DPST Power Switch Configuration

[namore17]

Hello,
First post here and have kind of a newbie question. Making some changes to an old epiphone valve jr. amp project where I'm building out a cabinet to turn it into a combo. I was planning to add a faceplate, and to simplify drilling the faceplate was planning to change out the current power switch to a fender carling DPST switch. based on the current configuration of the power switch, I'm a bit confused how I should setup the new power switch.

I put together a diagram to help try to sort out how the new switch should be soldered, but was hoping someone might help me confirm the setup and maybe give an explanation on how the hot and netural wires on the switch are interacting with the power transformer?

My assumption (configuration 1 on the drawing) on the new switch was the hot + 117v PT wire should be going to one side of the switch (top gold lugs) and neutral + 0v PT wire to the other set of lugs (bottom silver lugs)?

Thanks to anyone that can help me sort this out so I don't destroy the power transformer.

[martin manning]

The switch function should be as shown, Valve Jr schematic attached. You should be able to work it out from there...

[romberg]

You can use the continuity checker (or ohm setting) on your DMM to quickly test and confirm which lugs on your new switch do what. Your switch should be two switches in the same package. This means that two of the lugs should never show continuity (or zero ohms) to the other two in both the on and off positions. First find the two pairs that never connect to the other two. Then each isolated pair will connect each other when the switch is on. Shout out if this is not clear.

Since this is switching mains voltage you want to be 100% certain what exactly your new switch does before wiring it up.

On the original configuration, the neutral is not switched at all. They just use the switch lug as a place to join the two wires. The switch does nothing for the neutral side of the AC line. The hot side is switched. You can do the same on the new switch or switch the neutral as well (this is what I would do).

I would also get and install a fuse before the switch. The hot lead should run directly from the IEC inlet to say a 1 to 3 amp slow blow fuse and then from the fuse to the switch. Maybe your IEC inlet already has a fuse built into it? If so then you don't need another.

Mike

[namore17]

Thanks for the tip Mike to measure continuity, I think all of that makes sense to me. I would want a pair that is showing continuity to have a hot connection each. And then same for neutral on the other side?

The only piece that is a little concerning or confusing with the setup on the power transformer is it looks like there may not be a 0v wire, so I'm not sure I actually can join anything to the neutral. The original picture included the PT, but its a tad hard to see. I attached a clearer picture.

There is a fuse built into the inlet so all good there.

-Nick

[martin manning]

The black leads are the primary. The polarity doesn't matter, so you can call either one 0V, and the other 117V.

[namore17]

Got it, good to know, thank you!

So then if I have my info right, I want to have to have the switch closing the connection between one of the black wires and the hot and neutral wires simultaneously (since this is like 2 switches in 1).

[martin manning]

That’s it.

[namore17]

Thanks all for your help! Will double check the continuity tomorrow and hook it up to try it out.

-Nick