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Cobra Cam 88

Discussion in 'CB and Export Equipment and Accessories' started by jammeejoe, Aug 11, 2005.

  1. jammeejoe

    jammeejoe Member

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    Does anyone know anything about these radios? I know they are older radios, but can they be made to talk. Can extra channels be put in them? Were they good radios? I like tube radios, but don't know anything about this particular one. Thanks, Ray


     

  2. nomadradio

    nomadradio Analog Retentive

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    To start, it's roughly 40 years old, more or less.

    If a dog ages seven years for every "human" year, I have to figure a radio ages at least 3 or 4 times as fast as we do.

    That would make it 120 to 160 'human' years old.

    The difference is that you can replace parts on a 1966 radio.

    How long that list will be is determined BOTH by the 'mileage' and the age.

    If it was stored wrapped in plastic, in a climate-controlled museum vault, it might still work. Or might not.

    The 'showroom new' radio will run for no more than a week or three at best, even if it performs out of the box. After that many hours of heat and stress, the elctrolytic capacitors will begin to "remember" how old they really are, and start to fail one by one.

    Every electrolytic capacitor will have to be replaced. They just don't last that long.

    Too bad it doesn't have an odometer like a car. Might make it easier to judge wear and tear issues.

    The relay will need its contact points cleaned. If it's worn from use, replacing it is a pain. JUST DON'T USE ANY KIND OF ABRASIVE ON IT. A strip of paper soaked in solvent, even just rubbing alcohol, will remove tarnish without removing precious metal plating on the contacts' surfaces. Fish the paper strip under the points, and draw it back out with modest finger pressure holding the gap closed, so the paper rubs against the contacts' surfaces.

    Tubes are a big question mark. A good tube tester is good for weeding out the ones that are REALLY no good. Tubes that check okay on a tester may still have funny noises, or 'crackle' noises coming from them in the radio. Our routine method is to 'tap' each tube with a fingertip, while running the receiver with a weak signal on it to check for this kind of defective tube. Likewise, the same "tap" test is applied to the transmit tubes, with the radio keyed, watching for noise on a 'scope screen. Even if the tester said a tube is okay, the radio is the final authority. If that tube misbehaves in the radio, it has to be replaced.

    Crystals will go bad from use. A quartz crystal is a moving part on the inside. After so many thousand hours, they just drift off frequency, and eventually fail.

    Sometimes they go bad from age alone. Used to be you could guess the radio owner's home channel by which crystals were farthest off frequency.

    But here's how the hit parade lines up, in order of likeliest-to-fail.

    1) ALL the electrolytic caps. This is a guarantee, not a guess.

    2) SOME of the tubes, maybe. The tester is your first, but not the only way to get a handle on how many are still good, and how many just aren't any more. If the sockets are dirty or tarnished, a "CONTACT" cleaner, the type that leaves NO residue may help the tube sockets. Just scrubbing the tubes' pins with generic ammonia-based window cleaner and plastic brush will tend to remove any gunk on the tubes themselves. Works particularly well for tobacco tar. Just rinse thouroughly and dry.

    3) Noisy controls. Every rotary control, including the channel selector, will no doubt be noisy or intermittent. A good-quality "CONTROL"-type cleaner with a lubricant (silicone is best) is what you need. A NON-RESIDUE "CONTACT" cleaner is not the same thing. If it removes the lubrication from sliding contacts in a volume control or channel selector, they wear out from the friction.

    4) The transmit-receive relay. Might be okay. Might not.

    5) Worn-out, drifted or dead quartz crystals. Pretty sure that radio has 14 of them in it.

    6) The built-in loudspeaker may be okay, but it's made from paper and cardboard. Even if it was stored in an unheated garage or attic for only a day, moisture will warp the speaker cone, and you'll need a new one. Or an external speaker.

    And if it was wrapped in plastic, with 5000 original miles, some control cleaner and ALL the electrolytic caps might be all you need. If it wasn't stored that well, the amount of crud you need to remove is a big influence.

    Or you could decide you want to restore a 1965 car. A modest, low-cost model like the Ford Mustang, say?

    You'll find that the balance of "age" and "mileage" issues will be longer, and pretty different. But the basic idea is very much the same. This radio is too old for a simple "repair" job to get it back on the air for day-to-day use. After 40 years, it's going to be a "restore" job, whatever the mileage.

    Oh, and just one more discouraging word. This radio has NO noise blanker, JUST and Automatic Noise Limiter (ANL) in it.

    If you are now using a base radio with a blanker, switch OFF the "NB" on this radio. If your local noise level is high enough, you will no longer hear weak stations that the blanker will "pull out" from the noise.

    If your local noise level isn't too bad, you'll hear okay on a working CAM-88. If the blanker made a big difference when you turned it off, that's a hint how many weak stations the CAM won't be able to hear.

