Page 7
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: You should if possible check the
bias setting before you attempt to change the valve(s), in
order to familiarise your self with the procedure.
The safe way to change especially if they are a different
type is to change and re-bias one pair at a time.
Remove the first pair of old valves and fit the
replacement pair. Switch on and measure and adjust the
bias.
Do not allow the reading to go above 95
. Don’t worry
how low the reading goes this will not cause damage.
Continue in the same way and fit all four valves. 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 the bias then the valve is probably
faulty or is unsuitable.
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.
NOTE: If you are changing to a different type of
valve, be ready to change the bias quickly, as the
setting from say KT88 to EL34 may be quite large.
Use the “standby” switch to cut power to the valve.
7, To avoid damage to the amplifier and electric
shock hazard you must use only valves marked
KT88/EL34 (or 6550, 6CA7, KT66, KT77, 6L6, 5881),
6SL7/6N9C/6188, 6SN7/6N8/CV181 Or that you know
to be direct equivalents.
Use only valves which you
know to be new or good condition and test the amplifier
thoroughly before resuming normal use. The new high
power KT120/KT150 are not recommended as they will
exceed the maximum heater power and power
transformer burn-out may result.
8, Replacing the small valves:
6SL7 (centre) and 6SN7 valves.
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 break the centre spigot. (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.
9, GZ34/5AR4 Rectifier.
Generally these last about the
same audio valves, they generally get weaker after
several years so we recommend replacement when
replacing output valves otherwise the amplifiers
performance and power may be reduced. Replacements
may be obtained from Icon Audio. The 274B is not
strong enough for the ST40, arcing and premature failure
is likely.
Explanation:
*
RMS watts
Do not literally exist! But this figure is based upon the RMS
voltage output (V²/R).
*Push Pull
is a very elegant way of virtually cancelling out non linear
distortion, noise and hum. Whilst dramatically increasing the power and
damping factor. In Class AB about 1/4 of the output is pure class A. Unlike
transistor designs there is NO crossover distortion before the amplifier
reaches full output.
*Ultralinear
(or Distributed Load). This is a true “win-win” output stage
design. Having virtually the all the characteristics and low distortion of pure
Triode valves, whilst keeping 90% of the power of pure Pentodes types. But
still inferior to pure triode.
*
The Leak Stereo 20
(& 50/60) series used a single ECC83 triode first
stage coupled to an ECC83 double triode “long tailed pair” phase splitter.
Originally developed by A D
Blumlein in the 1930’s. This design was also
widely used by GEC, Mullard, Sugden etc. However the “TL+” series used
an EF86 Pentode, now widely regarded as having an inferior sound).
*Power output
level will vary from 25 watts (6L6) up to 45 watts (KT88)
depending upon the output valve type.
7 Specification & Features
(Typical conditions @ 230v 50Hz)
•
KT88/EL34 output valves or eqv (6550)
•
6SL7/6H9C double triodes for first stage
•
6SN7 double triodes phase-splitter
•
GZ34/5AR4 full wave rectifier
•
Low or medium feedback used (L and H)
•
Icon designed and manufactured Tertiary wound
output transformers
•
Hand wired point to point components
•
No printed circuit board
•
Ceramic valve bases for low noise/leakage
•
40w RMS per channel Ultralinear
•
20w RMS per channel Triode mode
•
Signal to noise level -90db
•
Freq response 20-20kHz +0-.5db 28w UL
•
Freq response 15-25kHz +0-1db 28w UL
•
0.15% THD at 8 watts
•
Channel balance typically less than 0.2dB
•
4 and 8 ohms output taps
•
Choke regulated power supply
•
Supplied with attractive valve cover
•
Audiophile quality metal film resistors
•
Audiophile quality polypropylene audio caps
•
Japanese ALPS volume pot.
•
Rubicon/Nichichron power caps.
•
Internal wiring using PTFE silver plated cable
•
Valves carefully matched for best performance
•
Gold plated Input & speaker terminals
•
Inputs for CD, Tape, Tuner, Aux
•
Record loop with monitor switch
•
250mv sensitivity for full output
“H”
•
800mv sensitivity for full output “L”
•
220-240volts, 76w SB, 140w Min, 240watts max
•
1.6 amp (3amp USA) AS rear fuse (with spare)
•
390W, 210H, 410D Amp overall 25kg
•
Carton= 34x51x49cm 28kg packed
•
IEC mains lead, (5amp fused)
•
Conforms to CE ROHS and WEEE where applicable
Specification subject to change without notice.
