Part 4 - Chassis assembly



This page shows how to use the pre-punched chassis (shown above) that comes with the Time saver version of the PP-18. If you bought the Basic version of the kit, you will have your own chassis, so use these pictures and instructions as a general guide.


Power transformer

The outside of the pre-punched chassis is covered with a protective plastic film; peel it off before you start. Then fit the power transformer - it mounts through the large rectangular cut-out that's surrounded by four M4 screw holes. Undo the four nuts and remove the fixing hardware from the underside of the transformer: one shakeproof washer, one plain steel washer and then the red fibre washer. Mount the transformer on the chassis' top surface, sliding the solder lugs through the rectangular hole.
      The power transformer can go either way around, but it's probably best to have the mains-related solder lugs (0-120 and 0-120) closer to the front of the chassis. This will help you make neater cable runs. With this transformer in place, refit all of the fixing hardware in the same order. So, the red fibre washer will be against the chassis, then the plain steel washer fits on top of that, then the shakeproof washer and finally the nut. Tighten the four nuts fully.

The PT mounts through the large rectangular hole on the chassis; use its own M4 hardware


Output transformer

The output transformer runs across the chassis (from front to back), and is almost in the centre. It mounts using two of the three 4mm holes (the two that are shown circled red in the picture below).


      Use M4 screws, shakeproof washers and nuts, and turn the transformer so that its solder lugs are facing towards the power transformer. Then fit a rubber grommet into the 10mm hole that's just to the side of the output transformer, close to these lugs.

Use M4 hardware to secure the output transformer, and add the rubber grommet to the hole next to the transformer


Valve sockets

The pre-punched chassis has five valve socket holes (numbered 1-5 in the photo, right). The PP-18 uses four of these for the ECC83 and EL84 valves. Add the first pair of 9-pin valve sockets to positions 1 and 2. These are preamp valves, so use the valve shield bases to secure the ceramic socket; rotate the socket so that the gap between pins 1 and 9 is towards the front of the chassis. Use M2.5 screws and nuts with M3 shakeproof washers to secure these bases.
      The sockets for the two EL84s go in positions 4 and 5. Use the EL84 retaining clips to secure these sockets to the chassis. Use the same combination of hardware to fix the clip and socket. Then fit the black hole cover to the final socket hole (position 3).




The PP-18 uses four socket holes: 1 and 2 for the ECC83s; 4 and 5 for the EL84s


Orientate all sockets so the gap between pins 1 and 9 is towards the chassis' front


The EL84 spring clips are a useful reminder of which valve fits into which socket


Front panel controls

There are two pots (variable resistors), two switches, a neon indicator and two jack sockets to mount on the front of the chassis. They mount through your kit's gold-coloured plexi control panel and hold the panel in place.
      Start by adding the outer components - the neon indicator and the input jack sockets. There's a small amount of tolerance so use this to line the other hole positions up before tightening the nuts up fully. Then add the other controls:
* Power switch - orientate the switch vertically in the chassis
* Standby switch - so that the two solder lugs are closest to the open side of the chassis
* Pots - so that the solder lugs are towards the open side of the chassis, but just rotated very slightly (see Mounting the pots, right for extra details)
* Knobs - with the pots fitted and tightened, fit the chickenhead knobs. To do this, first rotate the pots' shafts so that it's at minimum (anti-clockwise). Place the knob on the shaft and aim the head of the knob at '0' (zero) on the control panel dial. Fix it in position by tightening each knob's set screw.

Mounting the pots

The pots supplied with the PP-18 have nylon shafts that are already cut to length, so there's no preparation required. Each has a serrated locking washer and a nut. The serrated washer goes on the inside of the chassis and the nut on the outside. When you secure the pots in place, it's worth rotating them very slightly off-centre (see above) so that adding the tone control components is easier later on.


Rear panel parts

Fix the rear control panel into place by using M2.5 hardware for the small hole at one end and the IEC socket (with its two countersunk M3 screws) at the other end. Use the slight tolerance to line up the other three holes before fully tightening these nuts.
      Add the two speaker sockets, so that the solder lugs face the open side of the chassis. Add the fuseholder (which already has its fuse installed); it has a D-profile hole for anti-rotation, so can only be fitted in one position.


The fuseholder has a D-profile and can only be inserted one way round


Solder lugs for grounding

There are four 4mm holes for grounding lugs placed around the chassis (shown with red circles in the photo, right). The first position is close to the IEC socket. Use an M4 screw, shakeproof washer and nut to fix a solder lug in place here, bending the 'arm' of the lug upwards (shown right) - to make easy access when you later add the wiring.
      The second grounding lug goes in the hole close to the 8-ohm speaker socket, the third is close to the Input socket and the fourth is close to the Power switch.
      Now your chassis will look like this (below), and it's time to move on to the turret board. Double check that all controls are in place and aligned as described above before proceeding.


Use M4 hardware to add four solder lugs around the chassis perimeter


Bend the arm of each lug so that its hole is accessible for soldering


  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