Variac wiring

You can see from the remains of the original connection wires.

The supply goes to the top two terminals, (2) and (4).

The output uses the centre terminal at the bottom (3) and the common terminal at the top (4)

This will allow you to alter the voltage to your lights from zero to normal supply voltage.

Nope. One of your wires will be coming from the supply and needs to be connected to (2) The other will be going to the lamp and needs to be connected to (3).

Unfortunately you also need a third wire, from the other terminal of the lamp, to go to (4).

You can get a different type of dimmer that only has two wires going to it but a Variac needs three wires to give a full range of control.

see from the remains of the original connection wires.

I see, that makes sense. I guess I will have to find an alternative solution that will not use the ligh switch box, as regular dimmers create noise in the audio signal. Thanks very much for the clarification.

Just an aside:

The "standard" variacs permit producing up to 140 volts to the load and also permitted "up" to be either clockwise or anti-clockwise.

Do you suppose connecting the Variac as a variable inductance in series with the load would provide enough range? Not the best solution, but one that could be done with only the two wires available. Anybody ever tried this?

Roby

That thought was why I wrote "from zero to normal supply voltage".

There are three options:

1) Connect to (3) and (4), leaving (2) unconnected. The control will vary from full to dim very quickly, with only a very small part of the winding in circuit. At that point there will be 100v over this part of the winding and several hundred volts over the complete winding, as the VARIAC will operate as an off-load step-up transformer. Not exactly recommended.

Better:

2) Connect to (2) and (4) and place a dummy load between (3) and (4). If the lamp load is the same wattage as the dummy load, the Variac will give half to full power adjustment. 3) Connect to (3) and (4) and place a dummy load between (2) and (4). If the lamp load is the same wattage as the dummy load, the Variac will give from zero to half power adjustment.

By combining (2) and (3) above, using a change over switch, full power range can be achieved.

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I can see the dummy load if the variac is used in series but what is the point of using a series connection in the first place? The dummy load destroys the whole reason reason for a variac rather than a rheostat- efficiency. It is so much simpler to simply hook it up as intended (which is what you originally said Input on 2 and 4 , output on 3 and 4. Full control is possible with a simpler setup. It is assumed that it is being used within its rating.

I agree entirely - which was why I didn't suggest this to the OP. But the question was specifically asked by another poster and someone might have tried it. They may not have thought of the autotransformer implications - tt is far more dangerous than using a rheostat, unless the dummy load is there and always connected.

Agree.

The OP started off by thinking they could use this variac auto transformer in the same way as a typical wall switch mounted 'dimmer'.

Two wire connection at the wall switch!

Not so.

Then it got complicated by suggesting using it as variable inductance in series with the lighting circuit.

The OP had enough sense to ask an intelligent question; but some of the suggestions are beyond a reasonable purview of someone not wanting to rewire part of their installation/building.

--------- Too true. Thanks for the response.