Korpa 
A medium-output power tube (generally 20-25 watts) often used in Fender® professional amplifiers including the Bassman®, Bandmaster®, Concert, Dual Showman®, Hot Rod™ Series, Pro Series, Super Reverb®, Tremolux™, Twin, Vibrolux®, Super-Sonic™, Blues Deluxe™, Blues DeVille™ and others. Available in many variations, its response is round, with a pronounced midrange character; strident and chesty with a super-bright and clean, powerful punch. Perhaps the most recognized signature tone for U.S. guitar music of all styles from the ’60s onward.
Solid and consistent performance; very sturdy and reliable. AKA 5881.
Matched quartets of 6L6-R tubes rated from power range 1-10. Each quartet has a specific rating (i.e. R2, R7, etc.) and is matched and biased to a specific output level.
R1-R3 = Low:
- Early distortion, wide range, softer attack good for Rock and Blues solos.
R4-R7 = Medium:
- Normal performance, great dynamic range/attack and best all around rating type for all styles of playing
R8-R10 = High:
- Most dynamic range, most clean power/less break-up for power players, Jazz and bass amps.
