Koch Studiotone XL - Handbuch (Seite 6)

[8] SPEAKER OUTPUT JACKS: Provided for
connection of speaker(s) or speaker cabinet(s) with a
minimum total impedance of 4, 8 or 16 ohms. These
output jacks can NOT be used to connect multiple
cabinets, one at each output, you can only use one
output at the time.
If a separate speaker cabinet is used, always
use speaker cable.
[9] SPEAKER ON/OFF SWITCH: This switch
disconnects the output of the amp from all three
Speaker Ouptut jacks and loads it with an internal 25W
dummy load. This allows you to play the amp at full
power without hearing anything while using the outputs
[5] [6] [7] for recording or other purposes.
WARNING: Never play the STUDIOTONE-XL
without a speaker connected if the Speaker On/Off
switch [9] is in the “On” position. This may cause
serious damage to either the power tubes and/or
the output transformer.
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: The STUDIOTONE-XL has an auto-bias circuit
so it does not have to be rebiased after replacing the
EL84 power tubes.
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 amps best
performance. Tubes behave like strings, they lose 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, 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 (EL84):
- 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 both POWER TUBES can be
replaced without rebiasing.
Please always use four matched EL84 (= one
quartet) 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.