All the toroids listed, and including the Antrim line, from Ireland and made under licence around the world, seem to be fine. From reports of all these toroids, it would appear there are few bad toroids around, and I have also used Chinese toroids which seem quite good as well.
One issue with toroids can be DC-induced hum. All mains supplies, and particularly in the states where a biphase transformer is used for light/power, suffer a small amount of DC on the line, typically 300mV. Toroids, because of their high magnetic flux densities (typically 1.5 tesla), are susceptible to DC, which sets a small DC current and skews the B/I S-shaped curve to one side of zero. This can take one half cycle (depending on the direction of the DC current through the primary) into saturation, and this almost always makes an irritating buzz. EIs are not so sensitive to this, but then EIs have high radiation at low currents, so it's swings and roundabouts (as always!!).
There is a circuit, originating in Russia I believe, which uses a strapped bridge rectifier to eliminate the DC current, and this scotches it. But it adds expense and complexity, of course, and offsets the space/cost advantages of a toroid.
Cheers,
Hugh
