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7. Service: Should you suspect a problem, you could
return the unit to your dealer or Icon Audio for a periodic
service or return the valves for testing free of charge.
You should carefully remove the valves (the 845s 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 normally hard wired to work on 230/240v
ac (115-120v ac USA). The transformer may be re-
configured for 110/120v ac by a qualified engineer. See
engineers notes or contact Icon Audio for more
information.
This manual is provided for guidance only, and is not
intended as a comprehensive service manual. In case of
problems you should refer to your dealer or directly to
Icon Audio.
6 Bias Adjustment 845s
In most cases a quick check of the bias of each 845
is all that is necessary. Only occasionally will any
adjustment be necessary.
Please 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.
When checking the bias ensure that any "Active"
pre-amp or source is "off" with zero volume to
prevent false readings. Passive pre-amps should
have "zero" volume. On a test bench "short circuit"
the input.
The ST 845s use the "fixed bias' mode of valve
operation. This has the advantage of higher power, and
cooler running. However regular checking (say once a
month), is advisable to check the bias reading using the
built in meter to ensure best performance from the
amplifier.
It is recommended that the bias is checked regularly. But
even if the reading is slightly over or under no action
may be necessary if all readings are the same, as this
may be your local 230/115v power variations. If you find
variations at different times of the day it is better to play
safe and be "under" rather than "over". The performance
of the amplifier will be unaffected. Ideally they should
read the same.
1, Tools you will need:
For checking none. For adjusting a small flat blade
screwdriver. (preferably a long one).
BEWARE The 845 valves get very hot!
2, Adjustment Method This is done at zero volume with
speakers connected. If possible first run the amplifier for
about 5 mins.
First select V1 with the "Bias" selector, the pointer should
be in or close to the black section. If not adjust until it is
correct.
The adjustment is very sensitive so adjust very
carefully.
Then select V2, and adjust if necessary.
Do the same for V3 and V4.
Check V1,V2,V3,V4 again and make small adjustments
if necessary.
*See engineers notes at rear
Check regularly at switch on. Regular adjustment
should not be necessary.
3, Notes on Bias adjustment:
If the reading appears a little unstable this is normally
due to mains fluctuations. Make sure you have the
BIAS switch set to the correct 845 valve.
4, Bias cannot be set (but the valve is lit):
No reading: May be a blown internal fuse or faulty
845.
Reading too low: Valve may be worn out.
Reading too high: Valve may have developed a
fault.
It is often possible to prove if the problem is a valve
or the amplifier by swapping around valves by a
process of elimination.
5. Valve Testing:
If you suspect any of the valves are not working
correctly Icon Audio will test the valves at no charge.
Return them to us well packed in a rigid box with a
note detailing the problem, which valves you suspect
and your contact details. We will then contact you
with the test results.
Possible valve faults
Not all valve faults are visible but 845s and driver
valves should not be used if:
1. The "silver" getter material has turned white
or is disappearing, normally due to an air leak.
1. The valve rattles excessively (a slight rattle is
normal).
2. Cracks in the glass.
3. The base has become loose.
4. Any valve pins are damaged or loose.
5. Heaters not lighting up (this is harder to see
with the 6SL7/6SN7). If one valve stays
"cold" the heater has probably failed.
NO BIAS ADJUSTMENT NEEDED FOR THE
SMALL VALVES. 6SL7, 6SN7/CV181, GZ34/5AR4
NOTE!
If there is no reading at all the internal fuse individual
to each 845 should be checked by a qualified
engineer. Spares should be attached to the inside of
the bottom plate.
After significant bias adjustment or valve change the
hum adjustment MAY be necessary if you notice
increased background hum. See section 5.4.
7 Valve Replacement
Important!
Do not attempt to change the 845
output valves without reading these notes.
Failure to do so could be both dangerous to you
and damaging to the amplifier. Keep these notes
handy.
6SN7/6SL7 Take care that you orient the valve
correctly before inserting. Line up the centre
"Spigot" first. They are easy to break, do not
bend excessively to the side.
Health & safety; DANGER High voltages are
present inside the amplifier and on exposed valve
sockets when valves are removed. You must
remove the power cable from the rear before
making any changes. It is not necessary to
remove the bottom cover. Beware valves get hot
in operation!
Page 7
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