SY said:
You can do a pretty good job of reverse-engineering something, but the reality is that modern materials and better tooling can make a better transformer. The more I work with new transformers, the less enamored I am of the vintage iron in my collection.
And in many cases you will need to modify an old design because some of the materials used in the old design are no longer available.
So---- nothing beats having a collection of the original blueprints--- where you can compare and contrast a design amongst it's brethen from the same company--- and thereby learn the logic of the design and the design principles behind the number of turns, wire size, core size and etc.
because if you have to change any one of these--- that change will itself produce a host of other electrical and\or mechanical changes in the subject transformer. And then not knowing the logic and wu of the design milieu of the particular series--- you'll just be grasping at straws when you make changes--- and the design loses it's original integrity.
I don't want to (and won't) go too much into detail of how vintage designs can bee and must bee optimized if made today--- for (unfortunately) obvious reasons.
My experience with guys who have tore down tranneys is first and foremost the teardowns have rarely if ever been accurate nor complete. And since they did not have an uderstanding of the design precepts of the unit they were tearing down--- they have frequently really been at a loss as to what to do---- or how to make sense of the data they have. Again--- that is where having the entire range of the family of designs really becomes advantageous.
And lastly think of the motivation that most tear down artists have in mind. Not knowledge for the beauty and the aesthetic of understanding a design--- but a moreso practical reason--- they want a cheap knockoff. If your motivation is to do it cheaper--- the intracacies and subtleties of a design are just likely to go way over your head. These same subtleties and intracacies (even if accidentally discovered) are likely to be sacrificed in the building of the knockoff because, again, the motivation here is to make it cheaper and make it profitable to build.
When I first started out--- back in 88 or 89---- I did not envision myself winding transformers---- I got some blueprints and then sent them out to different transformer houses for quotes. Invariably--- I would get a call from someone at that company--- perhaps their engineer--- asking why are these windings reversed--- you (we) don't need to reverse these windings. And this just one example--- it's human nature in part--- the engineer knows what his companies production culture, technical, and craft capabilities and etc are--- he is going to take your design and in a great many (all in my particular experience) of the quotes just simply redesign the trans to fit their needs and capabilities. This especially being the case when your only asking them to build one, two or ten pieces of something. They just simply aren't going to change their way of doing things for a hundred dollar order.
So even under the best of circumstances--- even when you send the blueprint complete my experience was that getting someone to do it right was no simple task. Just imagine what's likely to happen where you (and you don't yourself have the knowledge to discriminate) send them a unit for a teardown---- who wants to bet on what level of "accuracy" as an outcome?
After a bit of the above experiences in the late eighties and trying to farm out this work-- I realized that if I wanted to do this (build tranneys) and do it right---- I was going to have to learn both the craft as well as the design (engineering) side of the business if I wanted to be a long term player and not simply someone who sold cheap knockoffs in a fly-by-night manner.
have I addressed your question at all ---- or did I go off the mark to far?
MSL