you are right – the use of crystal radios with the sensitive piezo earpieces is important to notice. There were many funny constructions and “designs” for this kind of children’s tiny radio like this one:

    The content: a reception coil built as a variometer, one capacitor and one diode for detection. With a little more money you got a variable capacitor with a fixed coil for tuning (similar to the well-known Lectron tuning block). Reception of AM BC stations only with a cable to connect with the metalpart of a water pipe (as GROUND / EARTH, ~ antenna) or heating, and – of course – with the piezo earpiece.

    As an alternative to this piezo model you could use the good old headphone set (since ~ 1920) with one or two capsules, each 2000 Ω impedance. This type is a magnetic version, with coils on a permanent magnet iron, which moves a thin metallic membrane:

    A couple of years an exponential horn could be placed on a capsule to listen without this quite heavy metal headset:

    Much later a high-impedance Hi-Fi headset like the famous HD-414 (Sennheiser, ~ 1969) with 1800 Ω each channel (isn’t she lovely?) could be used with good sound quality:

    or the follow-up model HD-424:

    The sound with these models (open systems = you could hear what’s around you, e.g. telephone or housedoor bells) are really splendid, beleave me!



    • This reply was modified 4 years, 4 months ago by Guenther.
    • This reply was modified 4 years, 4 months ago by Guenther.