In building HV transformers for demonstration pieces, I've noticed that the biggest problem is locating suitable core material, which needs to be a rod or bundle of small rods. The old books usually specify a bundle of "soft iron wire", which is virtually gone from the marketplace. Soft steel is not too hard to come by, but it has just a bit too much residual magnetism to really work well. There are some excellent transformer core materials out there, but the companies who sell it only want to deal with large maunufacturers and don't sell to individuals. SO.... where can one get good transformer materials? OR what are good alternative materials? I'm wondering if a large ferrite rod would work in this application? Any other ideas?