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Leaving the amp switched on
We are often asked if the amplifier should be left
running 24/7 without switching off. Whilst the
amplifier will sound at its best when it is properly
warmed up, there is no advantage leaving it switched
on when it is not in use. It is using electricity and as
valves have a finite life, their life could be used up in
as little as 6 to 9 months.
'Burning in'
Although the amplifier should sound good within
about 10 mins it can take up to an hour to sound at
its best and will take several months of regular use
before it is fully 'run in'.
Upgrading Valves!
Quality valves should sound better and have a better
service life. The valves supplied with selected models
1. Amplifier Dead (nothing working)?
Check the 5 (or 10amp for 115 V) amp mains fuse in the
IEC socket at the back of the amplifier. To gain access,
remove the mains lead. The fuse is in a small plastic
drawer, which forms part of the socket assembly. To
open insert a flat blade screwdriver or similar and prise
open. The fuse in use is the innermost the outer is a
spare. Should the replacement fuse also blow there
obviously a fault. You should disconnect from the mains
and seek qualified help or contact Icon Audio.
Replacements should be 5 (or 10 amp) Amp 'anti-surge'
type. Available FREE from Icon Audio on Request.
(UK only) The fuse in the wall plug should be a 5 amp
fuse, although unlikely to fail, this should be checked if
the amplifier fuse is OK.
2. Lights up but one or both channels not working
Check for no bias voltage for one channel according to
the built in meter. 845s that are lit but without their HT
high voltage will not get very hot compared to normal.
There are also two HT fuse's inside the amplifier. One
for each channel. This would not normally blow unless
there is a valve fault or an overload condition. These
carry a potentially lethal very high voltage which takes
time to discharge after power off. This should be
checked by your dealer, or only if you are a competent
engineer. Disconnect amplifier from the mains power
and wait 20 minutes before removing bottom plate. If the
HT fuse has blown, there are replacements inside.
Replace bottom cover afterwards and check bias
immediately after switching on. If the replacement fuse
blows there is a fault. Seek qualified help.
It is unlikely that both channel fuses would blow unless
the output has been overloaded.
2a. No sound
Have you selected the right input? Is the "Tape Monitor"
switch up? Are all the connections OK? Is everything
switched on? Are the speakers connected?
Is the bias voltage present on all 845s? A working
amplifier should have a very low hum in both speakers.
Distorted sound.
Could be your source, the speakers or the amplifier,
check all wiring, and try swapping things around to
eliminate or prove which component is the problem.
Both channels or just left or right? If both could be your
source unit. Try another source. If one channel is
distorted check the bias. No bias reading means either a
fuse blown or a faulty valve. Distorted sound at higher
*See engineers notes at rear
are the result of careful comparison with other
makes. But beware of paying a premium for "New
Old Stock" valves where you may be paying for rarity
value and not performance. Icon Audio normally keep
a range of upgrade valves in stock. Ideally valves
should be tested an ST845 before purchase. Note
that premium valves may not last any longer and are
not necessarily any more reliable.
Cabinet Care
To remove dust we suggest gentle brushing of the
chassis with soft paintbrush. Other marks can usually
be removed with a damp cloth. The Perspex valve
cover may need a gentle wipe with soapy water and
drying with a duster. Never use anything wet on the
amplifier,
disconnected.
5 Trouble Shooting
volumes may be because one of the output 845
valves is not working. This could be due to a faulty
845.
3. Hum Problems
If you experience hum, try disconnecting the input, if
it clears it is external to the ST845 and further advice
should be sought from your dealer or see below. By
elimination find out which unit is causing this.
Interconnects should be well screened. Try another
interconnect.
If hum persists with no input this is probably the hum
adjustment.
4. How to adjust the "hum" adjustment:
Ideally use a AC millivolt meter connected to the
speaker terminals (together with loudspeaker) with a
shorted input, or no input connected. Adjust hum
adjustment for minimum hum (about 1mv or less AC).
OR Adjust by ear:
This is easier with one person listening another
adjusting, rotate adjustment backwards and forwards
for minimum hum (like tuning in a radio)
This will normally be necessary after changing 845
valves. Or after the amplifier has been in use for
some time. Check and adjust (if necessary) bias first.
5. External hum causes;
Identify which input is causing hum. Connect one
input at a time. A common cause is a 'hum loop'
caused by having too 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.
Never disconnect the mains earth. It is there for your
protection! (may not be used in some countries).
6. 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. This may blow the internal HT fuse.
and
always
clean
with
the
power
Page 6
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