Checking the 50 Hz hum of alternating current in a loudspeaker, a crude 'oscilloscope'!

 I connected a step down transformer to the input of an amplispeaker with a 50K cermet preset potentiometer to listen to the 50 Hz hum of alternating current. The intensity of hum increased gradually when the resistance value of the preset was reduced to half gradually. Of course, I did not attempt reducing it fully for fear of blowing out the input circuit of the amplifier with over 10 V in the output of the step down transformer. I used the same method to check for any hum in the filtered output of the bridge rectifier which I made the other day. I could not hear only a minimal hum. It was a crude method of checking the output waveform short of an oscilloscope!



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