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4 Getting the best performance from your amplifier
•
Do not leave the amplifier switched on all the time. This is not necessary
•
Do not switch off and on without a short rest of 60 seconds
(to reset the ‘soft start’)
•
Do not adjust the output valve grid bias without reading the manual
•
Do not switch from Ultralinear to Triode without first switching
to “Standby”
•
Do not operate the amplifier without loudspeakers connected
•
Do not use valves other than listed as there could be danger of shock or damage
•
Make sure the speakers are in phase.
•
Use the best possible source material.
•
Use efficient, well-designed speakers.
What is safe maximum volume?
The MB 90 will run happily all day long at
maximum power; the valves are not stressed any
more at full power than at zero volume. Running
into gross distortion will however stress the whole
amplifier. Generally speaking if the sound is not
distorted then the amplifier is not stressed.
Triode Switch.
This switch causes the KT90s to
operate as Triode valves.
As switching can
stress the output transformers switching
should only be done when the amplifier is in
the “standby” mode or switched off.
You may
notice that there is a slight reduction in volume in
Triode mode; this is due to the lower gain that
output valves have in this mode, advance volume
to compensate.
Leaving the amp switched on
We have been asked if the amp 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. Use the
Standby switch when not continuously in use, to
avoid switching on and off unnecessarily.
Standby switch
This switch leaves the valves heated but without
power. This preve
nts “Cathode stripping” at switch
on, allows the cathode chemistry to re-form,
minimises energy usage, and makes the amplifier
available for instant use. However as a general
guide it is not recommended that this mode
should be continuously used for more than 24hrs.
We would always advise that any item of home
electronics is switched off when unattended.
‘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, have a better
service life and maintain their performance longer.
The upgrade valves supplied with selected
models 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.
Cabinet Care
To remove dust we suggest gentle brushing of the
polished stainless steel cabinet with a 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, and always clean with the power
disconnected.
5 Trouble Shooting
Amplifier Dead
Check the 3 amp mains fuse 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 is a fault you should disconnect
from the mains and seek qualified help or Icon Audio.
Replacements should be 3
Amp ‘anti-surge’.
The fuse in the wall plug should be a 3 or 5 amp fuse,
although unlikely to fail, this should be checked if the
amplifier fuse is OK.
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?
Distorted sound.
Try another source; if sound improves then it’s
probably something wrong with the first source. If no
improvement
try
different
speakers,
if
no
improvement there may be an amplifier problem.
Distorted sound at higher volumes may be because
one of the output KT90 valves is not working. This
could be due a faulty KT90 or one of the KT90
internal fuses blowing. A symptom of this would be
no 0.5V bias voltage at the test point. Refer to an
engineer or to Icon Audio.