Ancient radio repair

They sure don’t build them like that anymore. [J.W. Koebel] managed to take this 1934 Simplex Model P radio and bring it back to life.

So where do you start with a repair job like this one? Being a ham radio guy he has a good idea of what he’s doing, and started by replacing the AC capacitor with one which will provide quality noise filtering. He tried to make fixes throughout that would improve functionality and declutter the wire mess. This led him to find a snapped solder connection on the volume knob. Next he tested out the speaker and found that the primary transformer needed replacing. After as replacing the A67 converter (we’ve got no idea what that is) he swapped out the rest of the original capacitors, most of the resistors, and fixed the mechanical problems with the tuning dial. The result is a working radio that looks fantastic!

[via Reddit]

39 thoughts on “Ancient radio repair

    1. Eirinn, You are close my good sir. Everyone in the Amateur Radio hobby calls it “Ugly Style” and the entire metal case is used as a giant ground plane for the circuit.

  1. Hey, I’ve never had anything make it on Hack-a-Day before! I usually just read about other people doing awesome stuff.

    “Converter” is what they called the combined mixer+oscillator tube that could, in one step, shift the incoming radio frequency signals to the intermediate frequency which was easier to work with back then.

  2. From the Article: “(The 6A7 tube, affectionately called the converter, is the mixer+oscillator tube responsible for converting the incoming RF to the radio’s lower Intermediate Frequency or IF.)”

  3. This is very cool, these things aren’t junk like some people seem to think. They work, often forever, and they’re useful history. I hate seeing people trashing these.

    Cool job!

  4. Heh – just throw an RTLSDR in there, an Arduino, interface with the dials, and you should be good to go lol.

  5. I had a radio like this once, although it was a little more fancy with a nice frequency meter and whatnot. Anywho, the previous owner fried it (literally, nice little ball of fire). I tried to salvage it, but it was too far gone. Ultimately, I gutted it and replaced the innards with a two-way radio and hooked up the controls to the original controls and added a big old vox microphone on the side. Made a lovely prop for a zombie game I ran.

  6. Nice to see you featuring someone taking a radio like this and bringing it back to life – rather than the (seemingly more common) approach of gutting it and turning it into an ipod dock with added colour changing leds and an arduino.

    But then, I am in the process of restoring a 1950s electromechanical (strowger) telephone exchange – so I have an affinity for this sort of thing…

    1. As a guy who has strowger/step equipment, and frequents hackaday, I (counting…) I’ll sixth that. Are you a member of the TCI, Strowger, or c*net/VoIP mailing lists?

      1. @KL: I’m on the strowger yahoo group (and a few others) and I will end up on C*Net at some point – my asterisk box has a knackered mobo at the moment though.

        @Everyone else, I do have some bits and pieces on my blog, but I’m not all that good at getting around to writing things up so haven’t documented any progress made (or faults developed!) since Feb.

        Any posts about it turn up in this category though:

        http://www.paulseward.com/blog/category/phones/atm-50-7-restoration/

        Current state of play is that the linefinders developed a fault this week so it’s not working at all – and only one out of the 4 switches is fully working.

        One has a fault with the rotary hunting (it’s probably just the horizontal interruptors being out of adjustment) and the other two are missing their tie line circuitry so aren’t in use at all.

        Clear as mud right? ;)

  7. Important tip:

    If you have an old tube device, don’t just plug it in to test it. Damage can result. Capacitors and other devices are often damaged due to age and they can catch fire. Go read the excellent advice Out There on how to do this more safely.

    Putting a light bulb in series will limit the amount of current the device can draw. It’s a neat trick that doesn’t require much investment. You need a “real” bulb – an LED won’t work ;-)

    1. in the absence of a variac, a 100w bulb (or a series of 60′s or 40′s now that the 100w’s are unobtanium for some of us) will do nicely.

      1. Not sure of your location, but here in the US newly manufactured 100 W incandescent lamps are still available. Lamps that can replace the older less efficient lamps that can no longer be sold when the delayed legislation take effect.

    1. Rob , for some reason your site does not appear very well in my setup.To be precise the images don’t show.The moment they are loaded they get hidden and all that’s left are the borders(css,js?).

      +1 On the article request,none the less.That site seem like a treasure chest :D

    1. Nope! In the very late ’30s and post-WW2, they started experimenting with bakelite chassis boards which are widely regarded as total crap. Printed circuit boards didn’t start appearing until the late ’50s, but it wasn’t really until the ’60s they started really taking off. I’m working on a 1965 tube stereo hi-fi which is still point-to-point, even!

    2. Did they exist? Yes.
      But they weren’t common until well after WWII when factories were able to use mass production techniques developed during wartime for consumer products.

  8. A67 = 6A7 Osc/Converter tube. Basically the whole front end of the radio. Usually followed by a 6K7 (or two), then a 6Q7 for the detector and audio amp (duodiode/triode tube), then your choice of a 6F6, 41, 42, 6K6 or 6V6 on the audio output.

    1. PS: Some radios will have an extra 6K7 (or similar) before the 6A7, this is used as an RF amp. A 5Y3, 5Y4, 5U4, etc is used for the rectifier.

      Same basic arrangement for the cheap 5 tube tabletops.

      Octal: 35Z5 (rect), 12SA7 (osc/conv), 12SK7 (IF amp), 12SQ7 (det/avc/1st audio), 50L6 (output.

      Miniature (mid 50s-late 60s): 35W4 (rect), 12BE6 (osc/conv), 12BA6 (IF amp), 12AV6 (det/avc/1st audio), 50C5 (output, early variants of this used a 50B5, which has a different pinout, while electrically the same, it is not interchangeable with the 50C5.)

    2. i have:
      6A7
      ->glass 7 pin + top connection, no center key
      ->MARCONI RADIOTRON
      6K7
      ->metal 7 pin + top connection, /w center key
      ->GE (Electronic TUBE)
      6Q7
      ->metal 7 pin + top connection, /w center key
      ->Canadian Westinghouse Co.

      and a misc. 42
      ->Westinghouse RADIO TUBE
      ->
      that i assume is an audio final stage (output tube)
      … or just a very powerful RF transmitter tube.
      never found info on inet for that tube :(
      … works well for audio at ~2 or more watts of sound…
      so it IS a power output tube of some sort.

      1. and of course a BRAND NEW chinese counterfiet EL84 / 6BQ5
        that was manu. around year 2000.

        the 42 sounds WAY better.
        the EL84 / 6BQ5 is more powerful.

  9. I used to work in an electronics repair shop. I don’t know how many tube radios ( they were getting old by that time, though I’m no spring chicken myself) I repaired over the years (30+) that I worked there. Check the tubes, move on to the capacitors. Following the curcuit was actualy easyer in a tube set than a printed curcuit board.

  10. It’s kind of interesting to see how you young whippersnappers react to a simple P to P wiring layout. It used to be the only way to fly.

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