In guitar amplification, a tube is considered "mature" when it has moved past its initial burn-in phase but remains well away from the end of its operational lifespan.
: The definitive American tone (Fender style). Mature 6L6 tubes are celebrated on TGP for tight, deep bass response and sparkling, glass-like top end. The TGP Holy Grail: Vintage NOS vs. Modern Production tgp mature tube