Engineers Notes - icon Audio Stereo 845 User Manual

Engineers Notes

These notes are only intended for use by an engineer
qualified to work with high voltage triodes like the
845/805. Owners should refer any problems to a
dealer, service agent or Icon Audio depending upon
area purchased in.
The amplifier may be inverted by supporting the
transformers on non abrasive surface (e.g. dense
foam, books etc) which allows space between the
845s and the work surface.
Safety
Before removing base disconnect the power cord.
Always allow 10 minutes for the HT to discharge, or
measure before proceeding. Use a bleed resistor of
around 5-10KΩ will speed this up, and check that the
HT voltage has discharged.
Amplifier dead.
Check the 20mm mains fuse in the IEC socket at rear
of the amplifier, if dead there is a spare included. Or
the fuse in the plug (if applicable). If not either check
in-line power switch fuse adjacent to IEC socket.
Amplifier lit but not working.
There is a 250ma HT fuse located on the chassis,
with spares attached to the base. If the fuse blows
again a VARIAC will be useful to operate the
amplifier on reduced voltage in order the trace the
fault or overload.
Make sure the bias for the 845s is correct. If the AC
fuse is blowing with the HT fuse disconnected
suspect the bridge rectifier or power supply.
Also check that the 6SL7/6SN7 6.3v supply is
working.
230v to 115v Conversion.
Take the precautions as above. It is necessary to
change the primary power windings from series to
parallel. Remove either AC lead from the bridge
rectifier and join it to the other terminal. The "centre"
tap are the two leads that will be found joined
together. Replace with these two and solder to the
first terminal. A larger value AC fuse will be needed in
the IEC socket.
115v to 230v Conversion.
This is changing the two primary windings to series.
Remove either pair of AC leads from an AC input to
the bridge rectifier. Join together and insulate. The
other pair of AC leads should be separated and
soldered to each AC input of the bridge rectifier. A
lower value AC fuse will be needed in the IEC socket.
The incorporation of a built in bias meter for easier
checking of the bias current of the 845 output valves.
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*See engineers notes at rear