Radio on the fritz ...

Discussion in 'Radio' started by tonyb, Dec 11, 2014.

  1. LizzieMaine

    LizzieMaine Bartender

    Well said. I think it's important for as many people as possible to preserve as many of the "old skills" as possible -- because otherwise they're going to wither away and die. We no longer have even one general-electronics repair shop in this area, so if someone owns tube-type electronics it's up to them to learn basic repairs and maintenance if they want to keep them operating.

    There are some excellent basic reference books that were used to train repair people in the past. One of my favorites is "Practical Radio Servicing" by William Markus and Alex Levy, published by McGraw Hill in 1963. This is a vocational-school textbook that was a real help to me when I was starting out, and it's still a useful reference. It gives you just enough theory to understand what's going on and just enough basic technique to fix it. Markus's "Television and Radio Repairing," from 1959, is also good, albeit more advanced. It might be worth tracking down these volumes and giving them an examination if you find you enjoy radio work.

    If I had to give one piece of advice it would be this: once you've got your radio operating again, consider replacing *all* of the wax-covered paper condensers under the chassis. Because they're simply rolled-up foil layers with a layer of thin paper between them, they're prone to failure as the paper deteriorates, and when they go, they can cause a lot of damage. Replacing them with mylar-foil unitsl is tedious -- but once it's done, you can run your radio all day long every day of the week without worrying about it going up in smoke.
     
    Last edited: Dec 13, 2014
  2. tonyb

    tonyb Vendor

    Messages:
    7,375
    Location:
    My mother's basement
    Okay, got a multimeter at HFT. Fifteen dollar unit marked down to $4.49, plus another 25 percent off because I'm charming or good-looking or something. Out the door for $3.62 with the tax.
     
  3. LizzieMaine

    LizzieMaine Bartender

    Very good. Let me know what readings you get on the transformer.
     
  4. tonyb

    tonyb Vendor

    Messages:
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    Location:
    My mother's basement
    Okay, now that more urgent matters are tended to, I can take a look at this thing.

    Real basic question No. 1: To perform these initial diagnostics I have to remove the chassis from the cabinet, right? Problem is that the speaker is mounted independently of the chassis, so that I would either have to remove it at the same time or perhaps disconnect the wires running to the speaker, so as to be able to move the chassis around any old way I wish.
     
  5. Stanley Doble

    Stanley Doble Call Me a Cab

    Messages:
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    Location:
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    If you look closely, the speaker is usually connected to the chassis with a plug. You can simply unplug, and plug it back in when you are finished. This is not always obvious if the plug is made of metal.

    This is too obvious but do not do any work unless the radio is unplugged. There are parts in there that operate at up to 400 volts and can give you quite a lifter.

    Capacitors or condensers, can hold a charge long after the radio is unplugged so be careful around them too.
     
  6. tonyb

    tonyb Vendor

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    Location:
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    Oh, believe me, I know through bitter experience that it's best to proceed on the assumption I know nothing, because sometimes what little I do know turns out to be more dangerous than knowing nothing at all.
     
  7. Stanley Doble

    Stanley Doble Call Me a Cab

    Messages:
    2,772
    Location:
    Cobourg
    I have a little gadget in my toolbox made of 2 alligator clips soldered to a 10000 ohm ceramic resistor. I use it to safely discharge capacitors. Any time I am in doubt I connect it for a minute, or just short it out with a screwdriver. The screwdriver makes a spark if the cap is charged but I figure that is better than me getting a lifter.
     
  8. 1930artdeco

    1930artdeco Practically Family

    Messages:
    548
    Location:
    oakland
    I like this thread as I have two antique radios that I cannot fix-but a friend can. I just have to drive three hours to his house. So I am liking how LizzieMaine is describing things. So I will be watching it to learn a thing or two or three. I may even look for those books.

    Mike
     
  9. tonyb

    tonyb Vendor

    Messages:
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    Location:
    My mother's basement
    I'm in no hurry to fix this thing. It certainly isn't that its being out of service leaves me without a radio to listen to. And I'd rather take my sweet time than damage it in my haste and ignorance.

    So, a real, real, basic question ...

    I gotta get the chassis out, but the outside control knobs gotta come off first, right? How to do that without damaging them? I see nothing like a set screw on the knobs. I pull one knob forward, as one did to remove the knobs on lotsa 1960s-vintage car radios, but that doesn't remove the knob but rather pulls the whole works forward.
     
    Last edited: Jan 2, 2015
  10. LizzieMaine

    LizzieMaine Bartender

    There might be a very small set screw you're not seeing set into the edge of the knob -- check that first. If not, try a little dab of penetrating oil onto the shafts behind the knobs and let it trickle into the fitting. Sometimes knobs will freeze onto the shafts, especially if there's a brass insert in the knob to hold it into place. Don't try to force it with a screwdriver if the knobs are plastic -- they could easily break. Slow and patient wins the day.
     
  11. plain old dave

    plain old dave A-List Customer

    Messages:
    472
    Location:
    East TN
    Something that has not been mentioned on this thread is one thing I have seen old timers use to fire up vintage HF gear and minimize the risk of catastrophic electrolytic capacitor failure:

    A variac.

    This is a gadget that you plug an electric radio into that GRADUALLY increases the applied voltage to @110VAC.

    Lizzie makes a good point that the "radio shop" is more or less a thing of the past, but a lot of Amateur Radio clubs will have older operators that date far enough back to actually have earned their ticket when tubes were the only way to go. And a lot of the older guys still have the gear to work on electric (tube) radio gear; I knew 2 OMs that got their licenses right around WW2. And one of them STILL HAD his pre-WW2 equipment for the old 2 1/2 and 5 meter VHF Amateur bands and operated CW (Morse Code) with a WW2 surplus Army Air Corps leg key, in his car. THOSE are the people you need to find locally.
     

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