|You can make your own from craft paper or cardboard but at 20 cents apiece why not purchase them with the core to match?|
|You can make your own core also but not like these. With an Al of 3000 these are hard to beat.|
|It would be hard to wind a transformer without knowing the value of inductance you need. So look at the chart and select a value.|
|Yes all you need to know is the inductance you require and Al. Look at the description of the cores Al is 2890.|
# of turns = Sqrt (1700/2890)*1000
# of turns = 767
The secondary would be the sqrt of the turns ratio. suppose the load is an 8 ohm speaker then 800/8=100 and the sqrt of 100 = 10 so we need about 77 turns for the secondary. I would allow a little for losses and go with 800 turns primary and 80 turns secondary.
The size of wire would be determined by the current required. Basically the smallest wire you have will work for the primary and go up a size or two for the secondary unless you're building a power transformer or surround sound system.
The above core and formers are available at Surplus Sales of Nebraska for about $1.50 per set.
I don't sell them I'm just a satisfied customer.
I made the former and used banding material on these transformers:
Using banding straps as the core
They are not as neat as the manufactured one but they work.