To help ensure that everything goes together without a hitch,
it's a good idea to read the following information in its entirety before
reaching for your soldering iron!
Referring to the overlay diagram in Fig.1, begin by installing
all the wire links. There are 15 links in total, 11 of which must be formed from
1mm tinned copper wire. Use 0.7mm wire for the remaining four links. The overlay
diagram shows the larger (1mm) links in red.
Set aside all of the heatsink-mounted transistors (Q4-Q17), the
two 470μF electrolytic
capacitors, choke (L1) and 6.3mm spade lugs for the moment. We'll deal with
these in more detail shortly. All other components can now be installed,
progressing from smallest to largest.
The 1W and 5W resistors should be mounted about 1mm proud of
the PC board to aid heat dissipation. Also, be sure to orient the cathode
(banded) ends of diodes D1-D5 as shown.
When installing the fuse clips, note that the small retaining
lug on each clip must be positioned to the outer (fuse end) side, otherwise fuse
installation will be impossible.
If you intend mounting the output transistors horizontally,
then it's also necessary to install 3-pin header strips in the mounting
positions for Q8 & Q9. As we'll see shortly, these are required because the
transistor leads are too short to extend all the way through the PC board
Fig.1: use this diagram when assembling and wiring the amplifier module. The ±70V wiring is routed underneath the board and attached to it with cable ties once testing is complete.
DANGER: HIGH VOLTAGE!
The 140V DC supply across the filter capacitor bank and the amplifier supply rails is potentially lethal! After the power supply wiring is complete and before you apply power, mount a clear Perspex sheet over the capacitor bank to protect against inadvertent contact - now or in the future! Note that the capacitors take some time to discharge after the power is switched off.