Koch Classic-SE - Handbuch (Seite 4)

REAR PANEL FUNCTIONS
[1] A.C. POWER:
INPUT: Power cord input. The CLASSIC-SE is
equipped with a worldwide power supply. Inside the
amp a mains selector switch can be set on one of
three voltages, 100, 115 or 230. Either of these
voltages will work worldwide with minor power
differences. The amp will work on either 50 or 60
hertz. After resetting the internal mains selector
switch make sure fuses are replaced with printed
ratings on rear of amp.
FUSE: Both fuse and spare fuse are located on the
sled of the fuseholder. Fuse sled can be removed
with a screwdriver. If the fuse should fail, it must be
replaced with the same type and value in order to
avoid damage to the amp and to prevent voiding
the warranty.
If the amp repeatedly blows fuses, check for a bad
power tube. If tube-failure is not the cause, the amp
should be taken to a qualified service center for
repair.
WARNING: Only a qualified technician should
attempt an input voltage change. Personel injury
or equipment damage may occur if done
incorrectly.
WARNING: The fuse should be replaced or the
voltage should be reset only when the power
cord has been disconnected from its power
source.
[2] 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.
[3] 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
Recordin/PA output [9] for recording or other
purposes.
WARNING: Never play the CLASSIC-SE without a
speaker connected if the Speaker On/Off switch
[3] is in the “On” position. This may cause
serious damage to either the power tube 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 TUBE,
REMOVE THE SAFETY GRILL FIRST.

AFTER REPLACING THE POWER TUBE, PUT
THE SAFETY GRILL BACK IN PLACE.
NOTE: The CLASSIC-SE has an auto-bias circuit so
it does not have to be rebiased after replacing the
power tube.
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 TUBE (ECC83, 12AX7, 7025):
- Microphonic whistling or squealing.
- No or low amp volume.
- Excessive noise.
POWER TUBE (EL84, 6V6, 5881, EL34, 6L6):
- 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, the POWER TUBE can be
replaced without rebiasing.
Again, if you have any doubts, please take no
risks and consult your dealer and/or a qualified
technician.