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Distorted sound.
Try another source; if sound improves then it's probably
something wrong with the first source. If no improvement
try different speakers, if no improvement it is likely to be
an amplifier problem.
Distorted sound at higher volumes may be because one
of the output KT88 valves is not working. This could be
due a faulty KT88 or one of the KT88 internal fuses
blowing. A symptom of this would be no 9v bias voltage
at the test point. Refer to an engineer or Icon.
Hum Problems
If you experience hum, try disconnecting all inputs, if
hum persists this is probably an amplifier fault.
If not, identify which input is causing hum. Connect one
input at a time. A common cause is a 'hum loop' caused
by having to many earths, and may be identified by
unplugging each input source from the mains. One
remedy for this is to use an interconnect which only has
the screen connected at one end. Other causes of low-
level hum can be from adjacent equipment, so
experiment with moving equipment around to see if this
makes the hum better or worse.
One channel missing.
Usually 'bad' connection on either the input or the
speakers. Try swapping the connection over to establish
if the cause is:
(a) Input to the amp.
channel.
(b) Amplifier or speakers.
If you have connected both a known good input and a
known good speaker to a particular channel without
success the fault is probably within the amplifier.
Strange noises coming from speakers
Turn volume to minimum on unused input, if the noise
disappears, the fault is with the source or the connection.
If noise persists, the problem is with amplifier.
If a whole output valve glows red (other than the heater),
often accompanied by a hum through the speakers,
switch off immediately, and refer to Icon Audio or a
service engineer, as this could be valve failure.
A valve that is lit up is not a guarantee that it is working
properly; conversely a valve that is not lit up will not be
working.
Valve Replacement (see also section 7)
Valve life will depend upon such things as hours of use
and number of on/off cycles, the Standby/HT Delay
Circuit if fitted will extend the life of the valve by not
stressing the cathode when it is cold. It is not good
practice to remove the valves unnecessarily as this can
strain the pins and cause tiny air leaks.
Service: Should you suspect a problem, you could
return the unit to Icon Audio for a periodic service or
return the valves for testing free of charge. You should
carefully remove the valves (the KT88s should be held
by the base when removing, to prevent damage)
numbering them with a marker from left to right as you
do so in order that that may be replaced in the same
position. They should be well packed in cardboard &
foam or similar, and returned to Icon Audio for testing.
(Valves are very rugged if packed properly).
Mains Supply
This amplifier is hard wired to work on 230/240v ac. The
transformer may be re-configured for 110/120v ac by a
qualified engineer. Contact for more information.
Sound will move to the other
Sound will not move.
6 Bias Adjustment
Read these notes all the way through first.
If you are unsure about any aspect contact your
retailer, Icon Audio or a competent service
engineer.
The Stereo 50i Classic uses the Icon "semi fixed
bias' mode of valve operation. This will only rarely
need adjusting if at all as the amplifier can
compensate for some valve deterioration. There is
only one adjustment. This has the advantage of
higher
power,
and
occasionally (once a year) it is advisable to check the
bias reading using the supplied meter to ensure best
performance from the amplifier. This is a safe
procedure which involves measuring 9v DC in the
four sockets next to each KT88 and adjusting if
necessary.
1, Tools you will need: The supplied meter or one set
to measure approx approx 20v (DC), and a small flat
blade screwdriver. Adjustment is done at zero
volume with speakers connected. Run the amplifier
for about 10 mins (if possible) first.
2, Connect: the black probe to the chassis 'earth' by
unscrewing the '0' speaker terminal and tightening
the probe in the exposed hole. And the other in the
test socket adjacent to the valve on test. Set the
'Icon' meter to 20v or the 'black mark'. See pics.
Making the 'earth' connection.
3, Checking Bias: You should get a reading of ideally
9v if each valve is conducting correctly. But this will
vary from about 7v to 10v. Bear in mind that your
mains voltage fluctuations can affect your readings
up to about 10%.
Showing a probe reading 1
cooler
running.
However
st
output valve
Page 6
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