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7. Tube Installation and Replacement
Tube Quality
Currently manufactured tubes are built in China, Russia, and the Czech Republic, and are not
built to the same quality standards as tubes manufactures by the U.S. manufacturers in the
“glory days” of tube manufacturing.
We musicians choose to use to vacuum tubes because of their tonal qualities, but we need to
accept that the tubes available to us these days can be imperfect devices and are most certainly
the least reliable component in the entire amplifier. Tubes made these days can fail at any time,
even after only a few hours of use. They are quite sensitive to mechanical shock and can fail as
a result of the amplifier being dropped sharply as happens often in shipping.
Aside from simply failing outright (causing the amplifier to produce no sound), tube defects can
create a number of different noises (such as crackling, hissing, humming, etc.) and these noises
can occur either continuously, intermittently, or in response to your playing (e.g. a crackling or
other type of noise which occurs only when you hit a note).
Tube defects/failures are the number one cause of problems with any tube amplifier. If you
experience a problem with your amplifier, the first step in debugging involves consideration of
the possibility of a tube problem.
I subject all tubes to a thorough burn-in and test procedure to ensure that they are up to spec
and operating perfectly. However, it should be known that the majority of tube failures occur
early in their life and may occur as a result of the jostling and jarring that an amp can receive in
shipping. In spite of these efforts to ensure tube quality, early-life tube problems are often not
detectable by any form of testing.
Tube Installation
To replace the preamp tubes of your amplifier, you must first remove the metal shield covering
the tube. This is done by pressing the shield toward the chassis and turning it counter-clockwise
to release it. Once the shield is removed, the tube can be removed by grasping it and pulling it
straight out of the socket. You may need to rock the tube slightly from side to side to free it
from its socket.
To replace the output tubes or rectifier tube, you should hold back the “butterfly” tube clips
which grab the base of the tube, and pull the tube straight out, grasping it from the base. It may
be necessary to rock the tube slightly in its socket while pulling, but be sure to rock it only
slightly or you may break off the center post in the base of the tube.
