Whatever you do, don't let these possible problems scare you off from genuine tube amps. By and large if you play a moderate amount most tube amps will require maintenance only once in a long while. And the rich, vibrant tone real tubes deliver make the extra care well worth it.
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