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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 or service agent.
The amplifier may be inverted by supporting the
transformers on non abrasive surface (e.g. dense
foam, books etc) which allows space between the
805s and the work surface.
Safety
Before removing base disconnect the power cord.
Allow 20 minutes for the HT to discharge.
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).
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 or variable transformer will be
useful to operate the amplifier on reduced power in
order the trace the fault or overload.
Make sure the bias for the 805s is correct. If the AC
fuse is blowing with the HT fuse disconnected
suspect the bridge rectifier or power supply.
230v to 120v 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.
120v 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.
*See engineers notes at rear
Page 10
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