[Amps] 120 Hz hum from Henry...

[Fuqua, Bill L]

I think there were a number of reasons for eliminating input chokes and going to capacitive input filters. 
1. AM may have played a part but there were others.
2. The use of solid state rectifiers eliminated the need to protect the mercury vapor rectifiers.
3. Cost savings is another. Besides the elemination of the input choke the use of centertapped transformers 
    ceased as well. That also reduced the amount  of iron and copper in the amplifiers reducing cost, weight and size.
4. Linear amplifiers were not usually used for AM. Most AM transmitters used plate modulators so they had lots of
     iron anyway and cost was not an issue. 

I personally prefer an input choke. It not only improves regulation but reduces the need for oversized house wiring to the 
to the amplifier. And reduces the capacitance required to achieve the ripple reduction and regulation of the power supply.
   The inductor's contribution to regulation is not the short term energy storage, that is reduced only to the limit of the 
high frequency cut off of the filter. A swinging choke really improves the regulation because the inductance get lower at higher currents and the power supply slides from a inductive input filter to one with a almost all capacitive filter stepping up the plate voltage a bit.  

Just some thoughts on the subject.

73
Bill wa4lav