central preamp tubes. We strongly recommend you use only genuine MESA tubes. Other tubes- including Groove Tubes - often aren't
good enough. YOUR AMPLIFIER'S WARRANTY IS ONLY EFFECTIVE WHEN USING ALL GENUINE MESA TUBES.
POWER TUBES
The big power tubes are like the strings on your guitar: they begin to wear down as soon as you play them. Severely run-down power
tubes sound flat, dull and listless... just like worn strings. If you play regularly, you should plan on replacing power tubes every 8 to 12
months. Power tubes only rarely fail, but here are some of their symptoms: Loud crackling that is unaffected by front panel control
settings (often you can see sparks inside the bad tube, so just replace it). Intermittent or regular blowing of fuses is usually caused by a
bad power tube. And again, the problem is very often visible because the whole internal plate structure of the tube will glow red hot, the
amp will distort, lose power and hum. If this happens try to spot the bad tube then turn the amp to Standby as quickly as possible. Quite
often a tube will suffer a temporary "space charge short" as described; then, when switched off and on again it will work properly. This
can get you through the gig but identifying and replacing the bad tube will insure reliability.
In an amp with four power tubes, the shorted tube will cause the one next to it to also turn red hot even though that tube is fine. You
can determine which tube is actually bad by using the 60/100 or Class A switch to turn off two of the four tubes (it turns off the center
two tubes). And you can safely run the Boogie with only two of the four tubes plugged in. In this manner you can at least determine
which pair ("outer" or "inner") contains the defective tube, and then you can isolate the defective by substituting a replacement for each
of the two "suspects", one at a time. In the 100-watt (non-Simul) mode, the same tube (6L6) is used in all four sockets, so a good tube
from the inner pair could be used to replace a defective in the outer pair if necessary; but in the Simul-Class model, the inner tubes
must be 6L6's while the outer tubes must be EL-34's.
When removing a power tube, first bend the retaining ring out of the way. Then GENTLY rock the tube back and forth slightly, while
pulling down. If you rock it too far, you will break off the plastic key on the tube base. This is not something we cover under warranty. If
you're reasonably careful, you won't break it. If it does break off, you can still use the tube as long as it's oriented properly in the socket.
Look carefully at the bottom of the tube and you'll probably see the outline of the plastic key. This should line up with the notch in the
center hole of the tube socket. Also look for the scratches in the plastic base caused by the retaining ring. When you think you've got it
right, make sure the amp is on Standby, then turn on the Power. If the tube filament lights, up, then you've got it right and everything is
OK. If the tube doesn't light up, turn off the power and try again to get the tube plugged in properly. A broken plastic key does not hurt
the working of the tube, it just means it can be plugged in seven wrong ways and one right way. By double checking the filament -- with
the amp on Standby -- you can be absolutely certain that everything is OK without any risk of damaging your amplifier.
NOTE: Series 300 amplifiers with Simul-Class have a different tube layout than the regular 75-watt Simuls. In the Series 300 Simuls,
the EL34/Class A sockets are the middle pair of sockets - that is, the 3rd and 4th sockets as you count across. The other sockets (1&2
and 5&6) use 6L6's.
BIAS
Most amplifiers have a "bias adjustment" which must be set right for correct operation of the power tubes. But these variable bias
supplies can wander out of adjustment, and there is often confusion about the correct setting anyway. To avoid these potential
problems (and save you the technician's fee) each Boogie's bias supply is built with parts selected for that exact amplifier and there is
nothing to adjust. So when it comes time to replace the power tubes (after 6 to 12 months of vigorous use) just POP in a set of genuine
MESA replacement tubes making sure the black spring clamps are snug against the tube base. We hear of many problems caused by
using other brands, so: Preserve your amp's warranty -- use only genuine MESA replacement tubes.
CALLING IN TO BOOGIE
Can you call Marshall? Roland? Peavey? Fender? No. But you can call MESA/Boogie. We back you up and we back our equipment
up. We want you to be totally knocked-out with your Boogie's performance and we're glad to help keep it that way. All we ask is that
use moderation and good judgement in calling us. Please run through this list of user maintainable operations before calling us or a
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