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PAGE 6
SPEAKER OUTPUTS: (Continued)
NOTE:
If you opt to use only one channel of the
2:100
with speakers connected to that
channel’s output only, you must turn the unused channel’s level control to zero! Otherwise the channel will be operating without
a load, and damage to the tubes and/or the transformer will result.
TUBE BAY:
The power tubes used in the
2:100
are
MESA/Boogie
STR-430 type 6L6 GC’s. These tubes have been tested in
the amplifier during several “burn-in” periods before leaving the factory. You can expect 6 months to 2 years (or more) of outstanding
performance from your
MESA/Boogie
power tubes, depending on use. Tube wear is gradual and usually goes unnoticed until new
replacements are installed. Worn power tubes tend to sound flat with reduced punch, clarity and high end. Occasional loss of power
or sporadic blowing of fuses is nearly always caused by
troublesome power tubes.
Often, you can spot the tube at fault and replace it alone, at
considerable savings over replacing all the output tubes. A
tube that arcs or “flashes over” inside should be replaced
immediately. (In an emergency, you can just remove the
bad tube and go on with the show...”running on 3 cylin-
ders.”) Sometimes a tube will “short out” intermittently, turn-
ing red-hot all over the large metal plate inside. But usually
a momentary switching off of the STANDBY or POWER Switch will enable the tube to straighten out its electron flow and return to
proper operation. Should this happen repeatedly, careful observation will usually reveal which tube is shorting, even though one or
two others may also turn red-hot after a few moments.
By viewing the tubes, try to verify which one is reddest or turns red first - that is the bad one and the others are most likely unharmed.
Internal circuitry is built to withstand tube failure as much as possible; even if damage were to occur, it would be minor and easily
repairable.
When replacing tubes, please use only the
MESA/Boogie
types specified. Using other tube brands and/or types will invalidate your
amplifier’s warranty! To remove tubes, you must first push back the spring retainers clamped against the tube base. When re-installing
power tubes, check that the spring clamps are making good contact with the tube base; bend them in toward the center before
plugging in the tube, if necessary. Avoid excessive wiggling of the tubes when removing or installing them, as it can break off the small
plastic key which insures correct orientation of the tube in the socket. Make sure you check out the sections on Power Tube and Pre-
Amp Tube maintenance located further back in this manual. Some helpful tips on prolonging the life of your amplifiers’ tubes makes
these maintenance sections worthwhile reading.
DRIVER TUBES: 3 x 12AX7A
The three small tubes are type 12AX7A, also known as 7025 or ECC83. These tubes are very
long lasting and trouble free in the
2:100
; should they ever need replacement due to a specific malfunction, genuine
MESA
replace-
ments are recommended for best performance.
NOTE:
You must remove the top cover of the chassis in order to gain access to the driver
tubes. These tubes can become quite warm. Allow them to cool down before changing and its
always a good idea to power down the unit when changing any of the tubes.
Also, be aware that some of the circuitry components (namely the large round capaci-
tors running parallel to the three driver tubes) will store a substantial amount of elec-
trical charge even after the amplifier is powered down. For safety reasons be sure
REAR PANEL
(Continued)
MESA
MESA
12AX7
12AX7
MESA
MESA
12AX7
12AX7
MESA
12AX7
GENTLY ROCK TUBE BACK AND FORTH WHILE
PULLING UPWARD CAREFULLY
MESA/Boogie type STR 430 - 8 x 6L6
COOLING FAN
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