The Amplifier Power Supply Unit

Part A - The Mains Side

The first circuit diagram shows the circuitry from the mains (power) entry through to the A.C. supply to the transformers. This is essentially the design outlined in G3SEK's control design. Two terminal blocks have been added to enable the amplifier to be changed between 120v and 240v mains (line) supply easily.

Click on a component to see a photograph!

The DXpedition Amplifier Mains-side circuitry

The key parts of the above circuit are:

• The 3-minute delayed start +12v relay, K101, switched directly from the control card.
  

• The step-start circuitry. This places a 47 ohm resistor in series with the mains supply for a couple of seconds after power is supplied to the HT transformer via K101 to limit current inrush. Take a look at a simulation of the the step-start circuit. R103a and R103b are placed in series (making 2k ohm) for 240v mains operation and just R103b is used (1k ohm) for 120v mains operation. Use link 5 for 240v and link 6 for 120v.
  

• The 120V / 240v switching via the two terminal blocks (one 6-way and one 4-way (photo only shows 4-way block)

The outputs are in the form of AC1 to AC8 provides mains (line) power to the HT and LT transformers.

Parts List