Hughes & Kettner Duotone Head Guide Rapide page 10

Duotone™ Head
player, etc.) for rehearsals or practice sessions. If you choose to use the
FX RETURN this way, use the FX-LEVEL knob to determine the balance
of levels between your guitar's signal and the connected signal source.
5
Replacing Tubes, Maintenance & Care
The Duotone™ ships with EL34 and 12AX7 tubes by RUBY®. Once
they've been burned in (initial continuous operation under a load),
these undergo an in-depth selection process where their electrical
values and mechanical status (microphonics) are checked. Beyond that,
they're installed in a finished amp and their sound is auditioned in a
listening benchtest. One of the most important steps is Power tube
matching, a process whereby tubes with the same characteristics are
selected and combined to make matched sets.
When is it a good idea to replace tubes?
The tubes in the Duotone™ are exemplary in terms of quality,
workmanship and long service life. If you nevertheless come across
a problem, please be sure to run down the following checklist before
you swap out your old tubes for new ones:
Was the fault or failure of the Power tube caused by the tube itself or
a flawed peripheral device or component, perhaps a defective speaker
cable? (If you don't get to the bottom of the problem and remedy it, it
may crop up aGain even after you replace the tubes.)
Did the mains voltage fluctuate or spike while the amp was on? In
all-tube amps, over-voltage surges in the mains net can certainly blow
fuses or even the amps. Over-voltages are often caused by generators
or improperly installed high-current Power circuits.
Did a fuse blow even though none of the tubes is actually defective?
An old fuse, tube de-ionization or mains voltage Power surges could
conceivably have caused it to blow. In this case, replacing tubes of
course is a waste of money and time.
Tubes definitely show signs of wear when their service life is coming to
an end, such as increased microphonics, noise, muddier tone through
loss of high-end frequencies, degraded performance, etc. You should
take these indications seriously and replace old tubes because not only
do these side effects take their toll on sound quality, they also indicate
the affected tube is about to fail.
NOTE: Although it may be tempting to find out what an amp sounds
like with different tubes, we urgently recommend that you refrain from
replacing tubes for experimentation purposes. Handled improperly,
this will damage the amp and lead to incredibly steep repair costs.
What should you keep in mind when you're
replacing tubes?
The golden rule: Replacing tubes is a job best left to qualified
professionals. Accordingly, these guidelines are addressed to
reputable technicians who earn their living with a screwdriver: Pull
the mains plug of the Duotone™ and allow for a discharge time of at
10
least two minutes before removing the sheet metal panel on the rear
of the amp. Once the panel is off, you can cautiously ease the tubes
out of their sockets. A single Power tube may only be replaced if the
replacement tube is precisely matched to the original, in other words,
it has the same characteristics. As a rule, if you are replacing Power
tubes, use matched sets only.
If you're installing a new set of Power tubes with characteristics
identical to the old set, it is not absolutely necessary to re-bias the
amp. If, on the other hand, you install a new set with characteristics
that deviate from the old set, you definitely should re-bias the amp.
AGain, biasing an amp is not a DIY task. It takes experience and a
extensive working knowledge in measuring techniques, which is why
this job should be carried out exclusively by qualified technicians with
tube amp tuning experience.
How can you extend the service life of tubes?
Never operate the Duotone™ without connecting a load (loudspeaker)!
With this in mind, you should always use high-quality, heavy-duty
speaker cables that won't crimp or snap.
Use the STAND BY switch! Warming tubes up unnecessarily wears
them out that much quicker. Make a habit of shutting down the anode
voltage via the Standby function and you'll enjoy many more hours of
operation.
Avoid exposing the amp to vibrations, especially when it's Powered
up. Switch the amp off a good while before moving the amp so that
the tubes can cool off completely first.
Proper biasing and trimming extend service life. Whenever you feel
that tube wear is on the rise, be sure to have a technician check the
amp's bias and trim settings.
!
Here are a few more basic rules that will extend the service life
of your amp enormously if you follow them:
•
Make sure all peripheral devices and connecting cables are in a state
of good repair! - Ensure plenty of air can circulate around the amp's
ventilation slots at all times - your Duotone™'s life depends on it.
•
Definitely avoid exposure to mechanical shocks and extreme heat,
dust and particularly moisture.
•
Be 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 Duotone™ 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.
•
Be sure the AC Power source delivers the current that your amp is
designed to handle before you plug it in. When in doubt about the
local rating, ask the venue's sound technician or a stage hand.
•
Refrain from DIY repairs! To be on the safe side, you should also
have a qualified technician replace internal fuses.