WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
Building, troubleshooting and testing of these amplifiers should only be
performed by someone who is thoroughly familiar with
the safety precautions around high voltages.
Sowter http://www.sowter.co.uk/ are very good. I would say he is the top UK manufacturer. The performance is the best possible using EI construction.
Have a browse of his web site, and, if you don't see exactly what you want, send him an e-mail. He will probably answer personally, and is always helpful.
He does not normally charge extra for "specials".
Keepings all parameters constant, how significant is the core achitecture? How would a C core compare against an E-I and a toroid? Toroids seem to offer a lot, but precious few make their way into output transformers.
I have no personal comparitive experience with C core or torroids as OPT, and can only speculate:
The core "grain" runs in the same direction as the magnetic field. Perhaps that is why the power to weight ratio is better on C core and torroids
When used as power transformers, C cores have no electrical disadvantages over E-I (they just cost more), but torroids do have slightly poorer regulation for a given VA rating. I wonder if that would equate to damping factor in OPT's?
It must be very difficult to sectionalise torroid windings - or maybe it's not so necessary as there will be fewer turns and the electrostatic properties of the core are so different to iron.
Is it feasable to "gap" torroids for SE, or does the torroid's field just collape?
among us Munich Triode Mafiosi it seems to be common sense to prefer Lundahl to Sowter if Lundahl is providing a trannie meeting the requirements. Sowter trnnies always were second winners in direct comparisons.
Vinylsavor reported the Tango XE-20S to be comfortablly better than the Lundahl 1664-SE. But this is SE. It looks like Lundahls core/winding topology is better suited for PP. Allen Wright reported that the Lundahl LL1663-PP outperformed his fancy Tamura trannie.
So on my ongoining PP tube amp project, i intend to compare my Tango XE-45-5 and a Lundahl LL1663-PP. Output tubes are AD1, comparable to 2A3. I keep you informed as soon as it happens.
I had the opportunity to listen in when at AES 107 in New York, when Menno van der Veen and Bill Perkins 1st met face-to-face. Both these guys know ALOT about transformers - at 1st it was a mutual respect gushing and then these 2 got down to talking about the relative merits of C cores and torroids -- it got way over my head ... but EI trafos seemed to be considered an also ran. The gist, like everything else in hi-fi, was that execution plays at least as important a role as topology.
It is also interesting to note, that both these guys are PP kinda guys...