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4, Adjusting: If all the valves are high or low, set the 9v
by using the single adjusting screw. If one valve is
significantly higher or lower, then it may be faulty or life
expired. The adjustment is very sensitive so adjust very
carefully. If the reading appears a little unstable this is
normally due to mains fluctuations. The Stereo 50 uses
semi-fixed bias, where the KT88 is allowed to find its
own individual fine bias level. Only occasional checking
should be necessary. Bear in mind that valves with an
output of up to 25% below the others are unlikely to have
much of an audible effect of the sound at normal
listening levels.
8 Valve Replacement
Important!
Do not attempt to change the KT88
output valves without reading these notes. Failure to
do so could be both dangerous 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.
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!
5, Changing valves: If possible check the bias setting
before you attempt to change the valve(s), in order to
familiarise yourself with the procedure.
Use a good quality KT88 matched set. This will stop
wide variations in bias voltage. Matched sets and odd
valves may be obtained from Icon Audio.
If changing all the KT88s be ready to adjust the bias in
order not to overload the power supply. Do not allow the
reading to go above 12v temporarily whilst you are
adjusting. 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 7v, then the valve is probably
faulty or is unsuitable. (if the reading is zero the
individual fuse may be blown, spares inside).
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
KT88 (or 6550), 6SL7, 6SN7. 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 (middle) and 6SN7 (outer pair). 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; accidental wrong insertion would not
cause damage).
Icon Audio are happy to check the valves/amp or
your re-bias your amp free of charge.
6 Specification & Features
(Typical conditions @ 240v 50Hz)
KT88/6550 output valves
6SL7 double triodes for first stage
6SN7 double triodes phase-splitter
Hand wired point to point components
No printed circuit board
No tag board
Ceramic valve bases for low noise/leakage
HT delay circuit to protect cathodes (optional)
55w RMS per channel Ultralinear
27w RMS per channel Triode mode
Signal to noise level -90db
Freq response 20-20khz +or- 0.1db
Power bandwidth 10hz-30khz
0.1% THD
Custom hand wound transformers using
Japanese long grain steel
Choke regulated power supply inc output
Supplied with attractive safety guard
Minimal feedback used
High quality oversized metal film & wire wound
resistors
Audiophile High quality polypropylene audio caps
Japanese 'Blue' ALPS volume pot.
Internal wiring using silver gilt cable
Valves carefully matched for best performance
Gold plated Input & speaker terminals
Inputs for CD, Tape, Tuner, Aux
Tape monitor loop
300 mv sensitivity for full output (integrated)
1000mv sensitivity for full output (power-amp)
230/240volts, 150watts (zero signal)
Standby consumption
3.15 amp rear fuse (with spare)
400W, 380D, 220H, 23kg
IEC mains lead, (5amp fused)
CE certified. ROHS & WEEE compliant
Specification subject to change without notice.
Page 7
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