Transformer primaries

[Bugman3183]

Good afternoon.   This will be my first time using a transformer with multiple hook up options for the primaries and I wasn't 100% sure on how to wire it for 120v operation. Figured I'd let the experts guide me rather than taking a chance on burning something up.   Any advice would be greatly appreciated.   Thanks.

[sluckey]

I don't think anyone can explain it any better than the pdf you posted.

[Bugman3183]

I guess.....  seems simple, but I've only built a couple of amps and the other transformers I've used looked more like the one I've attached here.   No chances of messing that up for sure, but this one looks like you would have to hook up four wires just for the primaries and that just seems counterintuitive to me. I certainly would rather not damage this very expensive pt hooking it up the way I "think" it should go when there's a whole community of nice folks here who know better than i.  Also, having smoked a pt in the past, I may just be overly cautious.

[pompeiisneaks]

I guess.....  seems simple, but I've only built a couple of amps and the other transformers I've used looked more like the one I've attached here.   No chances of messing that up for sure, but this one looks like you would have to hook up four wires just for the primaries and that just seems counterintuitive to me. I certainly would rather not damage this very expensive pt hooking it up the way I "think" it should go when there's a whole community of nice folks here who know better than i.  Also, having smoked a pt in the past, I may just be overly cautious.

In a nutshell, to provide support for two input voltages, they have two identical windings that you connect either in series or paralell depending on which voltage you need.  If you need 120V do as the top picture shows and connect in parallel
if you need 240V use the lower and connect in series.

does that help?

~Phil

[Bugman3183]

Yes it does, thank you.   That confirms what I thought, but I definitely wanted confirmation because I certainly don't have 130 bucks to replace this one if I was wrong. Once again, maybe overly cautious.   Thanks.

[sluckey]

You posted two different transformer diagrams. Which one do you actually have?

[Bugman3183]

I have the first one posted.   I posted the second one as an example of something along the lines of what I have seen in the couple amps that I've built so far.  It's been confirmed that i was on the right track, so all is well.

[PRR]

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[sluckey]

Twist the BLK/WHT and BRN/WHT wires together and connect to the white wire in your power cord. Twist the BLK and BRN wires together and connect to the power switch.

[dscottguitars]

Twist the BLK/WHT and BRN/WHT wires together and connect to the white wire in your power cord. Twist the BLK and BRN wires together and connect to the power switch.

Does it matter that the blk/wht & brn/wht are connected to the neutral side of power cord? I'm not sure I paid attention to that in the past. I see a black dot on the plain wires in the drawing; is that for the hot side?

[sluckey]

Twist the BLK/WHT and BRN/WHT wires together and connect to the white wire in your power cord. Twist the BLK and BRN wires together and connect to the power switch.

Does it matter that the blk/wht & brn/wht are connected to the neutral side of power cord? I'm not sure I paid attention to that in the past. I see a black dot on the plain wires in the drawing; is that for the hot side?

It really doesn't matter. I simply chose to connect the /WHTs to the white neutral as a convention just to kinda follow NEC code (which has no jurisdiction inside an amp). If there had only been one Black and one white primary wire I would have connected the white to neutral.

The dots are phase dots. They don't indicate hot side.

[92Volts]

Does it matter that the blk/wht & brn/wht are connected to the neutral side of power cord? I'm not sure I paid attention to that in the past. I see a black dot on the plain wires in the drawing; is that for the hot side?

They're phase dots which aren't usually needed for a power transformer. They confirm black & brown go to one polarity while blk/wht & brn/wht go to the opposite.

Not "necessary" here because the diagram shows how to connect the wires, but it's the same notation used anywhere else you need to know phase... like OPTs where phase matters for feedback purposes but the transformer company can't predict or show you which hookup is correct in your particular circuit.

[dscottguitars]

Thanks for the info.

92Volts, if I may ask one more question about your comment about the phase dots on an OT. I've often wondered how to know which secondary goes to which tube. Most of the time I get lucky. Is is there a way to know which tube to connect it to? Out of the PI I know there is the standard signal from the #1 pin, and the inverted signal from the #6 pin. But I don't know which primary the dot goes to.