Guitar greats Hetfield and Hammett Metallica reflect on their first encounter with Mesa/Boogie's Mark I guitar amp.
The event will return to London’s Underglobe, beneath Shakespeare’s Globe Theatre, on 12 September.
Def Leppard, Tool and Slipknot were previously announced as the 2019 event's headlining acts.
The prog-metal supergoup feature former Dream Theater mainstay Mike Portnoy and ex-Guns N'Roses guitarist Ron 'Bumblefoot' Thal.
The 40th anniversary album celebrations of the Rush catalogue continue with 1 December 2017's expanded, multi-format edition of A Farewell To Kings.