Transformer Orientation

[C Moore]

I am re-using this amp chassis. It was a PA head originally. Can I have 2 lay down transformers like this. I thought the lams had to be arranged at 90 degrees to each other.?
Thank You

[Dingleberry]

I've been taught that way too, but I've also beel told that in a P-P amp it's not always the case. I think that the thing is when you inject two signals that are out of phase into the P-P OT, it actually cancels out the hum that could be induced to from PT magnetic fields. The 90 degree orientation is only for minimizing exess hum as far as I know. Now when I think that with my common sense it actually makes sense. I think some of the gurus can verify my conclusion.

-T

[Phil_S]

I think it is not really the lams, it is the coils. In this case, it appears they are at 90 degrees. Without looking inside, I can't be certain, but it certainly appears that way based on how the end bells look.

[Alexo]

If it doesn't induce hum, then yes, it can work.

[C Moore]

I think it is not really the lams, it is the coils. In this case, it appears they are at 90 degrees. Without looking inside, I can't be certain, but it certainly appears that way based on how the end bells look.

OK, my mistake.
If we look at a different view, it does show the windings are at 90 degrees.
Thanks

[Cliff Schecht]

Yeah that's fine, they are at 90 degrees from each other. This setup is super common in old PA's like Bogen's.

[C Moore]

Yeah that's fine, they are at 90 degrees from each other. This setup is super common in old PA's like Bogen's.

Thanks Cliff -
I'm sorry, but one more time, just to verify....
Ultimately, it is the Windings that need to be at 90 degrees, not the Lams.?
Thank You

[Phil_S]

The lams and the colis are integrated, so I think we are splitting hairs. The lams take the shape of an "EI" without the gap. The coil goes around the middle finger of the E. The topology of a laydown (Z mount) transformer is different than a standup. With standup (x mount) transformers it is very easy to say, put them at right angles and it seems obvious what to do. With z mount transformers, it isn't so obvious, so I suggested looking at the coils.

Consider this, it is the middle finger of the E on which you judge whether you've got them at right angles. The problem, though, is people will tire quickly of the middle finger.

Mind teaser: one x mount and one z mount and then what?

[C Moore]

The Baltimore Colts....
OK Phil, points well made. I appreciate the education and the humor....
Thank You

[Alexo]

Does no one else use the headphone trick?

You can argue about how many angels can dance on the head of a pin all day, but there's no substitute for cramming a bunch on there and watching how many fall off.

[C Moore]

I do not know what the head phone trick is.

[Alexo]

I do not know what the head phone trick is.

You hook the PT up to the mains (very carefully - insulate any loose leads and use a switched power strip for an extra level of safety, turning it on last) and hook the OT secondary into a pair of headphones.

You can hear the hum come and go through the phones as you experiment with different transformer orientations. 90 degrees is a good rule of thumb, but the optimum placement seems to be different with every set of transformers, in respect to both distance between them and their orientation. I've had some that really wanted to be 75 degrees to each other, looked like an accident/drunk drilling, but it was what the electrons wanted. You just never know.

If you can get it to be pretty quiet in the phones, odds are it will be dead silent through a cab. You can also hook the OT secondary to a speaker or a cab to double check, but the phones are more sensitive.

You can do this on a scope too, and some people prefer it, but to me, there's nothing like hearing what's going on.

...again, be very careful - especially if it's a scratch build and the PT is not bolted down and has all those leads sticking out of it. Lotsa wire nuts & one hand behind the back!

[C Moore]

I do not know what the head phone trick is.

You hook the PT up to the mains (very carefully - insulate any loose leads and use a switched power strip for an extra level of safety, turning it on last) and hook the OT secondary into a pair of headphones.

You can hear the hum come and go through the phones as you experiment with different transformer orientations. 90 degrees is a good rule of thumb, but the optimum placement seems to be different with every set of transformers, in respect to both distance between them and their orientation. I've had some that really wanted to be 75 degrees to each other, looked like an accident/drunk drilling, but it was what the electrons wanted. You just never know.

If you can get it to be pretty quiet in the phones, odds are it will be dead silent through a cab. You can also hook the OT secondary to a speaker or a cab to double check, but the phones are more sensitive.

You can do this on a scope too, and some people prefer it, but to me, there's nothing like hearing what's going on.

...again, be very careful - especially if it's a scratch build and the PT is not bolted down and has all those leads sticking out of it. Lotsa wire nuts & one hand behind the back!

Sorry about this, but I must be missing a few steps some where. Are you talking about a PT and OT that are free standing, not hooked up to anything.?
What is in between the two transformers.?
I am not sure about using head phones, do they have an impedance that is close to a regular speaker.?
Thanks

[overtone]

it does seem strange at first, but in the headphone procedure there is no connection between the PT and OT. They are just "floating".
There is no power connection to the OT so there is no need to load it.
I have done this just with headphones and also with a dummy load that has a headphone out, used standard headphones and 600ohm ones which perhaps were quieter. Both ways work fine and it is a quick very worthwhile test.
The "hum" is quite low volume so you have to listen carefully,

best, tony