OT magnetic field

[eddie25]

I seem to remember a diagram showing the general direction of the magnetic field around a working output transformer, but I can't seem to find it again. Something like a figure 8 type pattern. Am I crazy, or can someone clue me in about this and how it might relate to OT placement?

[xtian]

The magnetic field generated by the PT is what you have to worry about, because it can induce hum in your OT. Heard of the headphone trick? Helps you find the exact placement of the two transformers in relation to each other.

[eddie25]

Yeah, I get what you are saying. I am more thinking along the lines of if you have the OT on the input side of the amp away from the PT. Getting it to be least likely to cause problems with the preamp section. Or in this case is it just purely proximity and not orientation?

[LeftyStrat]

As I understand it, the fields run parallel to the lams. This is why you'll notice most PT's are mounted with the lams parallel to the side, in line with the power input and power switch.

It would make sense, whether the OT is near the PT or not, to mount it at 90 degrees to the OT. Having the lams of the OT pointing towards the input I would imagine would more likely lead to interaction.

But I'm no expert on the subject. I follow having the PT lams parallel to the side, and use the headphone trick to place the OT.

[tubeswell]

The direction of the laminations is a guide. Generally you want the OT lams to be 90 degrees to the PT lams, if they are in the same 'plane', in order to prevent electromagnetic induction from one to the other. What helps even more, is if you have a z-mount PT and an x-mount OT - then the laminations will be assured to be out-of-synch.

[JazzGuitarGimp]

Yeah, I get what you are saying. I am more thinking along the lines of if you have the OT on the input side of the amp away from the PT. Getting it to be least likely to cause problems with the preamp section. Or in this case is it just purely proximity and not orientation?

I've wondered about the same thing. My guess is, the preamp tubes are more sensitive to electrostatic fields than magnetic fields. But I certainly am not an authority on the subject. I'm just trying to learn as I go.