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7 Valve Replacement
Important!
Do not attempt to change the 845
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.
6SN7/6SL7 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.
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?
Valve life will depend upon such things as hours of use
and number of on/off cycles. It is not good practice to
remove the valves unnecessarily as this can strain the
pins and cause tiny air leaks.
In our experience the 845 tube is very reliable and can
last for several years of regular use. Similarly with the
6SL7. If the sound deteriorates after approximately
2000hrs (2 years @ 3hr per day) but the amplifier
appears to be working OK suspect the 6SN7.
Generally speaking valve failure may be one of these:
1, The valve continues to work but the emission gets
low. In the case of 845 output valves this will result in
not being able to set the bias properly.
2, The valve gets noisy/microphonic. Usually happens
to the small valves, can be confirmed by tapping gently
with a plastic 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 re-
commencing 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.
5, Changing valves:
Before changing the 845 valves ensure that it safe to do
so by switching off and removing the mains plug at least
20 minutes before hand. This will enable dangerous
voltages to dissipate, and the valves to cool down.
If possible check the bias setting before you attempt to
change the valve(s), in order to familiarise yourself with
the procedure.
If changing both the 845s 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. Note that only 845 valves
*See engineers notes at rear
are compatible with the amplifier, 805, 211 and
similar looking tubes cannot be biased and may
damage the amplifier, and could be dangerous.
6, If you cannot set the pointer in the black section,
then the valve is probably faulty or is unsuitable. (If
both valves read zero the HT fuse may have 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
845, 6SL7, 6SN7 or equivalent. 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. It's just 'plug and play'. (These valves are
similar with the same pin connection; accidentally
interchanging these two valves would not cause
damage, buy will reduce the amplifier performance).
6SN7 should only be replaced with modern types.
Vintage types and the Russian 6H30 type have lower
ratings and are unlikely to work well.
Icon Audio is happy to check the valves/amp or re-
bias your amp free of charge.
8 Specification & Features
(Typical conditions @ 240v 50Hz)
•
845 output valves
•
6SL7 double triodes for first stage
•
6SN7 double triodes for 2
•
Hand wired point to point components
•
No printed circuit board or
•
PTFE valve bases for low noise/leakage
•
100w RMS at clipping (28.3v @8 Ohms)
•
100w RMS at clipping (20v @4 Ohms)
•
Signal to noise level -95db
•
Freq response 20Hz-20kHz +or- 0.5db
•
Power bandwidth -3db=20Hz-30kHz 90w
•
0.01% THD typical 8w (0.015% 1w) 1khz
•
Custom hand wound transformers using
Japanese long grain steel
•
Supplied with attractive safety guard
•
Minimal feedback used 6db (high) 12db (low)
•
High quality oversized metal film resistors
•
Audiophile High quality polypropylene or Jensen
audio capacitors (optional upgrade)
•
Internal wiring using silver audio cable
•
Valves carefully matched for best performance
•
Gold plated Input & speaker terminals
•
400 mv sensitivity for full output (High)
•
1v sensitivity for full output (Low)
•
230/240volts, 200watts (zero signal)
•
5 amp (10 amp 115V)T mains rear fuse (with
spare)
•
250 ma T 845 anode fuses (with spares)
•
W: 20cm. D: 50cm. H: 22cm. Weight:35kg
•
IEC mains lead, (5amp fused UK only)
•
CE certified. ROHS & WEEE compliant
Specification subject to change without notice.
nd
stage
Page 9
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