Koch Multitone Bedienungsanleitung Seite 7

POWER TUBE OPTIONS
Each type of power tube has its own distinctive sound character, therefore
changing to a different type (or mix of types) of power tubes will also change
the MULTITONE's overall sound.
50W VERSION
The 50 Watts version of the MULTITONE accepts either 2xEL34 or 4x6V6.
100W VERSION
Due to special bias control circuitry, the 100 Watts version of the MULTITONE
is able to accept almost any type of power tube, for example: EL34, 6CA7, 6L6,
6550, KT66, KT77, KT88, KT90, KT100.
The MULTITONE-100 is provided with two seperate bias control trimmers
(located inside on the PC board), one for the two inner power tubes and one for
the two outer power tubes, therefore either one quartet (=4 matched tubes) or
two duets (= 2 matched tubes) of power tubes can be used. For example the
two outer tubes may be EL34's while the two inner tubes are 6L6's or 6550's.
REPLACING TUBES
•
SAFETY FIRST: DISCONNECT THE POWER CORD FROM ITS POWER
SOURCE AND LET HOT TUBES COOL.
•
CHECK THE 'TUBE LOCATION DIAGRAM' ON THE CHASSIS FOR THE
CORRECT TYPE NUMBERS AND LOCATIONS.
•
REPLACE TUBES ONLY WITH ORIGINAL KOCH HIGH QUALITY
TUBES. (IF OTHER TUBES ARE USED THE WARRANTEE OBLIGATION
EXPIRES)
•
BEFORE REPLACING THE POWER TUBES, REMOVE THE CE SAFETY
CAP FIRST.
•
AFTER REPLACING THE POWER TUBES, PUT THE CE SAFETY CAP
BACK IN PLACE.
NOTE: Always have the amp rebiased after replacing the power tubes. Biasing
instructions can be found inside the amp. Rebiasing the amp is not neccessary
only if KOCH power tubes are used with the same type and bias-class number.
If you have any doubts, please take no risks and let a qualified technician
do the job.
Preamp and Power tubes wear out and have to be changed from time to time to
maintain the MULTITONE's best performance. Tubes behave like strings, they
lose highs, lows and dynamics and after a period of time they have to be
replaced. Exactly when is hard to say but this is an indication: if you play almost
every day change tubes each year, if you play once or twice a week change
tubes every 2-3 years.
Tubes rarely fail. If they are bad, these might be the symptoms:
PREAMP TUBES (ECC83, 12AX7, 7025):
- Microphonic whistling or squealing on one or both channels.
- No or low amp volume on one or both channels.
- Excessive noise on one or both channels.
POWER TUBES (EL34, 6L6, 6550) :
- Loud crackling that is not affected by front panel controls.
- Intermittent or regular blowing fuses.
- Weird amp 'distorting'.
- Hum.
Changing a tube is a simple and quick fix for most problems in your amp.
In case of failure, just one bad power tube can be replaced without rebiasing,
only if a KOCH tube with the same type and bias-class number is used.
If power tubes with a different or unknown bias-class number are used for
replacement, the two inner and/or the two outer tubes have to be replaced and
the amp has to be rebiased.
Always use a set of four (one quartet), or two sets of two (two duets)
matched replacement power tube sets to maintain the amp's best
performance.
Again, if you have any doubts, please take no risks and consult your
dealer and/or a qualified technician.