In an electronic device, glass vacuum tubes, also called thermionic valves, amplify a signal by controlling the movement of electrons in a controlled, low pressure space. Preamp tubes overdrive the signal and add distortion to the signal.
Use
Preamp tubes are used in the gain stage of an amplifier. A preamp boosts the signal before it reaches the power stage of the amp.
Distortion
Preamp tubes that are pushed hard with on overdriven signal add upper layer harmonics to the signal, which imparts a characteristic warmth and richness to the overall sound. This warmth is considered appealing to the the human ear and it is used to create distortion in guitar amps and effects and the complex sound qualities found in professional recording equipment.
12AX7
The 12AX7 is the most common preamp tube used in amplifiers and signal processing equipment. It has the highest amount of gain when compared to other preamp tubes of similar types.
Other types
12AT7 tubes usually impart a brighter, slightly cleaner sound than 12AX7 tubes. 12AU7 tubes have a much cleaner sound and are often used in high fidelity sound equipment.
Applications
Preamp tubes are used in guitar amplifiers, microphone preamps and other signal processing devices such as recording studio compressors and equalizers.
Tags: Preamp tubes, cleaner sound, Preamp tubes used, signal processing, tubes used