I have built a fair number of tube amps and always used EI OPTs. I seen that Antek sells toroidal OPTs, both SE and PP.
Do they work as well as EI OPTs?
Do they work as well as EI OPTs?
Tube amplifiers exist for more than 100 years now, and AFAIK nothing definitive emerged yet. You mention EI and toroidal, but also C-Core and R-core can be evaluated. And then a plethora of core materials, and of winding setups for each of these transformer types...
A toroidal transformer is a "better" transformer than an EI, in that it is more efficient, more broadband by nature. That can be used to good advantage in a PP OPT (even toroidal for mains applications have been used as broadband OPTs). For SE toroidals can be used, but the advantages are less pronounced.
A toroidal transformer is a "better" transformer than an EI, in that it is more efficient, more broadband by nature. That can be used to good advantage in a PP OPT (even toroidal for mains applications have been used as broadband OPTs). For SE toroidals can be used, but the advantages are less pronounced.
I've used some toroidal output transformers from two manufacturers, both SE and PP. Results have never been remarkably bad, neither have they given me reason to vouch for them. The push-pull transformers from the Polish firm Toroidy have been surprisingly free of any bad resonances, I'll give them that. I've also tried one of their SE transformers, and that wasn't bad either, though not as completely free of resonances as their PP variants I'd measured.
An earlier toroidal I've tried was a Finnish push-pull build from Trafox. Wound on a smaller core it was a perfectly usable transformer with a wide-ish bandwidth, but sadly it was somewhat lacking in the bass department. Driven by a pair of EL34's it couldn't manage more than 5 watts at 30Hz before saturation. Other than that, it did sound brilliant, though.
An earlier toroidal I've tried was a Finnish push-pull build from Trafox. Wound on a smaller core it was a perfectly usable transformer with a wide-ish bandwidth, but sadly it was somewhat lacking in the bass department. Driven by a pair of EL34's it couldn't manage more than 5 watts at 30Hz before saturation. Other than that, it did sound brilliant, though.
It depends, it depends, it depends. The performance is relative to how the secondary and primary were wound. Does it have sufficient inductance for the lowest frequency of interest? Minimized stray capacitance and leakage inductance?
The A Number One problem to watch out for is DC core magnetization, which is worse with torroidal OPTs. EI cores have some small air gaps that limits DC core magnetization. When using torroidal OPTs, it's best to include separate bias current setting pots so that the Q-Point bias currents can be equalized.
For Push Pull, an R-Core would be the ideal choice
http://softone.a.la9.jp/english/
The benefit of a toroid is lost once you cut it for an air gapped se output. I don't see how they can cost effectively wind them any better than a toriodal power transformer which have a poor stack.
http://softone.a.la9.jp/english/
The benefit of a toroid is lost once you cut it for an air gapped se output. I don't see how they can cost effectively wind them any better than a toriodal power transformer which have a poor stack.
A little DC unbalance in th two halves of the primary can quickly magnetize the core of a toroidal XFMR to saturation. If you are careful to avoid that, then the toroidal output XFMR can turn in superlative performance.
I have a pair of Amplimo toroidal transformers from the Netherlands. What concerns me in the case of the toroidal transformers is their intolerance of DC imbalance, which will be worse than for an E-I based transformer. Toroidal transformer are by their nature gapless, which will show up any DC imbalance pretty quickly.