@stan2004 posted:Tried searching but could not find a description of how the sound worked. From what I could gather, the phonograph signal is mixed with 60 Hz (or DC) track voltage. And from what I can see the tender had not much more than a speaker in terms of electrical components. So given the technology of the period, I'm thinking the tender speaker is simply playing the 60 Hz track voltage along with the higher frequency audio from the phonograph. And the speaker did not have sufficient low-frequency response to the 60 Hz "hum."
American Flyer superimposed the horn or whistle sound waveform on the track voltage and passed it to a loudspeaker on the train through a crude high-pass filter that rejected the 60-hertz power-line frequency.
I'm thinking this used the same and it looks like they mention this in this picture "Condensor Pack"
Further, they then had the user connect a different condensor across block sections of track to carry the audio signal.
