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10. TROUBLESHOOTING
Hum and crackling
Hum in an audio system is often caused by several system components being earthed individu-
ally. It is particularly common with tuners, VCRs or satellite receivers where the earthed aerial
cables can cause a hum loop via the aerial input.
Tube power amplifiers are normally earthed, and the V 70 is no exception. However, removing
the earth wire on your mains plugs is not a solution, You can isolate the aerial earth connection
with a special signal isolator. This device has no adverse affect on the sound or picture quality
of tuners or TVs.
Check also that the phono plugs are a tight fit. Bend the outer earth contact inwards slightly if
necessary. Sometimes the internal pin in a phono plug may not be a tight enough fit, in which
case you should change either the interconnect cable or the socket.
Switching interference
Older fridges and 12 V halogen lamps can cause cracking through the loudspeakers when they
switch on and off.
Solution: The only solution is to use a single power socket board for your entire system and to
use a different power outlet in your listening room. However, it is not always possible
to eliminate the problem entirely.
Channels are not balanced
1. Damaged cables and poorly fitting phono plugs can create resistance in the signal path
enough to reduce the output level of one channel.
Solution: Try new cables or clean the plugs and sockets with isopropyl alcohol.
2. A tape or DAT machine connected to the REC Out may have a faulty Record input (or
faulty interconnect cable) causing the signal to overload. This can result in an imbalance
between the left and right channels.
Solution: Disconnect the tape/DAT machine
3. A faulty output tube can cause a drop in output in one channel and generate distortion at
higher output levels.
Solution: Locate the defective tube using the bias adjustment facility. Replace the
tube.
Increased hiss on one channel
An irregular hissing sound is a sign of a worn driver tube.
Solution: Replace the worn tube.
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