Valve Guitar Amplifier – Tube Operation Explained

Guitar Amplifier Tubes or Valves Operation Explained: You will hear people talk about Valve amps and Tube amps. They are the same with the valve being a European term and the tube being used in the USA. From the 1940’s until the 1970’s tubes were used in nearly all electronic devices, such as TV, Radio, Stereo Systems and of course Guitar Amplifiers. With the introduction of low-cost, low-maintenance semiconductor transistor systems, the tube became less desirable for manufacturers and consumers. This allowed for the design of cheaper, smaller and reliable products but cheap is not always best. Most guitarists feel that guitar amplifiers with tubes provide better tone and tone control, when compared with transistor amplification systems.

Vintage valve guitar amplifiers and earlier guitar amplifiers that today would be considered as practice valve guitar amplifiers due to the low output power are still sought after and change hands for considerable amounts of money. Companies like Fender, Vox, Marshall and Supro have produced combo valve guitar amplifiers that have shaped the iconic tones of many famous guitar players from the 50s, 60s and 70s. Jimmy Page used a 5W Supro valve guitar amplifier in the stidio to record many famous Led Zeppelin tunes.

Yuma Gold Amplifier Valve
Yuma Gold Amplifier Valve

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.

The Guitar Pick Up Output Signal

Your guitar pickups sends sound out through a cable as a weak electric signal. That signal enters your valve guitar amplifier via the input socket and is routed through the vacuum tubes where electricity causes the heating element in the tube to get hot. This heat then causes the cathode to release negatively charged electrons. 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.

Yuma Gold 6V6GT Guitar Amplifier Valve
Yuma Gold 6V6GT Guitar Amplifier Valve

You probably noticed that guitar 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 back of your guitar amplifier. You will see various valves, some small and some larger. The smaller tubes are part of the pre-amplifier stage.

Heater and Standy

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. 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.


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.

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