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4 How to get the best out of your amplifier
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Do not leave the amplifier switched on when not in use. Valve life will be reduced.
•
Do not switch off and on without a short rest of 60 se
conds (to reset the ‘soft start’).
•
Do not adjust the output valve grid bias unless you know how.
•
Do not switch from Ultralinear to Triode without switching to Standby to protect the transformer.
•
Do not operate the amplifier without loudspeakers connected.
•
Do not use valves other than listed as there could be danger of shock or damage.
•
Do check the bias regularly at least once a month for best performance.
•
Do make sure the speakers are in phase.
•
Do use the best possible source material.
•
Do use efficient, well-designed speakers.
What is safe maximum volume?
The Stereo 40 MK IV will run happily all day long
at a high volume; the valves are hardly stressed
any more than at zero volume. Running into
distortion will however stress the whole amplifier.
The maximum safe volume is just before distortion
occurs. However this will vary according to the
level and type of music played.
Triode Switch.
This switch causes the KT88s to
operate as Triode valves. Put the amplifier into
“Standby” first as switching without doing this
will stress the output transformers.
The
majority of listeners prefer the “triode” sound
believing it to be more pleasant to listen to, but the
power will drop to about 60% (30 watts). As the
gain in triode is nearly the same the volume will
be the same. But at higher volumes you may hear
some distortion as you are running out of power,
in which case switch to ULTRALINEAR. Maximum
continuous output reads 100% on the meter with
Triode being 75% on the meter. For best results
use “H” gain.
Headphone Use.
Higher impedance headphones
of 150-6
00Ω recommended. Plug in your
headphones to the socket on the front panel and
use the
“Headphone” switch to silence the
speakers.
If
for any reason the “0” speaker terminal is connected to
“ground” whilst in Headphone mode you may hear the
speakers working. In this case you must disconnect any device
which “grounds” the “0” speaker terminal.
Leaving the amplifier switched on
Do not leave the amplifier switched on 24/7. Your
valves will be worn out in approximately nine
months! 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. See (
Standby Switch). We would always
advise that any item of home electronics is
switched off when not in use
Standby Switch.
If the amplifier is not needed for
a few hours, it can be left in the “standby” state.
This enables the valves to be fully warmed and
ready to use the instant you put the standby
switch down. In the “standby” position the
amplifier is only using about 50% of normal
power. It also enables a healthy cloud of electrons
to build up around the hot cathode. Also it allows
the silver “getter” inside the valve to “mop up” any
gas that has built up inside and therefore keep the
vacuum “hard” for best performance. There is no
benefit to leaving the ST40 on standby
indefinitely. If not in use switch off!
‘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!
Good quality new valves sound better, have good
performance and reliability. The upgraded valves
supplied with selected models are the result of
careful comparison with other makes. But beware
of
paying excessive amounts for “New Old Stock”,
second hand valves. At this time we recommend
Genelex, E.H. Tung Sol, Shuguang, JJ, which we
are happy to test and supply.
Cabinet Care
To remove dust we suggest gentle brushing of the
cabinet paintwork with a soft paintbrush. Other
marks can usually be removed with a damp cloth.
On no account use anything wet on the amplifier,
and always clean with the power disconnected.
5 Trouble Shooting
1. Amplifier Dead
Check the 1.6 amp (3 amp USA) 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 bade 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. Replacements should be 1.6 (or 3
amp USA) a
mp ‘anti-surge’. Available from Icon
Audio free.
The fuse in the plug should be a 3 or 5 amp fuse,
although unlikely, this should be checked if the
amplifier fuse is OK.
2. No sound
ST40 lit up but no sound from either or one
channel. And t
he bias reading is “zero”. This could
be a HT fuse which are located inside the
amplifier.
Have you selected the right input? Are the
connections OK? Is everything switched on? Are
the speakers connected?
