Version 1.32
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transformer terminal B1 can now be soldered but be careful not to heat the tags for
prolonged periods as they are plastic and can melt.
For clarity when looking at the output transformer, on the secondary winding side you
will see three pins, two are closer together and one is slightly further away. The one
slightly further away is the 0 ohm tapping, the middle is the 4 ohm tapping and the pin
closer to that is the 8 ohm tapping. Generally it is 0 --- 4 - 8 (see note at end)
A ground wire should also be connected between X12 on the right PCB to the earth
tag on the chassis. There should now be three wires to the earth tag; the main earth
from the inlet socket, the earth to point X17 on the power supply board, and the earth
to the right PCB. If they are all present then the earth tag can be soldered. This is
where you add the 22 ohm resistors. Two 22 ohm resistors are soldered in parallel,
one end joins to the earth tag on the chassis along with the main wire from the inlet
socket and the other two wires from the earth of the psu board and the earth from the
earth from the audio board join to the top of the 22 ohm resistors. This helps to reduce
hum.
To connect the heaters, link the two yellow wires from the mains transformer to
points X7 and X8 on the right PCB, the polarity does not matter. Now link points X7
and X8 on the right PCB to points X7 and X8 on the left PCB respectively, the
polarity of this connection is important to stop the heater windings from shorting if
both the earths are connected on the PCBs. If using two mains transformers from the
plus kit, connect the two yellow wires from each of the transformers to points 7 and
X8. Do not now use the bridging link between the two supplies.
To wire the EL34 heaters on the left PCB, the grey pair of wires from the mains toroid
are connected to pins 2 and 7 on V2. Then, two wires from pins 2 and 7 on V2 are
connected to pins 2 and 7 respectively on V1. For the right PCB the mauve pair of
wires are used and connected in the same way. The 54R9 resistors are used across the
EL34 heaters to reduce hum. Take a pair of 54R9 resistors and twist one end together
and solder to form a v-shape. The non joined ends are solder in parallel with the
heater wires to pins 2 and 7. The joined end is then connected to X12 via a wire link.
Do this for all 4 of the EL34 tubes. This forms a hum bucking circuit to reduce ac
mains generated hum.
The transformer windings that are not used should be cut off and/or insulated using
the heat shrink so that none of the windings are touching (they may be useful one
day). Do not join any of these windings together.
