I have a Hammond 374BX power transformer and a Triad C-14X choke, and was wondering it there are any issues mounting the choke directly below the PT inside the chassis (for the Simple SE)? From what I can tell, the axis of the choke winding is vertical, whereas the Hammond winding axis is horizontal (I think), so my understanding is that they shouldn't have massive coupling. But is this a bad idea in general? Has anyone else tried this?
Is the power transformer on top of a metal chassis while the choke is underneath it? If so, then there is likely to be negligible coupling between the two magnetics. If you have access to an AC voltmeter with a 1 or 2 volt AC range on it, you could place the meter across the choke's 2 wires, power up the power transformer, and see if there's any voltage showing up across the choke; if it's only a few millivolts, then I would not worry about it. Rotating the choke wrt the transformer might let you find a null spot, and you could mount the choke that way, if practical to do so.
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Yes, they will be separated by an aluminum chassis with the choke underneath.
I've seen other comments about how to test for hum, but being relatively inexperienced with all of this, how exactly do you power up the power transformer? Do I need to have the whole amp assembled, or do I just need to have the mains of the PT wired up? And do I just tape off all the other PT wires?
I've seen other comments about how to test for hum, but being relatively inexperienced with all of this, how exactly do you power up the power transformer? Do I need to have the whole amp assembled, or do I just need to have the mains of the PT wired up? And do I just tape off all the other PT wires?
I have done exactly as you are describing on both my 3C24 amps as well as a pair of 300B amps I'm working on currently.
The 3C24s have a pair of the Triad chokes you are using in a choke input mounted to the PT's mounting bolts. You are correct in the orientation of the coils I believe. The 300Bs is a capacitor input PS with one choke on the top of the amp and the other will be below under the PT but in a different orientation.
It found it VERY easy to determine the best orientation. Get a pair of wired earbuds and either use an adaptor or solder on a pair of alligator clips. Clip those leads to the choke leads (or the OPT) Insulate all the secondary wires on the PT. Hook up the primary to the mains carefully. With the PT oriented as in the chassis listen to the choke as you move it into position and find the quietest position. You do the same with the OPT and find the quietest position.
The 3C24s have a pair of the Triad chokes you are using in a choke input mounted to the PT's mounting bolts. You are correct in the orientation of the coils I believe. The 300Bs is a capacitor input PS with one choke on the top of the amp and the other will be below under the PT but in a different orientation.
It found it VERY easy to determine the best orientation. Get a pair of wired earbuds and either use an adaptor or solder on a pair of alligator clips. Clip those leads to the choke leads (or the OPT) Insulate all the secondary wires on the PT. Hook up the primary to the mains carefully. With the PT oriented as in the chassis listen to the choke as you move it into position and find the quietest position. You do the same with the OPT and find the quietest position.
You could try the experiment with just the transformer (xfmr) itself powered up. Keep in mind that when the xfmr is under load, it will radiate a stronger magnetic field. I guses is that if you find a null position with no load, that will be the best position for the loaded xfmr as well.
Even with minimal direct magnetic coupling, placing these components close to each other can still lead to electromagnetic interference. The PT can generate significant electromagnetic fields. All components must be well shielded.
Shielding against electric fields is straightforward; an aluminum foil shield can work just fine. Time varying magnetic fields will be only very slightly affected by an Al shield, likely because they may cause eddy currents in the foil. Magnetic fields are difficult to control, and high permeability iron alloy shields are needed for that. Best way is to prevent the problem by spacing the magnetics far enough apart to prevent the coupling, as you suggest.
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