Vacuum Tubes

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Please note that there are hundreds of different models of vacuum tubes. All one need do is to run an internet search on "Vacuum Tubes" and a number of different mom-and-pop internet stores will be included in those search results. Those stores will have all kinds of tubes that you've never heard of and, unless you go searching for them, will never hear of again. Chances are you don't know about what a 12AX7 is, let alone a 6X4. There's a 6AQ5? A 6EU7? A 6C4?

As it turns out, in 1962, Gibson came out with a redesigned GA-5 "Skylark" amp they retitled "Crestline". The Crestline Skylark uses NONE of the tubes that are commonly in use today. It was built with one 6X4, one 6EU7, one 6C4, and two 6AQ5s. The simple fact of the matter is that there is no heavy music tube amplifier, that is made today, or was made 40 years ago, or uses the tubes that the Crestline Skylark was manufactured with (it's a 5-watt amp).

The point is that for the purposes of tube amplification, of all the tubes that have been created, only a small fraction have found their way into use in heavy music instrument amplifiers. We've endeavored to list those tubes and to provide some technical understanding regarding the tubes and their uses.

Preamp Tubes

Preamp tubes are used in the preamplification phase of an amplifier. Interestingly, preamplification can be thought of as just another stage of amplification. What makes preamplification different is that a preamp takes an instrument-level signal (-10 db) and amplifies it to a line-level signal (+4 db). A power amp needs a significant enough signal in order to power loudspeakers for playback or performance.

A typical instrument amplifier contains both a preamp section and a power amp section. The same tends to be the case for all musical equipment. A singer usually sings into a mic preamp that then goes from the line level into a P.A. (public address system) that has the power amp.

Side Note 
What makes effect pedals different from rack effects tends to be where, in the signal chain, the effect is sitting. In other words, what makes a pedal different from a rack effect is in what decibel level the signal is at when a pedal or rack effect is applied. Effect pedals typically accept, modify, and output instrument-level (-10 dB) signals. Rack effects typically accept, modify, and output a signal at the line-level (+4 dB). This means that it's usually not possible to use pedals in the effects loop of amplifiers. Of course, there are exceptions. There are so many that it's not possible to list here. The point is that if you attempt to put your stompboxes in your effects loop, don't be surprised if it sounds bad. Effect pedals are usually designed to accept a -10 db signal, not a +4 db signal coming from the effects loop. (There are ways around this...)

Preamp Tube Types

Power Tubes

Power tubes are used in the "power" amplification phase of an amplifier. This is where the line-level signal is amplified to push a loudspeaker (or a number of loudspeakers...). (The linked article on Power Tubes will have much more information)

Power Tube Types

Rectifier Tubes

The purpose of rectifier tubes is power rectification. Rectification, in an amp, is the act of converting the alternating current (AC) coming from the power transformer into the direct current (DC) that the amplifier can use. Nowadays, rectification is done using diodes. The diodes are aligned, usually in a 2x2 configuration that's called a "bridge". Before diode bridges were used to rectify the high-voltages from power transformers, tube rectifiers were used. Tube rectifiers have a certain sound associated with them, a softness to the guitar attack, that you can't get with diode bridge rectifiers. However, tube rectifiers also tend not to be able to handle current loads beyond 50 watts. Guitar Player Magazine has a good article on rectification. For a deeper and more in-depth description of Rectifiers please see the linked sources.

Rectifier Tube Types

Tube Manufacturers

There have been and are many tube manufacturers. In the 1980's and 1990's it was thought that the vacuum tube, and vacuum tube-based amplification would be something that would be gone by 2020. The irony of the Internet is that the "new" technology of information sharing has allowed a revival of interest in the "old" tube technology. Below is a list of the most common or best well-known tube manufacturers.

Additional Sources