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Radio hacker and swing dancer Greg Charvat is at it again with his latest restoration, the Retro Boom Box. His local swing group was in need of a portable radio to use for impromptu Lindy Hopping, so he outfitted a 1940′s radio with modern batteries that they could use while on the run. Here’s what he has to say about it:

I hang out with swing dancers. We like to lindy bomb, where we dress up in vintage clothing and show up somewhere where there is no dancing with a boom box. We start playing an old song from the 30′s and start dancing. It can be kind of obnoxious but it is very festive. This has occurred in subway stations, at furniture stores, art festivals, and etc.

Our team was using a ‘boom box’ from the late 90′s, so i decided to upgrade to something more in the time-frame of our clothing. I found a 1946 battery powered (and AC) portable tube radio, the Olympic model 6-606. Unfortunately this radio is AM only and it requires type A filament and type B high-voltage plate batteries that are no longer available, and of course like all antique radios it needed restoration.

I restored the radio to original specifications. Then i hacked into it’s audio circuitry to create an ipod connection. There is a small toggle switch on the back so that you can select the audio source as either the AM radio or an ipod. From there i built a replacement battery pack to replace the type A and B batteries. This battery pack requires 16 batteries (costing over $30), 10 9V’s and 6 C batteries to power the radio for a reasonable amount of time.

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Comments

  1. Simon says:

    “It can be kind of obnoxious…”

    Good that you recognise that :) Sure, might be nice for a few minute novelty but could get old for bystanders really fast. Kind of like when you’re at a park or beach and a bunch of hoons show up with their noisy doof-doof cars.

    Nice project though. Was wondering how you isolated the audio input. Ipod into high voltage metal chassis would be bad! How do you know what kind of audio isolation transformer to use?

    1. Gregory Charvat says:

      A very good question Simon,

      You need to make sure that the audio isolation transformer that you choose can handle a 125 VAC voltage difference between the primary winding and the secondary winding. You are right when you say that when this radio is plugged into the wall (yes it can be either plugged into the wall or run off of batteries) then the chassis is hot.

      I think the safest thing to do if you were to hack this at home would be to buy a line-voltage isolation transformer, probably 40 watts or so. Isolate the line from the radio itself by powering the radio off of the isolation transformer, then use a computer power cord to ground the chassis and power the radio. From there you can tie your ipod into the grid of the first AF stage with a capacitor without the worry of dealing with a hot chassis. Or, run the radio strictly off of batteries and cut the line chord off the chassis forever.

      Instead of doing this i choose to use a smaller, lighter weight, audio isolation transformer that can handle the 125 VAC voltage difference between the primary and secondary coils. And i do use this radio both with batteries and while plugged into the wall. But it’s primary mission in life is to run on batteries so we can take vintage jazz music with the vintage sound anywhere, running off of line is just a bonus.

      Glad you liked it!! Send me photos if you try this hack.

      Greg

  2. Michael Black says:

    There’s no high voltage issue.

    The grid of a tube has little or no voltage on it, the stage feeding it is AC coupled. It makes sense to feed the iPod into the radio
    through a coupling capacitor.

    You’re likely thinking of an AC/DC radio, which has no transformer and thus the chassis can be “hot” in reference to ground. Those go out of their way to ensure the radio is isolated from the user, and yes, attaching something external to it can rsult in the ground being
    suddenly touchable by the user.

    But this radio is being run off batteries, so there’s no issue.
    The chassis/ground is at zero volts, and hence there is no
    issue about touching the ground and real ground, since at no point will the chassis be “hot”.

    Michael

    1. Gregory Charvat says:

      Hi Michael,

      Good point.

      I use this radio mostly with batteries, but yes, this chassis can be hot when you use it with AC. The design of this battery/AC radio is very unusual. It actually works with both batteries or AC. When it is in AC mode it is a hot chassis radio.

      There is a multi-pole switch in the back (in addition to my Ipod/AM radio switch) that will allow the radio to be powered from batteries or hot chassis AC. This switch is actuated when you shove the plug into the back of the chassis, where, one of the prongs on the plug actuates the switch.

      You can see this if you click here
      http://www.mit.edu/~gr20603/Dr.%20Gregory%20L.%20Charvat%20Projects/Olympic%206-606%20Photos.html
      scroll down then click on the photo labeled “old line cord must plug into this socket…”

      So to run the radio in AC mode just plug it in. To run it in battery mode you have to plug the cord into the back of the radio itself to change over to battery mode.

      Very interesting…..
      Greg

  3. Adam says:

    How long do the batteries last? Perhaps you could set it up to run off an outlet where there is one available. There are outlets in train stations and dance halls.

    Otherwise, a very cool hack!

    1. Gregory Charvat says:

      Very good question Adam. Because you asked i looked into the issue tonight.

      I measured 12 mA current draw off of the 10 9V batteries in series that make up the B+ 90V plate voltage supply. I am using Rayovac Alkaline 9V batteries, part number A1604. According to their data sheet
      http://www.rayovac.com/technical/pdfs/pg_battery.pdf
      this battery pack should last for 12 hours, where, the battery is drawn down to 7.8V and the battery pack is used for 2 hours every day.

      I measured 44.9 mA current draw off of the 6 size C batteries in series that make up the A+ 9V filament voltage supply. For this i am using Energizer size C batteries, part number E93. According to the data sheet:
      http://data.energizer.com/PDFs/E93.pdf
      this battery pack should last for approximately 150 hours with continuous use.

      So it looks like the limiting factor is the B+ battery pack made up of 9V batteries.

      And it looks like this radio will last for 12 hours.

      Greg

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