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tube on the right, as seen from the rear. Checking the preamp tubes in a tube tester is almost useless.
The best procedure is to substitute a tube that's known to be good and non-noisy for each tube in your
amplifier, one-at-a-time. Here are general guidelines. If the problem appears only in the Lead mode, then
the culprit is Vl, furthest to the right, but may also be in V2 or V3. If the problem is in the Rhythm mode
only, then V2 is usually the problem (V2 is second from the right, seen from the rear). Sometimes it also
can be V3. If the Reverb is noisy or has a problem, replace V4.
Sometimes the insides of the power tubes themselves can be heard rattling. If the power is weak and
your tone is flat, try replacing the larger power tubes, type EL84, also known as 6BQ5. We strongly
recommend you use only genuine MESA tubes. (Your amplifier guarantee is valid only when all the
tubes are MESA brand or come from us.) Power output tubes are like guitar strings; they begin to
deteriorate as soon as they're put into use. You may notice improved performance by replacing your
EL-84's every few months. But do not change the 12AX7 tubes unless a specific problem comes up.
Their aging is very slow and you won't likely hear any improvement by changing them unless one has
become noticeably noisy.
Your combo-type amplifier is equipped with a special tube clamping plate for protection against vibration
as well as from flying footswitches and other debris which might be stashed in the back. To gain access
to the tubes, merely release the barbed nylon catches and the aluminum plate will fold down on
concealed hinges. Changing 12AX7 preamp tubes is easier if you first remove one or two of the larger
power tubes. Make certain you have all the tube pins aligned properly before pushing them in.
If your amp is fitted with an EWM speaker, you my need to remove the four mounting screws on the top
of the cabinet and slide the chassis back before gaining enough access to change a 12AX7.
After rough handling of the amplifier or when replacing tubes, make certain they are plugged all the way
into their sockets and are centered within the metal holes of the chassis sheet metal. A tube that is
leaned over in its socket can vibrate and buzz against the metal chassis, causing annoying noises. Note:
A power tube that is crooked can also reduce clean volume levels dramatically, and cause break-up
similar to a bad speaker. Should this sound occur, insure that your power tubes are seated squarely in
their sockets.
ENJOY Most of all… enjoy your .50 Caliber Boogie. It's really a great sounding amplifier and it's been
built to satisfy professional demands for performance and reliability. And it should last a lifetime with only
moderate care and maintenance. It is extremely user-friendly and there's almost nothing you can do to
damage it, short of accident or obvious abuse. We've put our most into the design of the .50 Caliber so
can get the most out of your playing. We've consciously made it feel "real spongy" so it helps your
playing... even smoothes over your little mistakes! (Or as one good player said, "It makes my sloppiness
sound like expressiveness… I love it!")
We're still a small, personable company of (mostly) musicians and we always like hearing from other
musicians and Boogie owners... so drop us a card sometime. And remember: The essence of music is
the PLAYING! So grab your guitar and GO FOR THE GUSTO!
Very Best Wishes
MESA/Boogie Ltd.
Randall Smith
Designer & President
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