A lost Dumble Overdrive Special that's been called “possibly the greatest amplifier ever made“ has resurfaced after 40 years

That electric guitar ace Jason Isbell is a vintage gear connoisseur is no state secret.

Just last week, he used both a blackguard, ‘50s-era Fender Telecaster and a 1961 Gibson SG during an onstage jam with Pearl Jam's Mike McCready. Oh, and did we mention that McCready used Isbell's pristine 1960 Strat for that performance?

Of course, Isbell is also the owner of “Red Eye,” the legendary 1959 Gibson Les Paul that once belonged to late Lynyrd Skynyrd guitarist Ed King.

The latest addition to Isbell's venerable gear collection, though, might just be the most impressive yet.

The item in question is a Dumble Overdrive Special guitar amp – serial number 22. Originally made for Dennis Herring – a producer and guitarist best-known for his work with the likes of Bonnie Raitt and Buddy Guy – the amp was never documented, and was only unearthed this year.

You can hear the amp – which Isbell has described as “possibly the greatest amplifier ever made“ – in action, via guitarist Gabriel Bergman and Vertex Effects owner/CEO Mason Marangella, below.

For those in need of a quick refresher, Dumble amps were hand-built – one-by-one, and uniquely tailored to each guitarist and their playing style – by the late Howard Alexander Dumble. Virtually unrivaled in their reputation, Dumbles have taken pride of place in the rigs of John Mayer, Slash, Kenny Wayne Shepherd, Stevie Ray Vaughan, and countless other guitar heroes, and typically command eye-watering prices when they appear on the secondary market.

In any case, even among the storied ranks of Dumbles, Overdrive Special no. 22 is a special beast. Indeed, Marangella says that – though he's played through several Dumbles over the years – “none of them come close to this one.“

For their demo, Bergman uses a 2012 '59 reissue Les Paul, a Strat, and a Tele-style model, with a fairly minimal pedalboard consisting of a Strymon Timeline, TC Electronic Hall of Fame mini reverb pedal, Ceriatone Kleinulator effects loop buffer pedal, and a Vertex Boost, which noted Dumble aficionado and guitar virtuoso Robben Ford has described as one of the few pedals that works well into the front of an Overdrive Special.

Isbell only acquired Dumble OS 22 after he recorded his new album, Weathervanes, but it has since been incorporated into his live rig.

You can hear it in action with Isbell and his band, the 400 Unit, in the live clip below.