Re: Improving Selectivity In Vintage Receivers
Had a better look at the first tuned circuit inside the HRO crystal filter box.
Two identical windings (looking very much like the ~2.2mH found in the grid tuned circuit for 1st IF).
The upper "pie" tuned by 2x 100pF to ground, the lower pie an untuned coupling winding from the mixer valve anode. The spacing of the windings is as close as practicable in this case.
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