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Recapping older radios

Discussion in 'General CB Services Discussion' started by KALR 7570, Jan 28, 2013.

  1. KALR 7570

    KALR 7570
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    Hello all,

    I'm wonder if I should have my two thirty plus year old radios recapped. They both seem to be working okay. They're never been modded or "tuned up" in any way. I think this has a lot to do with why they've lasted so long.

    If I don't get them capped and there is a failure could the damage be more serious?



    Thanks for reading my post. Good conditions to you all.
     

  2. tecnicoloco

    tecnicoloco
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    Tweaknician in Training

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    To be on the safe side I will recap the radios,you could stumble to find replacement parts if the radios are over 30 years old,this depends on brand and model popularity

    My 2 pesos
    Tecnicoloco
     
  3. packrat

    packrat
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    A radio that age is just waiting to blow a cap, and possibly take out a power supply, etc. a lot depends on the value of the radio. If it is a cheap radio, often it is cheaper to let it be and replace it when it goes. How much of a gambler are you?

    PR
     
  4. Captain Kilowatt

    Captain Kilowatt
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    If it ain't broke don't fix it. A lot of people talk about, and some even suggest, recapping all the electrolytics in gear 20+ years old whether they need it or not. That suggestion is just plain stupid IMO. I have radios that are 30-40 years old and have never needed a single capacitor replaced and I have had radios 5 years old that did. In 35 years of being in radio with 22 years of commercial electronics servicing I have only seen one piece of gear irreparably damaged because of a capacitor going bad. It was an old rack mounted tube type piece of audio gear. A filament bypass ceramic disc cap failed shorted. It was not even an electrolytic. The power transformer overheated and went into meltdown filling the studio with putrid smoke.:blink: Lots of excitement for a couple minutes.:laugh:
     
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  5. Robb

    Robb
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    Yup

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    But if it is broke; then you must fix it.
    Right?

    When you replaced the caps in a non-working radio that is more than 25 years old, the caps were of dubious quality to begin with, then test all of the caps you took out and found 25% of them were bad; then you don't question why.

    I now have three more working +25 year old radios than I did after I recapped them.
    A SuperStar 360FM, 3900, and a Uniden/President Grant.

    There were bad caps, OK caps, and failing caps; that is all there was to it.
     
    #5 Robb, Jan 28, 2013
    Last edited: Jan 29, 2013
  6. Captain Kilowatt

    Captain Kilowatt
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    I just cannot imagine replacing ALL the caps in a radio that is 25 years or so old just because it is 25 years old. I mean, if you are talking about just the power supply filters and maybe the main audio output cap then OK fine but not ALL of them. 25 year old radios had dozens upon dozens of electrolytic caps in them of nearly every conceivable value from 1 µF to 100 µF.
     
  7. ExitThirteen

    ExitThirteen
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    Grumpy and Cranky

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    Normally, I wouldn't concern myself with replacing all the electrolytic caps in a radio, but I decided to do that on a President Madison recently. My President Madison is the MB8719 version, with the analog clock. It has the PC-411AD board in it.

    What a difference! It takes a lot to impress me, as I've been doing tech work for so long on these radios, but it really made a difference. The RX audio is brighter and louder, the TX audio is crisper, and the clarifier slides smoother.

    Out of curiosity, I checked all the caps I had pulled out of the radio. If I went by the 5% tolerance rule, 6 caps had fallen out of spec, with another 4 pushing spec. That's about 30% of the total amount of electrolytics that were in the radio.

    If a person really wants to make an effort to keep the radio extra nice, it certainly wouldn't hurt to replace the caps, if you have the time and the parts to do so. :)

    ~Cheers~
     
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  8. Robb

    Robb
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    Yup

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    The thing is, the caps that went bad in my radios - did so randomly. One had a bad cap in the PLL and the AM receive only. Another was in the receiver and the audio amp. And so on. Make what you want out of that; but that is what happened.

    EDIT:
    Do nothing if it is working. If it should fail and the reasons aren't apparent/obvious (like bad final or driver is obvious); then aging caps might be the problem. If you find one old bad cap; there may be more. When I was working on these radios and found a bad cap, I just went ahead and replaced them all. Once all of the old caps were out, I went through them all and tested them. Out of all three radios at least two caps were shorted outright in each. At least two to four more were so far out of tolerance that they were about to go bad in each. I have absolutely no idea why/how three different radios from three different parts of the country did this. Were the owners using too much voltage into these radios? Was it because they were all 25+ years old? Was it because Uniden used a cheap grade of cap? Can't say. Except that they all work perfect now.

    I'd rather just get over it by installing new caps (replacing the old caps) rather than have to deal with another (cap) problem somewhere down the line and have to open the radio up again.

    Do whatever you think is right . . .
     
    #8 Robb, Jan 28, 2013
    Last edited: Jan 29, 2013
  9. Captain Kilowatt

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    The bold part seems odd. When electrolytics go bad in an audio circuit the end result is lower levels overall but crisper sound as the lows disappear. I have no idea why the clarifier would respond any differently unless you cleaned the pot.
     
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  10. KALR 7570

    KALR 7570
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    Thanks for all the replies to my post. You've all made good points and given me a lot to think about.

    Normally I'm of the "if ain't broke don't fix it" mind set. But I also believe that an ounce of prevention is worth a pound of cure. I know these radios will probably need servicing sooner or later. So why not get it done now? But then again, why have work done that may not be needed? They appear to be working fine. However their performance could have degraded over time and I just haven't noticed because I'm used to them being that way. Such is my conundrum.

    Haven't made up my mind yet as to what to do. But I do have more information to work with. I thank you all for that.
     
  11. Klondike Mike

    Klondike Mike
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    I just recapped a Cobra 142 base unit. Wasn't having any problems for a 30 year old CB radio. But I wanted a radio that I could do rx/tx alignments too that would make it reliable for the next 30 years.

    I am now working on another classic CB radio, the Uniden Madison. It is having problems. I was able to get close to operational spec. but not quite on some parameters. I will be doing a total electrolytic cap replacement hoping that some of those "out of spec" parameters could be brought back in line and have another classic CB radio operational for the next 30 years.



     
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  12. 2RT307

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    When can we expect the video of it? I always enjoy watching your youtube stuff.

    73,
    RT307
     
  13. Klondike Mike

    Klondike Mike
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    I uploaded the final edition of the 142 last week;


    [​IMG]


    I'm uploading part 2 of the Uniden Madison now. It's 2Gb in size and will take a few hours before its available;



    [​IMG]


    Thanks for watching!
     
    #13 Klondike Mike, Jan 29, 2013
    Last edited: Jan 30, 2013
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  14. Captain Kilowatt

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    Considering the normal spec for standard aluminum electrolytics is +/- 20% for standard requirements and up to as much as -20% to +80% for capacitors that are used in a situation that simply requires a minimum value such as filter capacitors, replacing capacitors that are off by only 10% is a waste of time and money as there will NOT be a change in performance. Anyone claiming anything different is just fooling themselves. Something to consider before someone decides to replace everything just "because". Depending on the value, as much as a 50% reduction in value may not even be noticeable in the end unless there are several such capacitors in the same circuit.
     
  15. Klondike Mike

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    There are tech's out there that have actual experience working on these radio's for the last 30-40 years and don't necessarily know all the theoretical this or that.

    Sharing their experience with the community, there is a known history of failures and recommend replacements. As Edmund Burke stated, "Those who don't know history are destined to repeat it." I prefer to heed the warning.
     

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