    73
     
  3. Robb

    Robb Yup

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    Any alignment info for this one?
     
  4. sunbulls

    sunbulls Sr. Member

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    SAM'S # 9 I have that book, but it will take a few days for me to get around producing a scan.
     
    Shadetree Mechanic and Robb like this.
  5. sunbulls

    sunbulls Sr. Member

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    This is the schematic and service info. The receive IF is 475 Khz instead of the usual 455 Khz. Consequently this radio has some crystals that are more difficult to find among other parts radios. Hopefully these are within tolerance. The last page of the PDF includes the crystal matix configuration to help troubleshoot any far off frequency channels.

    Cobra CAM-88 Schematic.jpg
     

    Attached Files:

  6. Robb

    Robb Yup

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    Thanks, sunbulls!
    A local CB operator is going to bring one of these over today so I can take a look at it for him, so he needed that data so that I could go thru it for him.
    So, thank you again for this info!!!!
     
  7. sunbulls

    sunbulls Sr. Member

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    You’re welcome. I enjoy cleaning up and digitizing some of these manuals. With radios I’m restoring, I find it much easier for me to flip through pages on the big screen rather than fumbling through a book that’s taking up needed space.
     
  8. Shadetree Mechanic

    Shadetree Mechanic 808 On The North Side of Dover

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    That's a neat looking radio, now I want one. Haha!
     
    secret squirrel and Slowmover like this.
  9. Slowmover

    Slowmover Elmer

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    One is supposed to only “think” this . . . never to actually say it aloud.
     
  10. Slowmover

    Slowmover Elmer

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    That’s one great read!
    Thank you from the distant future.

    .
     
  11. Shockwave

    Shockwave Sr. Member

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    Skip this radio. The first time I saw one come up for sale, I had to buy it. Thinking it was a Cobra tube radio, it had to talk at least as good as the other competing names like Courier, Gemtronics or Sonar. What I learned was, if loud, clear audio was your goal, avoid any radio that has a 6AQ5 or 12AQ5 modulator tube, as opposed to the more common 6BQ5 tube. Simply put, smaller tube, equals less audio headroom available.
     
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  12. Robb

    Robb Yup

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    The can electrolytic 30-30-20uf cap gets hot pretty fast. The front panel has a switch on it close to the xtal board for a few hacked channels. The tx freq is off by about ~1.3k. A couple of the tubes seem to get hotter than some of the others, either leaky coupling caps or poor biasing - didn't check further.. The xfrmr is getting way too hot in rx just sitting there, the rectifier is OK but the can cap is suspect because there is a lot of hum in tx and rx. the other caps have been tested and are also in poor shape, they had been replaced some time ago. Didn't bother to align it, since the can cap is a $45 piece to replace it and keep it original looking . . .

    Thanks to all for the tech info and is much appreciated!
     
    Shadetree Mechanic likes this.
  13. Shockwave

    Shockwave Sr. Member

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    The first thing I would do is attempt to confirm the original channel crystals are close enough in tolerance to even work. If they are not, the radio is a parts set. Is the TX off by 1.3k on every channel or just 4 in a row or, every 4th channel? If we can identify the pattern, it makes it easier to try adjusting a cap value on the particular crystal in question.

    If you're satisfied with the frequency, then handle the can filter cap. I imagine you already know you can replace sections of the can by adding new ones underneath? Now those caps only cost a couple of dollars to replace individually. You can obviously keep the can on the chassis but you should disconnect the replaced sections, so when it dried out more over time, you do not run the risk of it placing a short on your B+.

    For the fussiest customers requiring the all original look on both sides, I've learned today's smaller electrolytics can actually fit inside the original can without too much trouble. I've seen videos (I think on YouTube), showing exactly how to "Restuff old can filter capacitors".

    Because this radio is a Cobra with tubes, I've kept it more than 20 years after restoring it. Although, it only got used one day before realizing even in new working condition, it lagged behind the others with the 6BQ5 modulator tube. When matched with the correct high impedance microphone, it does have decent audio. I was just hoping for more. The small cathode on the 12AQ5 tube just cannot support the emissions required, for "6BQ5 like" audio peaks.
     
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  14. sunbulls

    sunbulls Sr. Member

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    Cap replacement first! Preferably before a radio that old was turned on in the first place.
    This will help protect other components from damage and prevent a possible heart stopping shotgun blast you will never forget.

    I rarely replace those multi section can capacitors because of their price or availability. I usually disconnect the terminals and install individual caps underneath. I have also repacked those cans, but that process is reserved more for original esthetic reasons on a high end restoration. If you so desire, there’s lots of on-line info about repacking these cans with many different DIY variations. Caps are smaller these days, so packing them is not usually a issue.
     
    Shockwave and Shadetree Mechanic like this.

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