Ruby, distributed by California-based Magic Parts LLC, is a brand of vacuum tubes aimed at guitar and bass amplifiers. Magic Parts was founded in 1984 by Thomas McNeil, and the Ruby line has since become a fixture at repair shops and retailers for players retubing combos and heads. Rather than operating its own glass factory, the company sources tubes from manufacturers in countries including Slovakia and China, then tests, burns in, and matches them in the United States before resale.

The catalog spans the common preamp types — 12AX7/ECC83, 12AT7/ECC81, 12AU7/ECC82, EF86 — and power tubes such as 6L6, EL34, EL84, 6V6, 5881, KT66, KT88, 6550, and 300B, alongside rectifiers like the 5AR4/GZ34 and 5U4. Ruby also packages amp-specific retube kits for popular models from makers such as Fender, Vox, Mesa Boogie, and Supro, and sells adjacent amp parts including transformers, reverb tanks, and chassis hardware.

The brand's reputation rests on its matching and grading process: tubes are evaluated for plate current, transconductance, microphonics, and mechanical noise, and sold with a six-month warranty. That service-oriented approach has made Ruby a common OEM and replacement choice for amp techs rather than a boutique or NOS specialty label.

Ruby has 6 products cataloged on Equipboard, including Guitar Amplifier Tubes, Virtual Instrument, and Reverb Effects Pedals. Their gear is featured by 1 artist, with the strongest followings in Rock. Notable users include Dick Dale.