Genalex is a vacuum tube brand with roots in the British firm Marconi-Osram Valve Co., whose premium Gold Lion line powered a generation of iconic hi-fi and guitar amplifiers from the late 1950s through the 1970s. The original KT88, introduced in 1957, became a defining power tube in designs like the Dynaco Mark III, McIntosh MC275, and Marshall Major, and earned a reputation as the "King of Power Tubes." Genalex ceased production in the early 1980s, and surviving original-era tubes have become collector items.

The brand was revived by New Sensor Corporation, the company behind Electro-Harmonix, which reissues Genalex Gold Lion tubes at the Reflektor factory in Saratov, Russia. The reissue catalog includes power tubes such as the KT88, KT77, KT66, and 300B; preamp tubes including the ECC81 (12AT7), ECC82 (12AU7), ECC83 (12AX7), and E88CC (6922); and the GZ34 rectifier. The tubes are marketed as hand-assembled recreations of the originals, with features like gold-plated grid wire and tri-alloy clad plate structures.

Genalex Gold Lion tubes are widely used in boutique and high-end guitar amplifiers as well as audiophile tube gear, and they are sold through specialty retailers such as The Tube Store, Tube Depot, Amplified Parts, and Upscale Audio, alongside Electro-Harmonix's direct shop.

Genalex has 2 products cataloged on Equipboard, including Guitar Amplifier Tubes. Their gear is featured by 1 artist, with the strongest followings in Rock and Blues. Notable users include Andy Martin.