Ty,
I built a nice little Simple SE from tubelab.com (picture below) with Transcendar transformers. I am quite pleased by the excellent sound of these transformers. They are very good and have excellent bass as well as excellent response across the audio band.
I also have a set of Electraprint transformers that I ordered from Jack for a 300B amplifier that I am in the process of designing. Just for grins I hooked them up to the Simple SE and they sound fantastic too. I noticed slightly more bass with the Electraprint. I'll have to listen to them more to give a more detailed commentary, but they are no doubt excellent transformers. They will be in the 300B amplifier in the near future.
As an aside, an e-mail I got from Jack when I was ordering the transformers from him noted that the 300B transformers he built for me were similar to 25 Hz filament transformers. I thought that was an interesting comment.
I don't think you would go wrong with either transformer.
As for the James units, I have some of them (6112's) as well in my G*S*G and they are quite good. I doubt that they have as much iron in them as the Transcendars simply due to their size. I don't think they are intrinsically better than the Transcendars, an opinion based on subjective evaluation obtained when swapping amps around, which I do frequently. Transformers when you get right down to it are simple devices, however, there are many ways to design them. Whether one method of construction is better than another I don't know. I think we would need to measure them all and take the subjectiveness out of the evaluation. I haven't measured any of the transformers I have to determine which is better. All I know is that all the above transformers sound very good and are more than adequate for quite good listening experiences.
Frankly, in most situations, I think the speakers you use are the most important part of the system. Transformer differences, are for the most part, small enough when you're into this level of performance to not matter as much as the speakers IMHO.
FWIW, the speakers I use most of the time are Zaph ZRT's that I built (
www.zaphaudio.com) from John Krutke's plans published on his Web site. They are excellent for what they cost to build. The drivers used in John's design are some of the best available in terms of response and distortion characteristics. John is an absolute expert in speaker design and is highly regarded. These are amazing speakers. Here's a picture of the ZRT's I built:
EDIT: By the way, Madisound has kits for these speakers. Wish they had had the pre-routed baffles when I built mine. I had to cut my own holes. Anyway, here's the link:
http://www.madisound.com/catalog/produc ... ts_id=8591
Have a great week!