I recently came across an old radio that has these odd parts on them. They are labeled "T3" and so on, so maybe they're some kind of capacitor or transformer?
They're adjustable at the top and branded/stamped "JET" around the adjustment screw.
In the last picture, I carefully dissected one and it's just thin copper wire wrapped around what seems to be a ferrite/iron core.
Any ideas?
They're IF transformers (T is for Transformer) used in radios (relatively narrowband amplifiers at the Intermediate Frequency of usually 10.7MHz for FM and 455kHz for AM).
The ferrite core adjustment is for trimming the inductance to tune the center frequency, called "aligning" the radio. Below image from this datasheet.
There are many variations and you need some equipment to properly align a radio, which does not bode well for your chances at success.
These are variable inductors used for trimming specific frequencies. Usually, you also need an oscilloscope for repairing and re-aligning these old receivers. Here's a YouTube channel that specialises in doing exactly that: MrCarlsonsLab
Alternatively, you could measure every component in the circuit with a precise multimeter and figure out what value you're supposed to set these at by understanding what particular frequency the component arrangements are filtering out. Here are some online calculators for simple frequency filters:
They are well known Intermediate Frequency Transformers (IFTs) and not rare. The transformer primary and secondary windings would be on a ferrite bobbin surrounded by a threaded 'cup' core. There would also be a ceramic capacitor across the primary winding. The winding ends and the capacitor leads would be soldered to the pin terminals of the IFT, enclosed in a brass or aluminium housing. By adjusting the cup core the primary winding/capacitor would be made to resonate at the required intermediate frequency. The frequency would generally be 455 kHz for AM and 10.7 MHz for FM.
Yes, intermediate frequency transformers used in a superheterodyne receiver. Commonly 455kHz for hf receivers. They cans be set slightly staggered to adjust the bandwidth of the if amplifier. Also 10.7 MHz transformers for FM receivers. The oscillator in the superhet receiver will also use one. The oscillator tracks the input tuner the two frequencies are feed into the mixer and four frequencies can be detected from the mixer. The signal frequency, the oscillator frequency and two heterodyne frequencies one unwanted and one wanted. A double superheterodyne receiver is preferred for the higher frequencies. Crystal filters may be used in the amplifier to give certain bandwidths. The last IF will have an output winding to match into the demodulator.
These are IFT coils used in radio as well as in b/w tv for converting single high to low & low to high for better response.
Intermediate frequency 455KHz transformer
