Koch ATR-4502 - Handbuch (Seite 5)

[2 & 3] SPEAKER OUTPUT JACKS: Provided for connection of (a) speaker cabinet(s) to
Channel A and/or Channel B in the STEREO or (SINGLE/DUAL) MONO mode, with a
minimum load of 4 ohms.
The output power of each channel changes with different loads as follows:
50 Watt: 1x 4 ohms or 2x 8 ohms speaker cabinet(s)
45 Watt: 1x 8 ohms or 2x 16 ohms speaker cabinet (s)
35 Watt: 1x 16 ohms speaker cabinet
[4] SPEAKER OUTPUT JACKS: Provided for connection of (a) speaker cabinet(s) in the
MONO (bridged) mode, with a minimum load of 8 ohms.
The output power changes with different loads as follows:
90 Watt: 1x 8 ohms or 2x 16 ohms speaker cabinet(s)
70 Watt: 1x 16 ohms speaker cabinet
DO NOT CONNECT A 4 OHMS OR TWO 8 OHMS SPEAKER CABINETS TO THIS
OUTPUT!
DO NOT USE GUITAR CABLE TO CONNECT THE SPEAKER CABINETS.
Use KOCH Dynacon SC608 speaker cable for the best results.
The ATR4502 can be used safely without a speaker connected.
Disconnecting the speaker(s) will NOT cause any damage to the amplifier.
[5] INPUT: Input for channel B.
[6] INPUT: Input for channel A in STEREO mode and for both channels in MONO mode.
[7 & 8] LEVEL: Switches for setting the signal level of channel A & B.
In the ‘down’ position the input level is 0dBV, which is well suited for mains operated
(studio) equipment.
In the ‘up’ position the input level is -10dBV, which is well suited for battery operated
equipment.
REPLACING TUBES
The ATR4502 has two 12AX7 tubes, one for each channel.
These tubes behave like strings, they lose highs, lows and dynamics and after a period of
time they have to be replaced to maintain the amps best performance. 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.
12AX7 tubes rarely fail. But if they are bad, these might be the symptoms:
- 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.
- Excessive hum on one or both channels.
Changing a tube can be a simple and quick fix for most problems in your amp.

SAFETY FIRST: DISCONNECT THE POWER CORD FROM ITS POWER SOURCE
AND LET HOT TUBES COOL.

REPLACE TUBES ONLY WITH ORIGINAL KOCH HIGH QUALITY TUBES. (IF
OTHER TUBES ARE USED THE WARRANTEE OBLIGATION EXPIRES)
If you have any doubts, please take no risks and let a qualified technician do the
job.