Standard Setup/Cable Connections; Tubes, Maintenance And Care; Troubleshooting; Technical Specifications - Hughes & Kettner CUSTOM TUBE Serie Manual

PURETONE - MANUAL

2.0 STANDARD SETUP/CABLE CONNECTIONS

INPUT
3.0 REPLACING TUBES, MAINTENANCE AND CARE
The PURETONE ships with EL34 and 12AX7. 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 PURETONE 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.
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 PURETONE and allow for a discharge time of at
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.
NOTE: You may install new, matched power amp tubes into the
SPEAKERS
PURETONE without having to bias the amp anew. The new set may
even have characteristics that differ from those of the old set, just
make absolutely sure that the tubes are matched.
The Class A circuit ensures that the amp is biased automatically,
so to speak.
HOW CAN YOU EXTEND THE SERVICE LIFE OF TUBES?
Never operate the PURETONE 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.
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 PURETONE'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 con-
nect to your amp and always check out their specs before you
plug them in. Never connect speaker cabinets with an impe-
dance (ohm) rating lower than the PURETONE 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.

4.0 TROUBLESHOOTING

1) The PURETONE won't power up when you switch it on:
• It's not getting AC power. Check the mains cable to see if it is
connected properly!
• The mains fuse is defective. Replace the fuse with another fuse
of the same type. If this fuse also blows, be sure to talk to your
local Hughes & Kettner dealer.
2) The PURETONE is connected properly, but no sound is audible.
• One or several GAIN or MASTER controls are turned all the way
down. Dial in higher settings.
• A shorted external speaker cable caused one of the fuses to
blow. Have a qualified technician change the fuse (ensure the
replacement fuse bears the proper rating).
5.0 TECHNICAL SPECIFICATIONS P. 22/23
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