Inductor placement

[ducati guy]

I'm planning a power amp with four inductors; power transformer, power supply choke, output trans and plate choke. With only 3 mutually perpendicular axes, there is no way to avoid having the coil of one parallel to that of one other. Based on some measurements I've made, it seems that coupling between the output transformer and plate choke would be least troublesome. Reasonable conclusion? 

[Grainger49]

Try some at a 45 degree angle.  That would limit the coupling.  But distance works best.  Magnetic fields diminish with the square of the radius.

[Paul Joppa]

You mean, like the SEX amp? Where plate choke and output transformer are mounted bottom to bottom with the same mounting screws? Obviously I think that's reasonable!

Remember you can put use units that are parallel if they are well spaced. That's how the Paramount is configured, with plate choke on one side of the power transformer and output on the other side.

Symmetry counts as much as orientation, and the 3-D fields are sometimes not what you think they are. I usually just put a voltmeter across the higher-impedance winding while the power transformer is energized, to actually measure the induced voltage as I move a transformer around to find the best location or orientation.

[ducati guy]

I've breadboarded the amp with everything spaced widely and probed around with a second output transformer connected to my multimeter to get an idea of what is interacting with what. I like the long, thin look of the Cary SET amps and am trying to build one with a similar appearance. Everything is in a straight line down the middle of the amp except for the power supply choke at right angles to the power transformer, so distance is my friend. I can put the output transformer behind the power transformenr (further away from plate choke but close to the mains inlet) or behind the power tube (closer to the plate choke). I'll probably have to make one of each to see if their is a difference, but was hoping not to have to get so extreme.

[Grainger49]

You mean, like the SEX amp? Where plate choke and output transformer are mounted bottom to bottom with the same mounting screws? Obviously I think that's reasonable!

Remember you can put use units that are parallel if they are well spaced. That's how the Paramount is configured, with plate choke on one side of the power transformer and output on the other side.

Symmetry counts as much as orientation, and the 3-D fields are sometimes not what you think they are. I usually just put a voltmeter across the higher-impedance winding while the power transformer is energized, to actually measure the induced voltage as I move a transformer around to find the best location or orientation.

I think this is logical, pragmatic and genius!

[ducati guy]

I would have to agree. I've spent much time studying my Paramounts and other Bottlehead amps for things you can't pick up from books.