Replacing Tubes, Service And Maintenance - Hughes & Kettner Edition Tube 25th Anniversary Manual De Instrucciones

4
4.0 Replacing Tubes, Service
and Preventive Maintenance
Your Edition Tube features factory-equipped EL84
and 12AX7A tubes. They are first burned in and
then checked for their electrical and mechanical
properties (microphonics), selected and matched, and
then given a final audio and response test once they
have been installed in a E dition Tube. One of the
most important steps in the testing process is power
tube matching, i.e. selecting and pairing tubes with
identical characteristics.
When should you replace tubes?
The tubes in your Edition Tube are of exceptionally
high quality and will last extremely long. If you do
encounter a problem, first check whether one of the
following situations apply:
• I s the defect a problem caused by a faulty or worn-
out tube, or is there actually a peripheral problem,
for instance a defective speaker cable that caused
damage to the tube? If this is the case, unless you
correct the defect first, the problem will recur once
you have installed a new tube.
• D id the AC power supply fluctuate during
operation? Whereas digital equipment often
malfunctions when the power supply dips below a
minimum value, all-tube amps tend to malfunction
when the power level rises above a certain value.
Generators and faulty high-power circuits often
cause these power fluctuations.
• D id a fuse trip although there was no plausible
cause? Aging fuses, particle ionization in the tube
or spark-over due to power spikes may cause this
type of problem. In this case, replacing a tube will
not solve the problem.
• O ld tubes begin to show signs of wear after they
have been in operation for a very long time:
increased microphonics and noise, treble loss, weak
power output, muddy sound, etc. are all indicators
of pending tube failure. Power amp tubes wear
out faster than preamp tubes. If you encounter
these problems, replace the tubes. Not only do old
tubes sound bad, they also have a tendency to fail
altogether.
We recommend you refrain from exchanging tubes
solely for sound experimentation purposes. Improper
use runs the risk of damaging your amp and will not
be covered under warranty. Besides, we tested every
conceivable tube option and installed the tube types
that deliver the best possible performance.
Edition Tube 25 Anniversary
th
Keep the following in mind when you are ready to
replace tubes:
• W e recommend only qualified service personnel
replace tubes.
• B efore removing the chassis, ensure the mains cord
is unplugged from the wall socket! Wait at least 2
minutes for the amp to power down.
• I f you are replacing a power amp tube, ensure the
replacement tube bears identical specs.
• U se only matched pairs of power amp tubes.
• I f you install a matched pair of tubes bearing
precisely the same specs as the original tubes, the
amp does not have to be re-biased. Conversely, if
the specs are not identical, the amp must be biased.
Biasing is a complex procedure requiring special
tools and should only be executed by a qualified
amp technician.
How can you extend the life of your tubes?
• N ever operate the Edition Tube without a
proper load (speaker) connected to the output.
Switch the amp off and let the tubes cool down
before transport. A quality flight case is a good
investment and is only slightly more expensive than
a complete set of tubes.
• P roper bias and trim are essential. If you find
the tubes need to be replaced too often, consult a
qualified t echnician.
All other Edition Tube components do not require
m aintenance. Use a slightly dampened cloth for
all metal parts and the exterior surfaces. Avoid
exposure to m echanical shocks, extreme heat, dust
and moisture. Ensure the cooling vents are not
obstructed during o peration.
Here are a few more basic rules that will extend the
service life of your amp enormously if you follow
them:
M ake sure all peripheral devices and connecting
cables are in a state of good repair! - Ensure plenty
of air can c irculate around the amp's ventilation
slots at all times - your Edition Tube's life depends
on it.- Definitely avoid exposure to mechanical
shocks and extreme heat, dust and particularly
moisture.
B e very careful about the kind of peripheral devices
you connect to your amp and always check out
their specs before you plug them in. Never connect
speaker cabinets with an impedance (ohm) rating
lower than the Edition Tube is designed to handle.
Under no circumstances should you connect
devices with high output signal levels (e.g. power
amps) to your amp's input.