[Roger Jones]

On Tuesday, 31 July 2012 17:30:47 UTC-4, John Byrns wrote:
The "rumble filter" circuit in this tuner is sort of interesting. Rather than

inserting a low pass filter in the audio section, it changes the time constant

of the AFC network.....

Typo... I think you mean "high pass".
Anyway, I've never heard of an audio-frequency-dependent AFC line (it would screw up oscillator frequency in the weirdest way, FM-modulating it at low audio), nor a rumble filter in an FM tuner - not needed.
Cheers,
Roger