Part 7 - Chassis wiring guide I

By now, you should have a chassis with almost everything in place: both transformers, four valve sockets and all front and rear panel controls. You also have a turret board with 23 wires sprouting from its turrets. Don't rush to start soldering up the turret board connections just yet.


Adding the EL84 heater wiring

For many valve amp builders, adding the valve heater wiring is one of the most fiddly and tiresome jobs. The best time to add it is when there's nothing else in your way, so get it done BEFORE making the turret board connections. (You may find it easier to temporarily remove the turret board so that its wires aren't in the way.)
      Start by soldering 35cm of green wire to each of the '0' and '6.3V' lugs on the 'Sec2' winding of the power transformer. Add 35cm of black wire to the 'CT' lug. Now twist these three wires together and run the bundle towards the back panel of the chassis, then along the chassis edge and then across to the V4 valve socket. These wires connect as follows: black to pin 3, one green to pin 4 and the other to pin 5. Trim them to length and attach them to these pins, but do not solder them just yet.
      Take two more pieces of green wire (each approx 15cm long) and attach them to the pins 4 and 5; now solder these two pins (making sure that there are no wire whiskers shorting them together or to neighbouring pins). Take 10cm of yellow wire and attach it to pin 3 (where the black wire is attached). Now you can solder this pin, too.
      Pull this yellow wire out of the way - in the general diection of the V3 socket (you will solder it at a later stage). Now take the two green wires you have soldered to V4 and twist them together. Run this pair to the chassis back panel again, along and then forwards to the V3 valve socket. Trimming them to length, attach one wire to pin 4 and the other to pin 5. Before soldering them, attach another pair of green wires (each approx 18cm long) - one to each pin. Solder these two pins. This completes the EL84 heater wiring.


Add three wires to the Sec2 winding of the power transformer and connect them to the valve sockets


Twist the heater wires to keep them together, but don't worry if the twists aren't super-tight: it's neither tone- nor noise-critical


Take your time - getting two wires into a single valve socket pin isn't a job to rush! Good light and patience are the key to success



Adding the ECC83 heater wiring

You have a pair of green wires sprouting from the V3 valve socket; twist them together, run them to the back of the chassis and along the chassis and then forward to the V2 socket. This is for an ECC83 valve, which has a different heater setup. Start by trimming them to length; attaching one of these green wires to pin 9 of V2. Then attach the other to BOTH pin 4 and pin 5. One way to do this is to strip the insulation to expose around 1cm of the wire - this will be long enough to pass through pin 4 and then back through pin 5. Don't solder these wires just yet.
      Add the final two green wires (each 16cm long) to pins 4 and 9 of V2. Now solder these two pins. Twist these wires together and run them to the back panel of the chassis, along it and then forward to the V1 socket. One wire connects to pin 9 of V1 and the other connects to BOTH pins 4 and 5 of V1. Trim them to length and solder them in place to complete the valve heater wiring. Now that you've completed the wiring of all four valve heaters, your chassis should look something like this (below).


For both of V1 and V2, pins 4 and 5 are connected together: strip a little extra wire and use it to make the connection




Input jack socket (J1) wiring

Many people get confused by the 4 solder lugs on Marshall-style jack sockets, and which lugs make the various connections to the rest of the amp circuit. The PP-18's hotter input (J2) is also wired a little differently than most amps. This guide and the input socket pictures and diagrams on the right should make it crystal clear. For extra clarity, the photos are taken with the socket outside the chassis. In fact, it's virtually impossible to solder to the input sockets if they're mounted inside the chassis, so why not temporarily mount them on the outside of the chassis (right)?
      The first step is to take the 'hotter' input jack socket, J2, and use one of the two unused 1M resistors (R2), to connect lugs 1, 2 & 4, as shown in this first photo (above right). One of the resistor's leads passes through lug 4 and diagonally back to lug 2; the other end connects only to lug 1. Don't solder any of the lugs yet.
      Now take ??cm of shielded wire supplied with your kit and strip one end of it, so that you have a short length of shield (twist it to make a single wire) and the separate centre conductor. The two are still insulated from each other. Attach the centre conductor to lug 1 of the socket and the shield to lug 4, as shown in the second photo (middle right).
      Now take the 'normal' input jack socket, J1, and use the other 1M resistor, R1, to connect across lugs 1 and 4. This time, however, omit the diagonal connection from lug 4 to lug 2. Add ??cm of shielded wire to this socket, in exactly the same way that you did for J2.
      Now fit the two sockets to the front panel so that you can complete their wiring. Use a short piece of the uninsulated wire to run from lug 4 and 3 on J1 to lug 4 on J2. Use another short piece of the uninsulated wire to connect lug 2 on J1 to lug 1 on J2. Solder all except lug 2 of J2.
      Move the input sockets back into the chassis and refit the turret board to the six M3 mounting points on the chassis. Find the black wire that runs from C1 on the turret board and trim and solder it to lug 2 of J2. It seems a lot more complicated than it is - the picture (bottom right) shows all of the connections with annotations.


The resistor on J2 - the 'Hot' input - connects three of the four lugs together


The shielded wire - with shield and central conductor separated - connects to two of the solder lugs


You may find it much easier to make the connections with the input sockets temporarily fitted to the outside of the chassis - just be careful not to damage the plexi panel!


This diagram shows the full set of connections for the two input sockets. When this stage is complete, the two shielded wires are left unconnected at one end - you'll complete this wiring in the next stage.


Initial V1 connections

Your turret board is in place, and you're now ready to start adding the wires to the valve sockets. There are three wires that run from the turret board to V1: two yellow and two red. The Wiring guide diagram shows your turret board connections. Start by trimming and soldering the two yellow wires to pins 3 and 8. The red wire connects to pin 6 and then pin 1. The simplest approach is to add a short loop of connecting wire from pin 6 to pin 1, as shown in the first photo on the right. Solder these two pins.       Next solder one end of R3, the 56k resistor, to pin 2 of the V1 socket. Take the other end of the resistor and wrap it around the top of the top-left turret on the turret board (leave the hole in the turret top for the moment). Now take the shielded cable that comes from the J2 input socket and bring it over to this same turret. Trim the cable to length and then strip it to reveal the centre conductor. Cut off and discard the exposed copper shield (not needed, because this wire is already grounded via the input socket), and use some heatshrink to insulate the end of the shield. Attach and solder the centre conductor to the top of this same turret.
      Finally, take the other shielded wire (from the J1 input socket) and prepare it in the same way: solder it to pin 7 of the V1 socket. Your V1 socket should look like the one shown bottom right.


There are two yellow wires and one red wire connecting the turret board to the V1 valve socket


The R3 resistor connects directly between the valve socket and one of the turrets


With the shielded wires from the input sockets added, V1 should now look like this

  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