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The MULTITONE-50 accepts either 2xEL34 or 4x6V6.
100W VERSION
Due to special bias control circuitry the MULTITONE-100 accepts almost any
type of power tube for example: EL34, 6CA7, 6L6, 6550, KT66, KT77, KT88,
KT90, KT100. Also the MULTITONE-100 is provided with two seperate bias
control trimmers (on the PC board), one for the inner two power tubes and one
for the outer two power tubes, thus enabling the use of mixed sets of power
tubes (two + two). So for example the two outer tubes may be EL34's while the
two inner tubes are 6L6's or 6550's.
(see REPLACING TUBES)
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 PEPLACING 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.
Preamp and Power tubes wear out and have to be changed from time to time to
maintain the amps 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 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 or more POWER TUBES can be replaced without
rebiasing only if KOCH tubes with the SAME TYPE AND BIAS-CLASS NUMBER
are 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
simultaneously and the amp has to be REBIASED.
Please always use four or two + two (see above) matched replacement power
tubes to obtain the amps best performance.
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