Unclear About This Illuminated Rocker Switch

[cpsmusic]

Hi,

I have an illuminated rocker switch that was removed from the power supply of a tube guitar amp. The switch was acting as the main power switch and has three connections.

The switch was wired as follows - the AC input connected to the middle contact (2), while the outside contacts were connected to (1) ground and (3) the rest of the power supply circuit.

When I was looking at this in the circuit I thought it was odd as I expected one switch position to connect contacts (1) and (2) which would have shorted the mains to the chassis!

Now that the switch has been removed from the circuit I've checked it and there doesn't seem to be a position that connects contact 1 to either of the other two contacts. From what I can see the switch is SPST. Anyone know anything about switches like this one?

Cheers,

Chris

[helius]

The key word is "illuminated". There is a neon bulb between "ground" (should be neutral but old equipment was wired unsafely) and the parallel switch contact. When the switch is operated, it acts like a DPST internally with the second pole connecting live to the neon bulb. Neon bulbs look like infinite resistance until the voltage across them reaches 90V.

[floobydust]

Maybe check your pin numbering or the connections 1 and 3 flipped.  Illuminated AC switches are wired like this inside.

[Brumby]

While the form factor might strongly hint and at a SPDT switch - it is only a SPST, as you have determined.  What it will have is (more than likely) a small neon lamp with a series resistor connected between pins 1 and 3.

When power (pin 2) is switched to pin 3, both the supply circuit and the neon are powered - the neon needing an earth/neutral point for completing the circuit.

Edit: Typo

[cpsmusic]

While the form factor might strongly hint and a SPDT switch - it is only a SPST, as you have determined.  What it will have is (more than likely) a small neon lamp with a series resistor connected between pins 1 and 3.

When power (pin 2) is switched to pin 3, both the supply circuit and the neon are powered - the neon needing an earth/neutral point for completing the circuit.

Thanks, that makes sense.