Page 7
7 Valve Replacement
Important!
Do not attempt to change the KT120
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.
The KT120 version of this amplifier can only be used
with KT88s if the power supply is de-rated
(engineers job ask us for info). Although KT120s
may be used in the KT88 version, the full power and
quality will not be realised unless the power supply
is up-rated
7
(by an engineer).
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 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, 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:
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 KT120s 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 300mv, 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
KT120, KT90, KT88 (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 and 6SN7.
Neither of these requires any set up
procedure. Care should be taken when removing and
inserting not to break the locating spigot and keyway.
(Accidental swapping of these two valves will not
cause damage).
Icon Audio are happy to check the valves/amp or re-
bias your amp free of charge.
8 Specification & Features
(Typical conditions @ 240v 50Hz)
KT120/88 output valves or eqv (6550)
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)
115w RMS (KT120) Ultralinear
60w RMS (KT120) Triode mode
Signal to noise level -95db
Freq response 20Hz-20kHz +or- 0.1db
Power bandwidth -3db=10Hz-30kHz
0.1% THD typical 8w (0.015% 1w) 1khz
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
Internal wiring using silver gilt cable
Valves carefully matched for best performance
Gold plated Input & speaker terminals
450 mv sensitivity for full output (High)
900 mv sensitivity for full output (Low)
230/240volts, 150watts (zero signal)
Standby switch function
3 amp T mains rear fuse (with spare)
500ma AS HT fuses (with spares)
W:20cm. D:50cm. H:22cm. Weight:22kg
IEC mains lead, (5amp fused)
CE certified. ROHS & WEEE compliant
Specification subject to change without notice.
