LEVEL A/B
These two pots control the volume level of each side or channel of the 2:90. Since there's only one Standby Switch on this unit they may also be useful as channel muting controls. NOTE: If only one speaker is to be used on one channel and no speaker load on the other, always turn the unused channel’s Level Control to zero. To prevent oscillation (motorboating) turn the Presence Control of that channel all the way up.
PRESENCE A/B
These controls "open up" the 2:90 producing brightness and sparkle for clean sounds at higher settings or sizzle and edge when set high for distortion sounds. At lower Presence settings you can darken and compress lead sounds making them warmer and fatter. Turning the presence controls to zero "chokes the brights" completely, making the 2:90 great for jazz clean sounds or round vocal lead work.
POWER/STANDBY
These two toggles located next to the Presence controls deliver A.C. Mains voltage and D.C. filament voltage. When powering up cold - always turn the power on first - wait 30 seconds - then turn the Standby on. This procedure reduces shock on cold tubes and prolongs tube life. Remembering to use the Standby on set breaks also prolongs tube life. NOTE: Power tube life varies depending on many factors i.e. how much you play, how long you play, how you treat your equipment etc. We've found that most discerning pro's who use their gear five to seven nights a week start noticing some tone loss somewhere around 8 months to a year. Some people, however, use the same set of power tubes for years with no complaints. We recommend changing your power tubes once a year if you play a lot. This way you're ensured of smooth operation and optimum tone. Always use MESA power tubes of matching color codes whenever possible. These are matched correctly and hammer tested, and actually cost less than the so called matched competitors in most cases. Also, it keeps your 2:90's warranty intact.
MAIN FUSE
The recessed grey fuse cap located above the Pilot light holds the 290's main fuse. Should this fuse blow, replace it with
5
