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Most TRF sets have a an antenna transformer and a coupling/tuning transformer between each TRF RF amp stage. Some sets leave the transformers out in the open turning each one 90 degrees to prevent coupling, some sets put the transformer tube and tuning cap of each stage in its own dedicated stage shield, others individually shield the can so it looks like an IF can.
Your set looks to be a single knob TRF those require a trimmer on each coupling transformer to adjust the set so each stage is peaked at the same freq and track properly with each other.
A transformer with one winding connected to a knob and one winding fixed is a variable coupling transformer...it's probably in the antenna circuit and probably acts as a RF attenuator (which was usually effectively the volume control in a TRF).
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