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Replacing the 6AS7 Valves
Important: Do not attempt to change the 6AS7s
without reading these notes. Failure to do so could
be both dangerous and damaging to the amplifier.
When replacing valves, it is important that you use a
"matched quad" or two matched pairs if possible.
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 is to change and check one or two valves
at a time. Remove the first old valve and fit the
replacement. Switch on and measure bias, you should
be setting the reading for each valve to about 300mv
(0.3v), Do not allow the reading to go temporarily above
800mv. Don't worry how low the reading goes this will
not cause any problem. Continue in the same way and fit
all four valves. Do final adjustment when the amplifier is
fully warmed up.
TIP:
6AS7 valves can take a long time to stabilise, in which
case set to a lower level of say 250mv and increase by
small degrees until the 330mv is not exceeded when the
amp 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 300mv then the valve is
probably faulty, worn out or 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 brand of
valve, be ready to change the bias quickly, as the
difference in setting may be quite large.
7, VALVE TYPES: To avoid damage to the amplifier
and electric shock hazard you must use only output
valves marked 6AS7 (6080, Chinese 6N5, Russian
6H13), Driver valves marked 6SL7 (6N9/6H9/6188),
6SN7 (6N8/6H8/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.
DANGER!
THE ST40 6AS7 CAN ONLY USE THE 6AS7 VALVE.
(OR EQUIVALENT US 6080, Russian/China 6N5/6N13)
DO NOT USE ANY OTHER OUTPUT VALVE AS
DAMAGE WILL 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 re-
bias your amp free of charge.
9, 274B Rectifier. This should normally last
longer than the audio valves. Replacements may
be obtained from Icon Audio. Alternative valves
to use are GZ34, 5AR4, GU5.
*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.
7 Specification & Features
(Typical conditions @ 240v 50Hz)
•
6AS7 output valves
•
6SL7 double triodes for first stage
•
6SN7 double triodes phase-splitter
•
274B/GZ34/5AR4 full wave rectifier
•
No feedback used (integrated operation)
•
Icon hand wound transformers with Tertiary
winding. 5Ω cathode resistance
•
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)
•
22w RMS each channel @ clipping
•
Signal to noise level -90db
•
Freq response 20-20kHz ±1db
•
Power bandwidth 10hz-30khz
•
0.1% THD at 10 watts
•
4 and 8 ohms output taps
•
Choke regulated power supply
•
Supplied with attractive safety guard
•
Audiophile quality metal film resistors
•
Audiophile quality polypropylene audio caps
•
Japanese 'Blue' ALPS volume pot.
•
Rubicon/Nichichron power caps.
•
Internal wiring using PTFE silver cable
•
Valves carefully matched for best performance
•
Gold plated Input & speaker terminals
•
Inputs for CD, Tape, Tuner, Aux
•
Tape monitor
•
280mv sensitivity for full output (integrated)
•
680mv sensitivity for full output (power amp mode)
•
230/240volts, 76w SB, 185w Min, 260watts max
•
1.6 amp AS rear fuse (with spare)
•
Internal 2x 500ms AS (with spares)
•
390W, 210H, 410D Amp overall 23kg
•
Carton= 34x48x36cm 26kg packed
•
IEC mains lead, (5amp fused)
•
Conforms to CE ROHS and WEEE where applicable
Specification subject to change without notice.
Page 8
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