What EXACTLY are you trying to build? - assuming it's a HiFi amp (rather than a guitar amp) then just buy a transformer - it's critical part if you want to get decent quality from it, just 'chucking windings' on a core is going to produce a crappy transformer.
If you are in North America, Hammond Manufacturing in Canada has a wide selection of both power and audio output transformers for vacuum tube use.
Check their website,
Guitar Replacement Hammond manufactures direct replacement transformers for popular tube amps from Fender, Marshall, Vox, Ampeg, Orange, Gibson, Silvertone and Yorkville / Traynor. General...
www.hammfg.com
They are reasonably priced, and since weight is significant, shipping won’t be free.
I was trying to learn now to design an build an audio output transformer. My EI core is too small for the transformer I wanted to build. It was just a learning project. Not going to learn anything this time.
If you are in North America, Hammond Manufacturing in Canada has a wide selection of both power and audio output transformers for vacuum tube use.
Check their website,
Guitar Replacement Hammond manufactures direct replacement transformers for popular tube amps from Fender, Marshall, Vox, Ampeg, Orange, Gibson, Silvertone and Yorkville / Traynor. General...
www.hammfg.com
They are reasonably priced, and since weight is significant, shipping won’t be free.