Anybody ever strap the secondarys of PTs

[skyboltone]

I got gobs of transformers that provide the right voltage but about 2/3rds the power I want. I've never tried it but on the AC side of the rectifier, could a guy just tie both center taps down and parallel the ousides of the HT windings?

The transformers are identical. I think if you parallel the rectified side you just double the voltage.

[Structo]

Interesting Dan, you should give it a go.

On my Hammond amp that is now a 6V6 Rocket I added a tube so now I have three 12ax7's and the two 6V6. 5U4 rectifier.

I remember you said that these PT's are soft and you weren't kidding.
I think adding that third tube pulled the B+ voltage down by around 50v.

Now there is 292v on the 6V6 plates.

[Jana]

You can pair up a set of identical power transformers. Just make sure that you have the phase correct on all the windings--if you don't the transformers will get hot very fast and you will lose the magic smoke.

[skyboltone]

You can pair up a set of identical power transformers. Just make sure that you have the phase correct on all the windings--if you don't the transformers will get hot very fast and you will lose the magic smoke.

Those were precisely my thoughs Jana. These are Heyboers so I imagine there's a lot of smoke in there.

Now, checking polarity. Scope, yeah, that's the ticket. There's a way to do it with a Simpson and a flashlight battery too but I would have to fool with it to figure it out.

Thanks
Dan

[marcoloco961]

You can pair up a set of identical power transformers. Just make sure that you have the phase correct on all the windings--if you don't the transformers will get hot very fast and you will lose the magic smoke.

Those were precisely my thoughs Jana. These are Heyboers so I imagine there's a lot of smoke in there.

Now, checking polarity. Scope, yeah, that's the ticket. There's a way to do it with a Simpson and a flashlight battery too but I would have to fool with it to figure it out.

Thanks
Dan

I'd be interested on hearing about the Simpson and flashlight battery test. I have no Scope, but often wonder how to determine polarity on the Transformers.

[skyboltone]

You can pair I'd be interested on hearing about the Simpson and flashlight battery test. I have no Scope, but often wonder how to determine polarity on the Transformers.

I think, if I remember correctly it goes something like mark one of the HT leads with a little tape or something to tell the difference between the two right? They are usually both red. Then hook up your Simpson with the neg lead on the marked one and the pos lead on the other. Then you juke the primary with a quick tap of the black lead on the positive and the white lead on the negative of the battery. Just tap it. And then reverse the battery and juke the winding again. On one of those two directions the meter needle will take a quick bump backwards and the other way with the battery it will jump forward. So because the primary leads are identified white and black you can determine polarity of the secondary based on which way makes the needle go + and which makes it go minus when the black lead is tapped on the positive. Mark both transformers the same. Be sure to account for the turns ratio when you set the scale on the meter. It's been a really long time but that's sort of what I think happens. Maybe.

Warning, Warning. Keep your hands off the stripped part of the black lead when you are doing your juking. The collapsing field can swing a pretty good hammer.

[Wayne]

You could do it with a multimeter and household AC, too.

Choose ONE lead from each secondary (ignore the CT). Connect them together.

Power each primary normally from the wall/suicide cord/whatever.

Measure the AC voltage between the two unconnected secondary. It'll either be twice the voltage of a single secondary, or it'll be near zero.

If it's near zero, you have the right leads connected together. If it's 2x the secondary voltage, you've got them backwards.

Before doing this, make sure your meter can handle 2x secondary voltage.

W

[skyboltone]

Wayne; This ain't clear so I'm going to edit it just a tiny bit for you. I don't think mine is all that clear maybe either so feel free.

You could do it with a multimeter and household AC, too.

Choose ONE Ht Lead lead from each transformer (ignore the CT). Connect them together.

Power both transformer primarys normally from the wall/suicide cord/whatever. Blacks together, whites together.

Measure the AC voltage between the two unconnected secondary wires; one from each transformer. It'll either be twice the AC voltage of a single secondary, or it'll be near zero.

If it's near zero, you have the right leads connected together. If it's 2x the secondary voltage, you've got them backwards. Do this for each secondar (6.3, 5 VAC) if you plan to strap everything.
You could use your variac to narrow the hazards a bit

Before doing this, make sure your meter can handle 2x secondary voltage.

This is a simple and elligent procedure Wayne, I like it

W

You have to visualize what you are doing here. On one half of the cycle 0-180 degrees the voltage will swing positive on both coils if you have the right leads. The other side of the coil will be energized on the second 180 degrees of the AC cycle. Don't miss understand what Wayne is saying here and connect the HT leads from one transformer together. You won't like the way that turns out.
Nice job Wayne.You are trying for zero across one lead from each transformer.

[Wayne]

It made perfect sense to me at the time, but I can see where I left lots of places for ambiguity to creep in. Thanks for plugging those up for me! The idea is sound - my description of it wasn't

W