Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

How can I design and make a 1750khz IF transformer

  1. Jan 26, 2013 #1
    I am in need of some 1750khz intermediate transformers for an old tube project. I can find a few 455khz but not 1750khz. Removing turns from a 455khz IF transformer would raise the frequency but what would that do to the impedance?

    I thought I would be able to find quite a bit on the subject of rolling my own IF transformer either with a toroid or on a coil form but saw very little and find no 1750's listed for sale so I have to make my own.

    I saw one 3 year old thread that asked the question but the thread was locked and no answer had been offered. Can anyone help me?

    Thank you.
  2. jcsd
  3. Jan 26, 2013 #2


    User Avatar
    Science Advisor

    These IF transformers were never common, but, many years ago, you could just get an oscillator transformer from a AM band radio.
    These cover a range 455 kHz above the received frequency, so they already covered 1750 kHz. You just needed a suitable capacitor to resonate them.

    Now, all that is gone.

    You could make some tuned circuits and resonate them if you have a signal generator.

    You would make or buy some inductors then put a capacitor across each one and then ground one end of each tuned circuit. Then join the other ends with small value capacitors.

    As a guide, 470 pF would resonate with 18 μH at 1750 kHz.

    If you buy an inductor with an iron or ferrite core, the actual inductance will vary with frequency, so you would need to experiment with the capacitors.
    Last edited: Jan 26, 2013
  4. Jan 27, 2013 #3


    User Avatar

    Staff: Mentor

    What value capacitor does the 455kHz use in its IFTs? You might just be able to reduce it to get 1.75MHz.

    I think the old valve receivers typically used Litz wire for their IFT's. It would be difficult to make a good joint if you remove some of that winding. Maybe poorer quality receivers might have used single-strand windings on the IFT core? (Does it need to withstand much voltage? If not, maybe a transistor radio might have single-strand windings on IFTs you could salvage and modify.)

    I'm envious. What is your valve project?
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook