Trace Elliot PT

[lowell]

I had to replace a PT on a SMX GP12. Got this from British Audio. British Audio Service & Music

It came without the usual wiring diagram or color code on the side. And the lead colors do not match what's in the amp. I found the 2 primaries with my meter, there is no internal connection between them.

Can someone please let me know if my drawing is correct? Safety being priority #1 ...then 120v/220 switching.

[Jazz P Bass]

That wiring diagram appears to me to be for 220Vac input. (series wired coils)

For 110Vac input you would want to wire the two coils in parallel.
Not too sure how this can be accomplished with the switch as shown (DPST)

[lowell]

There's a switch in the diagram. Switches between series/parallel primaries.

[catalin gramada]

you need to have care with transformers wich have multiple windings. The conection of the sections should be done in the same direction the wiring was turn. You have to add not to substract so is important to know the begining of each winding

[Jazz P Bass]

That switch is NOT drawn correctly.

There should be two 'wipers'.

220 Vac : Connect Blu/ Brn

110Vac: connect Gry/ Brn & Blu/ Purp.

[lowell]

They emailed me that Grey/Brown are Live and Blue/Purple are Neutral. Hoping they were correct.

JPB. It's a DPDT switch. Am I missing something or you? and it's wired exactly as in your second post.

[lowell]

Here I've drawn the contacts in 120vac position.

Sorry if my image is confusing.

[Enzo]

I think the confusion is that in your first drawing, the diagonal link on the switch LOOKED like a switch throw. You did not draw in any moving contacts. it is much clearer since you added them.

[lowell]

Yep I thought that was the problem. Thanks.

[Mick Bailey]

Last week a customer dropped in one of these amps he'd recently bought - it was dead and had been blowing fuses. He said he'd installed a brand-new mains transformer because an electrician had told him the old one was blown, but it still does the same.

When I inspected the amp it was a disaster - a ball of electrical tape surrounding two screw connector blocks and a neutral wire poking out of the tape. The new transformer had the wires cut off and joined onto the original wiring so it was all pulling bowstring-tight. This amp didn't have a voltage selector fitted, but I could see a purple and grey lead soldered to the back of the mains switch, paralleled onto the brown/blue (L&N).

So, the first think I did was to remove all of the mains wiring and start from scratch. It immediately became clear that the original amp was wired for 110v. Our mains is 240v. The guy had just wired the amp up the same as it had come to him, without considering what the original fault was. For 220v brown is live, neutral blue and the purple/grey are connected together, placing both windings in series. To double-check I bought up the transformer (disconnected from the amp) on the variac and monitored the current draw, then checked the secondary voltages.

There's an interesting thing with some TE amps in that they sometimes only use one of the primary windings for 110v operation and leave the other disconnected.

[Simon Richards]

I just rewired a 150w gp7 transformer for 110v: blue & violet to live, grey & brown to neutral, and so far so good.

Simon Richards