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What are IF Transformers?

What’s an IF transformer? So far, we’ve discussed how the radio signal is captured and filtered. How the oscillator works. How the antenna and oscillator signals are tuned. And how the converter tube mixes and amplifies. You’ve also learned that by adding the antenna and oscillator signals, we now have four signals at the plate of the converter. And that we only want to amplify the lower, intermediate frequency. The IF transformers filter away the unnecessary frequencies and help strengthen the IF signal. Here’s the first I.F. transformer from our antique radio. Inside, are a core, capacitors, and coils. Coils are windings of very fine wire. I.F. Transformers filter frequencies using the principle of resonance. As we’ve learned, when a signal runs through a capacitor and coil, the circuit tunes to the resonant frequency. I.F. transformers are tuned to resonate with the IF frequency of 456 kilohertz. The four frequencies from the converter tube are fed to the primary coil and the primary capacitor. The circuit resonates with the I.F. Frequency, and non-resonant frequencies are minimized. The IF signal on the primary coil creates a magnetic field that’s picked up by the secondary. So now the IF signal on the primary, is also on the secondary. As we’ve learned, the coils in a transformer are magnetically coupled, but electrically isolated. We also learned that the arrangement allows for transformation. Not that kind... Voltage transformation. Let’s review. Transformers change voltage by changing the number of windings in coils. If the secondary has the same number of windings as the primary, the voltage remains the same. If the secondary has fewer windings, voltage is reduced. And if the secondary has more windings, voltage is increased. This is usually the case with IF transformers to help boost the signal. Voltage transformation and isolation are important characteristics of all transformers, no matter how big, or small. Just as with the variable condenser, the IF transformer has variable trimmer capacitors. These are to fine-tune the primary and secondary, so the transformer resonates at exactly 456 kilohertz. Fine tuning is part of the alignment procedure which we’ll discuss in a later segment. IF Tube & Second IF Transformer After the first IF transformer, the IF signal is amplified by the IF tube, and further refined by the second IF transformer. Unlike the complicated converter tube that oscillates, mixes and amplifies, the IF tube just amplifies. So, instead of five grids, it has just three. The first grid is connected to the tube’s grid cap which gets its signal from the first IF transformer. As current passes from cathode to plate, the IF signal is amplified. Grid two is the screen, and grid three the suppressor. If you missed my segment on the converter tube segment, you may want to watch it to learn more about how a tube functions. The second IF transformer receives the amplified IF signal from the IF tube and refines it even further, just as the first IF transformer did. The result is a strong, highly tuned IF signal that’s ready for the detector tube. Be sure to join me for the next video where you’ll learn about the detector tube and amplitude modulation. To stay updated, please subscribe and click the bell. And if you like this video, give it a thumbs up. See you soon. #radiorepair #radio #electronicsrepair #restoration