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SE-5a Chassis wiring - part 3


Output transformer - secondary

Start by soldering the wires to the output transformer's secondary winding - the lower row of four solder lugs for the speaker connections. Tip: when soldering wires to this bottom row of lugs on the output transformer, you may find it easier to temporarily dismount it from the chassis.
      First, solder about 20cm of orange wire to the 0 lug (the lug on the right of the row of four). Then solder 20 cm of green wire to the 8-ohm lug and 20cm of grey wire to the 16-ohm lug. Twist all three wires together and thread them through the rubber grommet.



With the wires soldered to the output transformer, remount it on the chassis (if necessary), twist the wires together and poke them through the rubber grommet

Output transformer - primary

It's important to remember that when the amp is running, the top row of lugs on the output transformer carry a very high DC voltage - the only part of the amp outside the chassis that does. So this set of lugs must be properly insulated against accidental touch. Using the insulating sleeve and heatshrink can be fiddly, but it's a necessary safety precaution.
      First, attach 20cm of brown wire to the left lug, and then add 20cm of red wire to the right lug (ignore the central lug in this row). Solder and insulate these wires as shown in Insulating sleeves, right). Then twist the two wires together and push the wires through the rubber grommet. The fully wired-up transformer will look like the one shown below.




Insulating sleeves
When soldering to the top row of lugs on the output transformer, don't make a fat ball of solder. Keep the joint small, so that there will be room for the heatshrink and the insulating sleeve will be able to slide over it (below).


Slide an 8mm piece of heatshrink up each wire and over the soldered joint. Apply heat so that the tubing shrinks around the joint (below). Add an 8mm piece of heatshrink to the unused centre lug, and apply heat to insulate that lug, too.
Now slide each wire through the appropriate hole in the insulating sleeve (making sure you have it the right way round!). Finally, slide the insulating sleeve up to cover the row of solder lugs.



Speaker socket wiring

There are just a few 'loose ends' left. First, complete the speaker output wiring. Inside the chassis, take the twisted bundle of wires (orange, green and grey) from the output transformer's secondary and run it to the back of the chassis and then across to the speaker sockets, J2 (16-ohm) and J3 (8-ohm). Trim and solder the grey wire to lug 1 of J2, and the green wire to lug 1 of J3. Trim and connect the orange wire to lug 3 or 4 of either socket, but don't solder it yet.
      Use a piece of the uninsulated solid-core wire to run through lugs 3 and 4 of both sockets. Solder some black wire to the grounding lug that's close to the 8-ohm socket and then connect the other end of this wire to lug 3 of J3. Now solder lugs 3 and 4 on both sockets. The speaker socket wiring should now look like the photo on the right.


Add a short bus wire to lugs 3 and 4 of the speaker sockets when you add the wires from the output transformer

Final turret board connections

The final connections for your SE-5a are three bundles of wire connecting from the transformers to the turret board. First, take the red and brown wires that come through the rubber grommet from the output transformer and run them over to the turret board. Connect them to the two turrets between C10 and C11, as shown in the photo opposite.
      Now solder two 20cm lengths of green wire to the 0V and 6.3V solder lugs on the power transformer's 'Sec2' winding. Twist these wires together and run them over towards the the turret board. Next, solder 20cm of brown wire to each of the 190V lugs on the power transformer's 'Sec1' winding and 20cm of yellow wire to its 0V lug. Twist these wires together and run them over towards the turret board. Use another cable tie to keep these two bundles of wire - green+green and brown+yellow+brown together (see second photo on the right).
      The green+green wires connect to the two vacant turret tops at R11 and R12 on the board. Trim each wire and solder one to each turret. Similarly, the brown+yellow+brown wires connect to the other three empty turret tops:
* a brown wire to D1
* the other brown wire to D2
* the yellow wire to the empty turret next to C11
      Add the final two cable ties to keep these bundles of transformer wires neatly organised.


Connect the brown and red wires from the output transformer to the top of the turrets in the centre of the turret board


Add five wires for the secondary windings and run them over to the turret board; use a cable tie to keep the wires together...


... and then connect them to the vacant turret tops near the edge of the turret board

Get ready for testing!

This completes the wiring. Your completed chassis wiring should look like the image below. Before you power up your amplifier, it's vitally important that you test your chassis wiring and soldering work (see next section).

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