Collection: Vacuum Tubes 73 73 products

Preamp, power and rectifier tubes

Preamp tubes such as the 12AX7 (ECC83), 12AT7 and 12AU7 amplify the small signal from your instrument and shape gain and tone. Power tubes such as EL84, EL34, 6V6, 6L6 and KT88 drive the speaker and decide much of an amp's headroom and character. Some amps also use a rectifier tube, which converts AC to DC for the amp's power supply and affects how the amp responds when played hard.

Matching and biasing

Power tubes in push-pull amps are often sold as matched pairs or quads, so they draw similar current and work in balance. Fixed-bias amps need their bias checked when power tubes are changed, while cathode-biased amps adjust themselves. Preamp tubes need no biasing and are the easiest to swap.

When to replace

Tubes wear gradually. Signs include loss of volume or sparkle, extra hiss or hum, crackling, and microphonic ringing when you tap the amp. A power tube that glows bright red on its plates or a blowing fuse are reasons to switch off and have the amp checked straight away.

Safety and tone

Valve amps hold lethal voltages inside, even after they are unplugged. Swapping a preamp tube in a socket you can reach is routine for many players, but internal work and biasing belong with a qualified technician. Swapping a preamp tube for a lower-gain type is a common way to get more clean headroom.