Koch Classictone Bedienungsanleitung Seite 7

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, FIRST REMOVE THE CE
SAFETY CAP.
•
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 with the same type and bias-class number are used
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 amp's best performance. Tubes behave like strings, they loose
highs, lows and dynamics and after a period of time they have to be changed.
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 (ECC83/12AX7A, 7025/12AX7WA):
- 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:
- Loud crackling that is not affected by front panel controls.
- Intermittent or regular blowing HT fuses.
- Weird amp 'distorting' and/or hum
Changing a tube is a simple and quick fix for most problems in your amp.
In case of failure, just one or both POWER TUBES can be replaced without
rebiasing only if KOCH tubes with the SAME TYPE AND BIAS-CLASS
NUMBER are used.
If EL34's with a different or unknown bias-class number are used for
replacement, BOTH TUBES have to be replaced and the amp has to be
REBIASED.
Please always use two matched EL34 (= one duet) replacement tubes to
obtain the amps best performance.
Again, if you have any doubts, please take no risks and consult your
dealer and/or a qualified technician.