Output Transformer Placement

[irishpatrick33]

Question:

I am assembling a stereo tube amplifier. Can I put (2) GXSE15-8K output transformers literally stacked on top of each other on opposite sides of a chassis skin without creating flux interference? Said another way, I would like to mount OT's to the same spot on the chassis in a mirrored (opposing) configuration. Or perhaps less desirably, could I mount these opposing... but then rotate one 90 degrees horizontally (so bobbins face different directions)?

For instance, the guy in this video seems to have mounted PT's exactly as I just mentioned: YouTube

From what I gather, I would induce hum if I put OT's side by side where bobbins parallel each other and point in same direction. Again, I read there'll be issues even if I put them side by side with one bobbin turned 90 degrees, in a perpendicular configuration. Side by side is bad, from what I gather. So the opposed mounting is a thought to minimize footprint and hum. The power transformer is a toroidal and will not be a factor. Thoughts?

 

[BJosephs]

The hum he is demonstrating isn’t coming from the two OT’s proximity to one another, it’s coming from the choke that he is manipulating near them. OT’s can induce signal on one another but the signal won’t be hum unless you put hum through one of them. If the PT and chokes are far from the OT’s you will be safe with putting them in almost any orientation except with the bobbins facing each other. I prefer having them be parallel to one another with some distance between, but the mounting plane doesn’t really matter.

 

[merlin el mago]

"except with the bobbins facing each other"

Why?

 

[BJosephs]

"except with the bobbins facing each other"

Why?

Because that is where the magnetic fields are. But maybe it’s ok with signal transformers. The best thing to do if you are unsure is to copy what other people have been successful doing.

 

[merlin el mago]

As inductors for passive xover?

 

[BJosephs]

As inductors for passive xover?

I’m no expert. Just leveraging what I know about my own projects and the detail presented in OP’s video

 

[irishpatrick33]

I've got more questions now, especially after seeing that graphic. Does number 8 refer to literally stacking ei transformers on top of each other? That was one of my ideas.

Does that graphic refer to toroidal transformers with the doughnuts? I was under the impression I didn't have to worry about toroidal placements. In fact, I was considering stacking a toroidal choke under the toroidal power transformer. Issue?

 

[merlin el mago]

I've got more questions now, especially after seeing that graphic. Does number 8 refer to literally stacking ei transformers on top of each other? That was one of my ideas.

Does that graphic refer to toroidal transformers with the doughnuts? I was under the impression I didn't have to worry about toroidal placements. In fact, I was considering stacking a toroidal choke under the toroidal power transformer. Issue?

No, the pic is refering to xover inductors.

 

[BJosephs]

I've got more questions now, especially after seeing that graphic. Does number 8 refer to literally stacking ei transformers on top of each other? That was one of my ideas.

Does that graphic refer to toroidal transformers with the doughnuts? I was under the impression I didn't have to worry about toroidal placements. In fact, I was considering stacking a toroidal choke under the toroidal power transformer. Issue?

That graphic shows inductors wound on a round bobbin. These are not like a toroidal transformer. For one, the winding directions are different between the two (toroidal transformers have the winding wrapped around the band, going from ID to OD with each turn, whereas these inductors are typically wound around the outside circumference). Second, toroidal transformer placement is less critical because the secondary winding is wrapped around the inner primary. It’s due to the shielding behavior, not the shape, that makes the transformer less magnetically reactive to its neighbors.

 

[irishpatrick33]

So I am at the more advanced stage of designing a spud amplifier. The chassis is a wider left to right. The board will go on the left or right end. Which makes more sense? Should I have the PT/choke next to board, or OT's next to board?

Like so:

Board | PT/choke | OT's
or
Board |OT's | PT/choke

Also, what are desired distances between said components?



Thanks

 

[AllenB]

Example. Put the power transformer on one side. Then the choke and early supply filter. Then put the output stage supply filter by the output transformers, then the output stage. Then the input stage supply filter and the input stage.

 

[irishpatrick33]

It sounds like you are saying the tube pcb should be on one end, power transformer on other end, with output transformers between the two.

Board | OT’s | PT/choke

 

[AllenB]

Yes, keep the low level signal parts away from the noisy end. Mount the power transformer in a direction that keeps the board clean, and the output transformers in a direction that doesn't pick up the supply.