Vacuum tube
A vacuum tube is an electronic device that amplifies signals by use of charged metal plates sealed inside an airless space. Typically the outer housing is made from glass.
Vacuum tubes used to be very widely used, but have been almost entirely replaced by transistors. Small pockets of use have continued:
- Military - Some radar and communications equipment
- Broadcasting - Sometimes better than transister equivalent
- Music - Widely used in guitar and bass amplifiers. Considered to have a more musical sound with natural-sounding distortion and pleasant overtones.
Glossary[edit]
- Clean - The ability to amplify a signal without adding overtones or distortion
- Compression - Running up against the limits of amplification, loud sounds cannot get any louder but quiet sounds continue to be amplified. Makes picking and finger movements sound more prominent.
- Distortion - Clipping of signal or creation of overtones due to a tube being asked to do more than it can handle
- Function stage - Place for tubes within more sophisticated amps that is involved in signal processing but niether pre nor power amp.
- Gain - Increase in the amplitude of the voltage swing in the signal. Typical instrument level is 1/10 volt, but by the time the signal exits the preamp section it might be 5 volts.
- Harmonics - reproductions of the notes octaves higher than the original signal
- Microphonics - Problem with tubes where positive feedback causes a squealing sound
- Overtones - Sounds added to the instrument signal by the amplifier
- Pre amp - First section of the amp, takes the instrument signal and does most of the tone-shaping.
- Power amp - Last section of the amp, takes the pre-amp signal and makes it strong enough to drive the speaker.
- V1 - First tube in the amp. Closest to the instrument. Has the most influence on the tone generated.
Common types[edit]
There are thousands of types of vacuum tubes but most have been discontinued. The following are still widely used.