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SE-5a Chassis wiring - part 1


By now, you should have a chassis with almost everything in place: both transformers, a pair of valve sockets and all front and rear panel controls. You also have a turret board with 21 wires sprouting from its turrets. Start by fitting the turret board in place using six M3 shakeproof washers and nuts.

Adding the valve heater wiring

You have two long lengths of green wire running from one corner of the turret board. Twist them together and run them towards the back panel of the chassis, along the chassis edge and then across to the V2 valve socket. These wires connect to pins 4 and 5 of this socket. Trim them to length and attach them to these pins, but do not solder them yet.
      Take two more pieces of green wire (each approx 20cm long) and attach them to the same pair of pins. Now you can solder pins 4 and 5 on V2 (making sure that there are no wire whiskers shorting them together or to neighbouring pins).
      Twist this second pair of green wires together and run them to the back panel of the chassis, along the back and then across to the V1 socket. Attach one of these green wires to pin 9 of V1, and 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. Now solder these pins.


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


When you've completed the wiring of the valve heaters, your chassis should look something like this


Input jack socket (J1) wiring

Many people get confused by the 4 solder lugs on jack sockets, and figuring out which to use for the connections to the rest of the amplifier. This guide and the input socket pictures on the right should make it crystal clear (for clarity, these photos are taken with the socket outside the chassis). The first step is to use the 1M resistor (R1) that remains unused from your kit contents, to connect lugs 1, 2 & 4, as shown in this first photo. Note: one of the resistor's leads passes through lug 4 and passes back diagonally to attach to lug 2. The other end is connected only to lug 1. Don't solder any of the lugs yet.
      Now take about 17cm of the shielded wire supplied with your kit and strip one end of it, so that you have a short length of shield (twisted together to make a single wire) and the separate centre conductor. The two are still insulated from each other. Solder the centre conductor to lug 1 of the socket and the shield to lug 4, as shown in the second photo (right).
      Finally, take the black lead that is connected to C1 and R3 on the turret board and trim it to length and strip its end so that you can attach it to lug 2 of the socket. Solder this wire to complete the socket wiring; it should look like the socket shown in the third photo (right). Note: there is nothing to solder on lug 3 of the socket.





Initial V1 connections

There are four wires that run from the turret board to V1: two red and two yellow. The Wiring guide diagram shows your turret board connections. Trim each of these four wires and solder it into position.
      Now take the shielded cable that comes from the input socket and bring it over to the V1 socket. Trim the cable to length and then strip it to reveal the centre conductor. Cut off and discard all of the exposed copper shield (this wire is already grounded at the input jack), and use some of the heatshrink to insulate the end. Attach and solder the centre conductor to pin 2 of the V1 socket.
      Note that pin 7 of the V1 socket does not have a connection yet - you'll add it later. Your V1 socket should look like the one shown right.


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


The central conductor of the shielded wire connects to pin 2 of V1

V2 connections

There are now four wires to connect from the turret board to V2:
* blue to pin 2
* yellow to pin 3
* brown to pin 7
* red to pin 9
That completes all wiring for the V2 socket. It should look like the one shown right.


The wiring for V2 is complete; EL84 valves do not use pins 1, 6 or 8

Standby switch (S2) wiring

In the centre of the chassis, you have two red wires that run from the turrets at D1+D2 and C11+R16. 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.


The Standby switch is simple: one wire for each lug, and it doesn't matter which way around you attach them

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