Part 8 - Chassis wiring guide II


By this stage, you have the preamp valve (V1) and guitar input jack sockets fully wired up (see Part 7). Now move on to add the wiring to the phase inverter (V2), power valves (V3 and V4) and the Volume and Tone controls.


Phase inverter (V2) wiring

The V2 valve socket is even easier than V1 to wire up. There are six wires - two yellow, two red and two blue - to connect. Make sure to connect each wire to the correct pin (see the Wiring diagram for a reminder of the destination for these wires). Before moving on to solder the two power valve sockets, check the connections you've made so far. Every pin on V1 and V2 should now have a connection.




Wiring the power valves, V3 and V4

In contrast to V1 and V2, some of the pins for the power valves are unused. They're quite quick to do. Start by connecting the two blue wires from the turret board: one goes to pin 2 of V3, the other to pin 2 of V4. These wires supply the in-phase and out-of-phase signals from the phase inverter to the power valves.
      Now attach the yellow cathode wire to pin 3 of V3. Before soldering this pin, take the yellow wire that you previously soldered to V4: trim it and add it to pin 3 of V3 and solder this pin. Next, connect the red wire from R17 to pin 9 of V3. The two valves share this screen resistor, so before soldering this pin, add a short red wire to connect it to pin 9 of V4.
      Finally, there's a red and a white wire to complete the EL84 wiring, The white wire goes to pin 7 of V3 and the red wire to pin 7 of V4. That completes the valve socket wiring, and your V3 and V4 sockets should look like those shown right.


Some of the pins on the EL84 sockets are left unused, but you must have connections on pins 2, 3, 4, 5, 7, and 9


Wiring the front panel controls

There are three wires (two blue, one black) that run from the turret board to the Volume (VR1) and Tone (VR2) controls on the front panel. When you connect them, you also add capacitors C3 and C4. Start by trimming and stripping the wires so that they connect to the three lugs of the Volume pot - but don't solder them yet.
      For both C3 and C4 you need four short pieces of PVC (about 1-2cm each) to use as insulation. You can use PVC insulation from some of your unused blue wire; carefully remove all of the strands of wire so that you're left with little pieces of empty PVC tube. Slip two pieces over each end of the leads of C3 and C4 (see right).
      Now use C3 to connect from lug 1 of VR1 to lug 1 of VR2. The blue insulation makes sure that C3's leads cannot short against the pot's metal body or the chassis. Do the same to connect C4 from lug 3 of VR1 to lug 3 of VR2. Then directly connect lug 2 of VR1 to lug 2 of VR2 with a piece of blue wire. Solder all six lugs - including the wires from the turret board. The result should look like the photo on the right.


Make some PVC insulation from some short lengths of unused blue wire


The slight rotation of the pots from vertical makes it easier to add the three connections


Standby switch and grounding

In the centre of the chassis, you have two red wires that run towards the front of the chassis, from the turrets at D1+D2 and C12+R20. Run these over to the Standby switch (S2) and trim them to length. Solder one wire to one of the switch's lugs, and the other to the switch's other lug (it doesn't matter which way around they are).
      You also have two black wires running from the turret board. The one that's running from C12 grounds the power amp circuit; trim and solder it to the ground lug close to the Standby switch (see top right).
      The other black wire, running from C10, grounds the preamp circuit. Trim and solder it to the grounding lug near the input sockets (right). At this point, your chassis will look like the photo below, with all of the wires that run from the turret board soldered into place. If you have a wire left unconnected, retrace your steps and correct your mistake before continuing to the next stage.


After wiring the Standby switch, add the black grounding wire that's close-by


The preamp ground connection is the last of the existing turret board wires


  PP-18 construction guide
  1 - Kit contents
  2 - Block diagram
  3 - Reading your schematic
  4 - Chassis assembly
  5 - Turret board assembly
  6 - Turret board wiring
  7 - Chassis wiring guide I
  8 - Chassis wiring guide II
  9 - Chassis wiring guide III
  10 - Initial testing
  11 - Final test

  Main diagrams:
  Schematic
  Input wiring
  Control wiring
  Turret board layout
  Turret board wiring
  Test-point diagram
  Final chassis picture

  PP-18 kit purchase page

  PP-18 construction guide
  1 - Kit contents
  2 - Block diagram
  3 - Reading your schematic
  4 - Chassis assembly
  5 - Turret board assembly
  6 - Turret board wiring
  7 - Chassis wiring guide I
  8 - Chassis wiring guide II
  9 - Chassis wiring guide III
  10 - Initial testing
  11 - Final test

  Main diagrams:
  Schematic
  Input wiring
  Control wiring
  Turret board layout
  Turret board wiring
  Test-point diagram
  Final chassis picture

  PP-18 kit purchase page