Project Zenith

21st century spin on a early 20th century product.

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Scored this vintage retro radio free on the side of the road. Rather than try to make it's tired old tube system work, I plan to modernize it and refit it to be awesome. It'll still look stock on the outside, and will even work much the same as it originally did, but now it will also have bluetooth connectivity, fancy lights, be internet connected, etc.

My near 2 minute long video describing the plans for the project.

  • 1 × 6amp bridge rectifier Converts 120v AC to 120v DC, roughly
  • 1 × 330uf 450v capacitor Smooths out the recified DC. Due to the charge pump effect with the diodes, it also steps the voltage up to about 160v DC.
  • 1 × Motorola "Moto Stream" Bluetooth audio adapter, allows up to 5 devices to pair with the radio.

  • Powering up the speaker

    UnaClocker07/08/2014 at 01:09 0 comments

    This is the original, 74 year old speaker in this unit. While I probably won't use this for the primary audio output, I do want to have it functional. Zenith was really thinking outside the box when they designed this unit. One of their unique ideas was to not use a permanent magnet on the speaker. Instead, they used an electromagnet. From what I've read online, the original tube system used the coil on this electromagnet as the "choke" in it's power supply system. Me, I just need to power that magnet up so the speaker works at all. I checked the resistance of this coil with a multimeter, and it shows just over 1k ohms. Some quick ohm's law on that, and I see that it'll draw about 14watts at 110 volts. So I don't need to use a transformer to step line voltage (what comes out of the wall) down, I can simply feed it straight into the speaker, after rectifying it (converting it from AC to DC). It has to be DC because you can't run an electromagnet off of AC.

    That's a 25cent 6 amp bridge rectifier. Nice simple converts AC to DC, up to 700 watts.

    I found that if I simply run the speaker off the rectifier, I get a pretty strong hum noise even with no signal running to the speaker. So I grabbed this old capacitor out of a dead plasma TV.

    Due to the charge pump effect with the alternating voltage and the diodes in the rectifier, the voltage went up to 166v with the capacitor in the circuit. A bit higher than I had really wanted, but it still works.

    I end up with a 25watt draw at the wall, just powering the speaker's electromagnet. I'll definitely need to put this on a solid state relay so the speaker is only powered up when I'm actively using it. If I find a transformer that can step me down from 120v to about 80, I'll use that in the future, for now this will work. The coil does not seem to generate any heat in my short tests (3-5 minutes).

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Adam Fabio wrote 07/28/2014 at 03:27 point
Great project! I love that you're keeping the old parts (like that electrostatic loudspeaker speaker) functional, yet bringing new parts in to this old radio. Thanks for entering the Hackaday Prize! Your two minute video looks great - but keep the updates coming in!

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kc8rwr wrote 07/25/2014 at 16:16 point
Actually the electromagent in that speaker wasn't so "outside the box". Permanent magnets weren't as good back then so most speakers worked that way. Consequently for people trying to restore old radios the speaker can be a challenge. Speakers with field coils (that's what that electromagnet was called) are hard to come by. So, the restorer has to chose between hunting down a rare and possibly expensive speaker or replacing the field coil with a choke since it is part of the power supply. Since you aren't trying to restore it you might want to consider selling the speaker and replacing it with a modern one. You just might be able to fund part of your project with the difference plus you will make some restorer very happy!

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jlbrian7 wrote 07/07/2014 at 12:42 point
If you think that any of this would be useful feel free to use it One of these days I plan on getting a full console radio for the house myself.

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