Short for Vacuum Tube, a device used to drive amplifiers until the advent of transistors. A tube works like a flood gate, except with heat. A small heater in the base warms up, while a gate like mechanism opens and closes depending on the input signal. As heat goes through the "gate", it is turned into electrical energy. Tube slots must be biased, which determines the voltages seen by the tube. Only guitar amps still use tubes (as well as some bass amps, mic preamps, and other pro audio devices.)

Though a true discussion of tubes is enough to fill a large book, let alone a short definition, but here are some more common types of tubes.

Preamp: American name (European name) Other name
12AX7 (ECC83) 7025
12AT7
12AY7

Rectifier
5U4 (GZ32)
GT5Y3 (GZ30)

Power Amp
6L6GC
6V6GC
EL84
EL34
KT66
6550
The Ampeg STV had a whopping six 6550 tubes, producing 300w @4 ohms!"
by Contraceptive SpongeBob December 1, 2005
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OK, I just want to clear up the previous definition for an Electron Tube (the type used in guitar amps and high-end audio applications). The fella before me said tubes convert heat into electricity, this just goes to show that a little knowledge is a dangerous thing. Tubes do have a heater element, but this is seperate from any signal processing the tube performs. Tubes have anywhere from 3 to 5 elemets inside, not including the heater. The first is called a Plate, this is a metal plate with a given DC voltage applied to it, usually 200 to 400 volts. Another part is called the Cathode, this is connected to ground, sometimes through a resistor or capacitor network. The voltage "wants" to flow from the plate to the cathode, but between them is a "grid." The grid is connected to the input signal and as the signal changes from a positive charge to a negative charge (all musical signals are AC current, oscillating between + and -)it allows more or less of the plate voltage to flow to the cathode, resulting in a large voltage swing on the plate in time with the input signal: the amplified signal. The other elements go between the grid and the plate and serve to make the tube more efficient, these "screens" as well as the grid can be biased, that is, they have a fixed voltage applied to them to more carefully control how much current flows through the tube.
There is a heater element in the tube as well, very similar to a light bulb filament, but this only warms up the other components so that the tube can work better, this is analogous to putting oil in an engine. Tubes absolutely do not convert heat into electricity, I don't know if anything can convert heat into electricity unless you count a gas powered electrical generator, resistors convert electricity into heat, but that is another story.
Overbiased tubes will blow out because there is too much current flowing from the plate to the cathode, while under-biased tubes will have low output and sound thin, bitch.
by Nyquist Rocked June 6, 2006
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An asshead, a person who is hollow.
You are such a friggin tube, it hurts me.
by Pino March 31, 2003
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Another word for person that is cute and/or a nerd.
"You are a huge tube!"

by skd2488 October 22, 2007
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A water-pipe commonly referred to as a bong.
Often used by customers in glass shops because many shops are forced to not sell "bongs."

Tommy Chong associated the word "bong" with marijuana, so this has resulted in legal issues in some states. Tube was adopted as a more bong-like and shorter term than water-pipe.
"Let's rip tubes after class."

"Hey buddy, what are you looking for today?"- headshop employee
"A $300 bong"-customer
"You can't call it that. We don't sell bongs, only tubes/water-pipes."- employee
by truthin February 6, 2011
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noun. Scottish. short for tube steak. a tube steak is penis on account of it being cylindrical in nature and made of meat.
used to refer to someone being a dick.
"So your boyfriend's a Hearts supporter? He must be a total tube steak."
by peebles76 August 20, 2009
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