Mesa/Boogie Rectifier Stereo owner manual Troublesome power tubes

MESA/Boogie type STR 430 - 8 x 6L6

FUSE ESUF

REAR PANEL (Continued)

SPEAKER OUTPUTS: (Continued) NOTE: If you opt to use only one channel of the 2:100 with speakers connected to that channelÕs 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 GCÕs. These tubes have been tested in the amplifier during several Òburn-inÓ 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 Òflashes overÓ inside should be replaced immediately. (In an emergency, you can just remove the bad tube and go on with the show...Órunning on 3 cylin-

ders.Ó) Sometimes a tube will Òshort outÓ 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 amplifierÕs 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 amplifiersÕ 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.

MESA	MESA	MESA
12AX7	12AX7	12AX7

GENTLY ROCK TUBE BACK AND FORTH WHILE

PULLING UPWARD CAREFULLY

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

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