Re: 6-gang FM stereo tuner heads
The crystal RBW circuits in the HP 8566/8 are very similar to your third image, except a BJT is used in place of the phase inverting transformer. The compensation trimmer should help with filter symmetry, and I think that section is what needs tweaking in some places in my HP 8568B. The cal procedure is quite detailed and lengthy. I've got the gear here to do it all, but it might take me a long time...
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Regards, Jeremy G0HZU
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