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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.
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; High voltages are present inside the
amplifier and on exposed valve sockets when valves
are removed, so take suitable care. It is not
necessary to remove the bottom cover. Beware
valves get hot in operation!
How do I know when to replace valves?
Generally speaking valve failure may be one of these:
1, The valve continues to work but the emission gets
low. In the case of output valves this will result in not
being able to set the bias.
2, The valve gets noisy/microphonic. Usually happens
to the small valves, and can be confirmed by tapping
with a pencil.
3, Heater fails. No glow in centre of valve. Valve is cold.
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 at all.
4, Dramatic Failure. Occasionally the demise of a
power valve may be obvious with internal sparks and
noise through the speakers. In that case, switch off and
do not use until a replacement is available. Before use
see chapter 6 "Bias Adjustment". If there was any
associated burning smell etc, we would recommend a
qualified person examines the inside of the amplifier first.
If the amplifier sounds OK the valves are probably fine. If
the emission drops you will have difficulty setting the
bias for the output valves.
Valve life will depend upon such things as hours of use
and number of on/off cycles. It is not good practice to
remove the valves unnecessarily as this can strain the
pins and cause tiny air leaks. If the amplifier has had
regular use of 4 years of more the amplifier will probably
benefit from a valve change.
5, Changing valves:
Before changing the 845i valves ensure that it safe to do
so by switching off and removing the mains plug at least
20 minutes before hand. This will enable dangerous
voltages to dissipate, and the valves to cool down.
If possible check the bias setting before you attempt to
change the valve(s), in order to familiarise yourself with
the procedure.
If changing 845 valves you will need to check and if
necessary adjust the bias as the new valves will
probably be a different bias. Most people find it easier to
do a course adjustment (within 10% of 180mv), and then
do a final adjustment when the amplifier is fully warmed
up.
If all is well there should be no more than a barely
detectable hum from the speakers, and the amplifier
should sound OK when tested. You may need to adjust
the "Hum Adj" screw, see section 6.
6, If you cannot set up 180mv, then the valve is
probably faulty or is unsuitable. (if the reading is zero
the individual fuse may be blown).
If the valves are brand new, you will need to check
again after approximately 10 & 100 hours, after that
only occasionally or if you suspect a problem.
7, To avoid damage to the amplifier and electric
shock hazard you must use only valves marked
845, 6SL7, 6SN7 or equivalent. Use only valves
which you know to be new or good condition and test
the amplifier thoroughly before resuming normal use.
8, Replacing the small valves:
6SL7 (6188) and 6SN7 (CV181). Neither of these
requires any set up procedure. It's just 'plug and play'
although care should be taken when removing and
inserting not to bend the pins. If this happens gently
bend the pins back into shape. (These valves are
similar with the same pin connection; accidentally
interchanging these two valves would not cause
damage, buy will reduce the amplifier performance).
Icon Audio are happy to check the valves/amp or re-
bias your amp free of charge.
(For Engineers with technical knowledge, the correct
bias setting is 42ma through the 4.3 Ohm tertiary
winding of the transformer, which will give 180mv
DC).
8 Specification & Features
(Typical conditions @ 235v 50Hz)
845 output valves (only)
6SL7 double triodes for first stage (6188 eqv)
6SN7 double triodes for 2
Hand wired point to point components
No printed circuit board
Ceramic valve bases for low noise/leakage
80w RMS at clipping
Signal to noise level -105dB
Freq response 20Hz-20kHz ±1db
Power bandwidth -3db=10Hz-40kHz
0.3% THD typical 8w (0.1% 1w) 1khz
Custom hand wound transformers using
Japanese long grain steel
Supplied with attractive safety guard
Minimal feedback used
High quality oversized metal film resistors
Audiophile High quality polypropylene or Jensen
audio capacitors (optional upgrade)
Internal wiring using silver PTFE audio cable
Valves carefully matched for best performance
Gold plated Input & speaker terminals
400 mv sensitivity for full output (High)
900 mv sensitivity for full output (Low)
230/240volts, 180watts (zero signal)
3 amp T mains rear fuse (with spare)
500 ma T 845 anode fuses (with spares)
W:22cm. D:52cm. H:29cm. Weight:23kg
IEC mains lead, (5amp fused)
CE certified. ROHS & WEEE compliant
Specification subject to change without notice.
nd
stage (CV181 eqv)
Page 8
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