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Interference Problems
The amplifier design incorporates features and devices
which make it resistant to mains-born interference. But
some CH boilers/fridges/cookers etc can generate RF
(radio frequency) interference which travels through the
air (and walls). Although rare this can be very irritating.
Usually a simple cure by fitting a capacitor to the
offending unit will effect a cure (ask us).
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.
Also see internal fuses above
Strange noises coming from speakers:
Turn volume to minimum on unused input, if problem
corrected either fault with source unit or with connection.
If noise persists, problem 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 (usually cold to the touch).
Valve Replacement (see also section 7)
Valve life will depend upon such things as hours of use
and number of on/off cycles, Do not switch on and off
unnecessarily (see Standby). Also 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 (hold the base when
removing, to prevent detaching the glass) 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 easily be re-configured for 110/120v ac.
Contact us for more information.
6. Bias Checking & Adjustment
The bias voltage for this amplifier is 330mv DC
The Stereo 40 6AS7 uses the 'Split Bias' method of
valve operation. This has the advantage of higher
power, lower feedback and cooler running. However
it is important that the bias is checked at least twice
a year using the supplied meter to ensure best
performance from the amplifier.
This is a safe procedure which involves measuring
0.33v/330mv in each of the four sockets next to each
6AS7 and adjusting if necessary. This need not be 100%
accuracy and minus 10% i.e. 300mv to 350mv will have
virtually no effect.
Sound will move to the other
Sound will not move.
1, Tools you will need: The supplied meter or one set
to measure approx 2 or 3 volts DC, and a small flat
blade screwdriver. Adjustments are done at zero
volume with speakers connected. Run the amp for at
least 20 mins (if it is working correctly). Otherwise do
a rough adjustment and check later when the ST40 is
hot.
The Icon meter reads in mv (millivolt=1v/1000). So
0.33v will read "330mv".
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. See pics..
Set the 'Icon' meter to 2000mv (2v) or the 'black
mark'.
Making the 'earth' connection.
3, Checking: You should get a reading of 330mv if
the valve is working correctly. But bear in mind that
your mains voltage fluctuations can affect your
readings up to 10%. Check all valves, they should be
within about 10% of the ideal voltage.
4, Adjusting: If the reading is incorrect, set this by
using the bias adjuster in the centre. They are very
sensitive so adjust very carefully; use tiny turns of the
screw. If the reading appears a little unstable this is
normally due to mains fluctuations.
5, If one or more valves are showing erratic readings
or you cannot set the correct voltage, then that valve
is probably faulty or out of specification. If you are
unable to set the reading high enough this means the
emission of the valve is low.
Showing a probe reading 1
If you are unsure about any aspect of bias contact
your retailer, Icon Audio or a competent service
engineer. Icon Audio provides a free bias check and
"health check" for your amplifier and valves.
st
output valve
Page 7
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