The PHILCO Phorum
output transformers - Printable Version

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output transformers - loneddie - 05-18-2020

I need to know how to determine what size wire to use to create an output transformer to match a 3Q5 tube.  Tube is 8K ohms plate resistance.  Speaker is 3.2 ohms.  Transformer is 440 ohms resistance.  Speaker is 3.2 ohms.  Also, how many feet of wire is needed?  Cannot, thus far, locate this info on line.  Help? Icon_sad   William Hardy. loneddie@cfl.rr.com.

RE: output transformers - Radioroslyn - 05-18-2020

You'll have to open the winding up and measure the diameter of the primary wire. Best guess it's going to be pretty small like 40-50ga. Once you know the size you can determine the length.

RE: output transformers - morzh - 05-18-2020

Or....if wanted, unwind the wire and count the turns.
Also....you are bent on rewinding, or could you aford to buy a universal Hammond?

RE: output transformers - loneddie - 05-18-2020

can't count windings.  radio did not have an output transformer.  yes, I can afford to buy a Hammond.  however, I am stubborn and desire to learn how to create and wire such.  last hope, where do I buy the Hammond? Icon_biggrin

RE: output transformers - loneddie - 05-18-2020

that's my problem.  I don't know how to calculate the length of the wire.  At least, I think I know but need to rely on better guidance than my old noggin Icon_eek

RE: output transformers - Brad Winder - 05-23-2020

     Here is a chart, from the Radio Troubleshooters Handbook:

RE: output transformers - morzh - 05-23-2020

Eddie

You need to know number of turns. And the gage.
And then what it takes, it takes, just have a spool big enough.

You DON'T go by resistance. You go by turns ratio.
And thatis dictated by the impedances, you turn ratio is square root of your impedances ratio.

Now, the number of turns of the primary is calculated either by formulae, or from tables that are in existance, given your minimum needed DC resistance and inductance, that determines your frequency response.

You probably could find a typical transformer design for your tyoe of output tube and the load.