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Amplifier Tubes Explained


The term 'tube' is U.S.A. slang for 'electron tube' or amplifier tubes. Some people use the European term, 'valve'.

From the 1940's until the 1970's tubes were used in nearly all electronic devices, such as: Television sets, Radio's, Hi-Fi's (now called Stereo Systems), and guitar amplifiers. With the introduction of low-cost, low-maintenance transistor systems, the tube became less desirable for producers and consumers... except for amplification. Many people feel that amplifier tubes provide better tone and tone control, when compared with transistor amplification systems.

SIDEBAR: As a child, I remember visiting the local hardware or drug store whenever our TV-set acted weird. The TV picture might have horizontal bars running through it, or wavy lines distorting the picture. The problem was nearly always a bad tube. My father would pull the set away from the wall, unplug it, and pull a group of tubes out. They would go into a paper bag, and off we'd go to the store, where each would be inserted into a unique tube-tester socket. A gauge on the machine would indicate if the tube was OK, or bad. With the new tube in hand we'd head home to replace each in it's socket. Voila... Ed Sullivan standing straight up again!

Basic Amplifier Tubes Explanation...

Tubes amplify or alter sounds by converting heat into electricity. As more electricity is produced, the volume from your loudspeaker increases.

A tube is similar to a light-bulb... A glass housing seals the components in a vacuum.

The basic components in amplifier tubes are a heating element next to a cathode, a grid, and an anode. The grid separates the cathode from the anode.

Your guitar pickups send sound out through a cable as a weak electric signal. That signal enters your amplifier and is routed through the tubes. Electricity (AC electricity, the kind that comes from the wires in your house) causes the heating element in the tube to get hot. The heat causes the cathode to release negatively charged electrons (for those who care... this is now DC electricity).

The grid controls the flow of electrons. The various tube grids are controlled by the knobs or dials on the front of your amplifier. The electrons passing through the grid are collected by the anode, and then pass out of the tube. The resulting increased flow of electricity yields an amplified signal from your guitar.

This boosted electric signal, when sent on to the loudspeakers, allows you to hear your guitar at various volume levels.

In addition to strict amplification, some amplifier tubes are used to modify your guitar's signal, resulting in various tones or effects.

You probably noticed that amplifiers with tubes can feel hot, and you can sometimes see an orange-red glow inside. Both are caused by the heating element in the tubes.

You can tell power is flowing to a tube when you see this glow, but the glow does not necessarily mean that a tube is working. The cathode, the grid, or the anode may be defective even though the heating element still glows.

The first stage of amplification boosts the input from your guitar only slightly. This is called pre-amplification. The tubes used for pre-amplification produce less energy than the power tubes.

The power tubes are where the real amplification occurs. These pump out large quantities of electricity for driving loudspeakers.

You should be able to tell the pre-amp tubes from the power tubes by looking into your amplifier. The smaller tubes are part of the pre-amp.

Remember that a key component of a tube is the heater... so amplifier tubes have to warm up before they will work. You may have noticed that if you turn on a tube amp and immediately strum your guitar, there is no sound. The heating elements have not warmed the cathode's yet. Until they do, no amplification takes place.


Beware! Tubes inside amplifiers get VERY hot and produce LETHAL levels of electricity. NEVER handle a hot tube and NEVER reach inside an amplifier that is turned on.


Some amplifiers have a 'Standby' mode. When in Standby, the tubes are heated but the output of the amplifier is turned off, effectively muting your system.


Amplifier Tubes Care and Maintenance

Tubes should to warm up for a minute or two before they reach operating temperature, and stabilize.

Don't move a hot tube (i.e., don't move a tube amplifier until it has a chance to cool down). If you do, you shorten the life of the tube.

Never handle a tube with your bare hands... Wear cotton gloves, use an old T-Shirt, washcloth, or other soft cloth. Touching a tube with your bare hands is like touching a halogen bulb with bare hands... the oil from your skin gets on the glass and creates a hot spot. The hot spot can cause the tube to crack or shatter. Handling amplifier tubes with cloth can also protect you hands if the tube breaks.

Do yourself a favor and replace your power tubes with the exact tubes you pulled out of it! If you don't, then you have probably changed the flow of electricity inside your amplifier. To prevent damage it must be re-balanced (this process is known as "re-biasing" the amp). This is a job for an experienced technician. It's expensive, but required if you change the power tubes. You probably do not need to re-bias pre-amp tubes, check your owner's manual.


Are my Amplifier Tubes Dying?

There are a few tell-tale signs that a tube is weak, and ready for replacement. Of course, not all amplifier tubes are so thoughtful... some simply burn out without warning. But for those that die slowly, here are a few of the warning signs.

If you need to change a tube, check your owners manual, or the manufacturer's web-site first. It may give tips on identifying the problem, removing the old tube, and obtaining the proper new tube.

Also, even though it drives up the cost, you should change an entire set of tubes at the same time. So, if one pre-amp tube must be replaced, change all the pre-amp tubes. If you don't, the life-span of the new tube is reduced.

One more important note: Tubes don't unscrew, they pull out... like a cork in a bottle.

Do you need replacement tubes? Check out




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