icon Audio MB 845, Instruction Manual

Page: 8 / 9

Page 8
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, can be confirmed by tapping with a
pen.
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 chapt
er 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, 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.
5, Changing valves:
Before changing the 845 valves ensure that it safe to do
so by switching off and removing the mains plug at least
30 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 all the 845s be ready to adjust the bias in
order not to overload the power supply.
Don’t worry how
low the reading goes this will not cause damage. Do 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.
6, If you cannot set up 400mv, 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 and 6SN7.
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 may
reduce the amplifier performance).
Icon Audio are happy to check the valves/amp or re-
bias your amp free of charge.
8 Specification & Features
(Typical conditions @ 240v 50Hz)
•
845 output valves
•
6SL7 (6N8) double triodes for 1st stage
•
6SN7/CV181 (6N7) double triodes for 2
nd
stage
•
Hand wired point to point components
•
No printed circuit board
•
Ceramic valve bases for low noise/leakage
•
90w RMS at clipping
•
Signal to noise level -95db
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•
Freq response 20Hz-20kHz +or- 0.1db
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•
Power bandwidth -3db=10Hz-30kHz
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•
0.1% THD typical 8w (0.015% 1w) 1khz
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•
Icon Audio custom hand wound transformers
•
Supplied with attractive safety guard
•
Minimal feedback high ?? Low ??
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•
High quality oversized metal film resistors
•
High quality polypropylene or Jensen audio
capacitors (optional upgrade)
•
Internal wiring silver plated PTFE audio cable
•
Valves carefully matched for best performance
•
Gold plated Input & speaker terminals
•
400 mv sensitivity for full output (High)
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•
1.4 v sensitivity for full output (Low)
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•
230/240volts, 200watts (zero signal)
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•
1x 3 amp T mains rear fuse (with spare)
•
2x 250 ma F 845 anode fuses (with spares)
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•
W:20cm. D:50cm. H:22cm. Weight:22kg
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•
IEC mains lead
•
CE certified. ROHS & WEEE compliant
Specification subject to change without notice.