Electro Harmonix 6550EH Vaakumtoru

Built for the punishing end of the amp

Electro-Harmonix designed the 6550 for the most demanding environment a power tube meets: high-powered bass amplifiers such as the Ampeg SVT, where output tubes run hot for hours. It is a high-power octal beam tetrode rated at 42 W plate dissipation, and it works in any amplifier specified for either the 6550 or the KT88.

Headroom is the point

For bass players the practical benefit is headroom. A tube that runs out of steam compresses the signal and flattens the instrument's dynamics; one with reserve lets the full dynamic and tonal range of the bass through, from a light touch to a hard dig. Nickel steel side rod mica supports hold the internal structure steady, so the tone stays consistent even in a combo where the tube sits inches from the speaker and takes constant vibration.

Before you fit it

The 6550 uses an octal base. Output tubes work as a set, so replace all of the output positions together and have the amplifier re-biased — this is a power tube and correct bias is what keeps it, and the amp, alive. This item is a single tube.