## Saturday, February 13, 2016

### Let's build a transformer without high math

Need a transformer for that new set and either can't find it or find it priced out of reach? Not to worry. Wind your own. What would you need? A former such as this one.

 You can make your own from craft paper or cardboard but at 20 cents apiece why not purchase them with the core to match?
Yes you will need the core.
 You can make your own core also but not like these. With an Al of 3000 these are hard to beat.
I said no high math. Here's all the math you need.
 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.
Now for the math brace yourself.
 Yes all you need to know is the inductance you require and Al. Look at the description of the cores Al is 2890.
As an example say we need a transformer with 800 Ohm impedance at 150 Hz. Look at the chart and you will see we need 1.7 Henrys. now insert the values in the formulas and find the number of turns.

# 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.