Koch TWINTONE III - Handbuch (Seite 5)

This fuse also must be replaced with the same type and value
in order to avoid damage to the amp and to prevent voiding the
warranty.
[4] FS-4 FOOTSWITCH CONNECTOR: Provides an input for the
FS-4 footswitch and disconnects the CHANNELS [5] and the GAIN
BOOST [FP 4] switch, when the footswitch is plugged in.
FS-4 FOOTSWITCH
The included FS-4 Footswitch is equipped with four switches:
- CHANNELS switch for selecting channels [Overdrive channel = red
LED ON].
- BOOST switch for activating the Gain Boost in the Overdrive
channel (red LED).
- REVERB/FX switch for activating the reverb or the parallel effects
loop (yellow LED).
- RHYTHM/SOLO switch for selecting Rhythm volume [9] or Solo
volume [10] (Solo = green LED ON).
[5] CHANNELS SWITCH: Selects the Clean or the Overdrive
channel if the FS-4 Footswitch is not connected.
[6] REVERB/FX MIX VOLUME: Controls the amount of the Spring
Reverb or Effects signal mixed with the original dry signal (see [8]).
NOTE: If the FS-4 Footswitch is not connected, the Reverb is
activated.
[7] SERIAL/PARALLEL - TO FX-IN (=SEND): This jack provides a
buffered mono output from the preamp of the TWINTONE-III and can
be used to connect an external effects unit. This jack must be
connected with the input of the effects unit (see also CONNECTION
DIAGRAM).
[8] SERIAL - FROM FX-OUT (=RETURN): This jack provides an
input for an external effects unit and must be connected to the output
of the unit. When used, it disconnects the preamp of the
TWINTONE-III from the power amp.
[9] PARALLEL - FROM FX-OUT (=RETURN): This jack provides an
input for an external effects unit and must be connected to the output
of the unit. When used, it disconnects the internal spring reverb of
the TWINTONE-III and allows the REVERB/FX MIX control [6] to
adjust the volume of the external effects signal.
If this loop is used, direct signal must be taken off the effects
unit's signal. For example by turning the effects unit's ‘dry/wet’
control to ‘wet’.
NOTE: This effects loop operates on a -10dBV signal level which
guarantees compatibility with both instrument-level effects like floor-
pedals and guitar-processors, as well as line-level effects like
professional 19 inch rack mount devices.
If connecting an effects unit to the TWINTONE-III causes hum, a
ground-loop may be the cause of it.
[10] SPEAKER OUTPUT JACKS: Provided for connection of
speaker(s) or speaker cabinet(s) with an impedance of 1x4/2x8
ohms, OR 1x8/2x16 ohms, OR 1x16 ohms. (see also CONNECTION
DIAGRAM page)
WARNING: Never play the TWINTONE-III without a speaker
connected. This may cause serious damage to either the power
tubes and/or the output transformer.
ALWAYS USE SPEAKER CABLE.
[11] REC/PA OUTPUT: ThIs jack provides a mono output from the
power amp and includes Reverb and External Effects signals. The
signal is derived from the speaker output and filtered by a special
Filter which simulates the sound coming from the speaker, so it can
be fed directly into a recording or sound reinforcement mixer.
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 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.
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 TWINTONE-III’s 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 (EL34):
- 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 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