A WORD ABOUT TUBES:
Vacuum tubes can only last so long. Allowing your amp to cool down before moving it will help prolong the life of the tubes. Even so, after about a year (or sooner if you're on tour or jammin' more frequently than most) you may notice the output of your amp just isn't as "alive" as it used to be. If the sound from your amplifier starts to grow weak, lacks punch, fades up and down, loses highs and lows, gets "funny" (clanking sounds, etc.), it's very likely that the power tubes are worn out and need replacing. Since power tubes work together in an amplifier, it is important that they all be replaced at the same time with a matched set of tubes.
If you're looking to change the sound of your amp, you can replace the stock 6L6 power tubes with EL34's. 6L6 tubes tend to give you more of the "American" sound, with lots of solid power, even up to their full output, with a lot of dynamic headroom. EL34 tubes tend to give you that "English/British" sound: they distort sooner and provide a more controllable and less penetrating distortion effect when overdriven. Either way, your amplifier has been engineered to facilitate power tube replacement, with automatic bias- ing when changing tube types. IF YOU DON'T CONSIDER YOURSELF ADEPT WITH A SCREWDRIV- ER, REFER POWER TUBE REPLACEMENT TO A QUALIFIED SERVICE CENTER. Otherwise, unplug your amp, allow it to cool for at least thirty minutes, and proceed as follows:
•Turn the amp so you're looking at its rear panel.
•Unscrew and remove the wooden rear cover.
•Remove the power tubes one at a time by slightly spreading the wire tube clamps with one hand and gently pulling the tube out of the socket with the other hand.
•When inserting new power tubes, carefully align the tab in the tube's plastic base with the slot in the socket and press the tube gently but firmly into place.
•Replace the rear cover piece and tighten the screws. (Avoid overtightening.)
•Power up the amplifier and let it sit for at least twenty minutes before playing.
If the amp starts to squeal, gets noisy, loses gain or starts to hum, the preamp tubes may be bad.
Since removal of the tubes may expose extremely hazardous voltage levels, always refer replace- ment of the preamp tubes to a qualified service center. Insist upon using only the highest quality, low- microphonic tubes!
SYSTEM BLOCK DIAGRAM:
Speakon® is a registered trademark of Neutrik USA
7