The MESA 5AR4 Rectifier Tube produces a vintage feel with light to mild "sag". While it produces more "sag" than Silicon Diodes, it is the least "saggy" of MESA's tube rectifiers; great when you need a fast response. 5AR4 is used in vintage MESA amps like the Heartbreaker, Blue Angel and Maverick as well as many other vintage, non-MESA amplifiers. MESA Rectifier Tubes are premium grade and offer unsurpassed consistency and reliability for ANY tube amplifier, and certainly MESA amplifiers!