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Oddball transitors.

Discussion in 'Amplifiers' started by Staybolt, Jun 8, 2018.

  1. Staybolt

    Staybolt Well-Known Member

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    Hello all. I have a little 2 pill amp that I think is dead as it don't pass RF. It uses some transistors i've never heard of. They are Motorola SRF 866K.... Is there a crossover for these as I cant find them anywhere online.. They are stud mount...


     

  2. Onelasttime

    Onelasttime Well-Known Member

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    What package is the transistor? Stud mount? What is the name, make, model of the amp etc??? If it is not a stud mount and is a common board used in many other re-branded CB amps then you will likely find that many common transistors like the MRF455, MRF454, 2SD1446, Toshiba 2SC2879 can be made to work but that is just a guess at this point. Feed us more data! LOL
     
  3. Staybolt

    Staybolt Well-Known Member

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    I mentioned stud mount in my post.
     
  4. Staybolt

    Staybolt Well-Known Member

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    Motorola srf 866k is all i know. Thats what it says on the top. Its in a weird little amp that has no on off, ssb am, or preamp switch. You hook it to dc and hook the radio and antenna to it and its always on... says Wren House Electronics on it...
     
  5. midnight special

    midnight special Well-Known Member

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    pictures please
     
  6. Staybolt

    Staybolt Well-Known Member

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    Pic 1
     

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  7. Staybolt

    Staybolt Well-Known Member

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    Pic 2
     

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  8. Staybolt

    Staybolt Well-Known Member

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    Pic 3
     

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  9. Onelasttime

    Onelasttime Well-Known Member

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    I can only imagine they used a high current circuit breaker or switch to remotely turn it on and off. I have never seen that board though or that style of cores on the transformer. Do you have caliper or micrometer that is accurate handy to physically measure the dimensions of the transistors?
     
  10. Tallman

    Tallman W9WDX Amateur Radio Member, KW4YJ EXTRA class

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    I have a base amp that uses the stud mount transistors. I played hell finding those parts but I did find some on eBay for a reasonable price. I have not installed these yet because of other more pressing issues. When you find your replacements Do Not over tighten the stud mounts. Be very judicious with the heat sink grease under these types of transistors. Too much grease will hamper the heat transfer and be sure to note the stacking of the mounting hardware.
     
  11. Staybolt

    Staybolt Well-Known Member

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    You got me lost there guy!!
     
  12. Grinder74

    Grinder74 KE8EOJ

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    Diameter of pill. Overall length to tabs end to end.
     
  13. nomadradio

    nomadradio Analog Retentive

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    The prefix "SRF" indicated transistors that were special-ordered from Motorola. Generally a part found in their catalog, but selected for a particular final-test result. Not sure how many you had to order to get the house-number marked on it, but there was most certainly a minimum order quantity for that.

    Good chance that it's a house-marked type MRF455A. The "A" suffix letter indicates the stud-mount package. The MRF455 without the A is the flange mount with two screw holes for mounting.

    This transistor is incredibly easy to overdrive, and usually calls for adding some resistors between the relay and the primary of the input transformer.

    73
     
    rabbiporkchop likes this.
  14. Onelasttime

    Onelasttime Well-Known Member

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    Well he said it does not have any externals switches and no remote so if you wired it to a battery directly it would be on constantly draining your battery in no time. So you would still want a way to turn it on and off.

    In early car audio, you ran into this as well. High current switches rated for continuous duty used to be fairly common before solid state took hold of the world.
     
  15. Onelasttime

    Onelasttime Well-Known Member

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    One of the things I always liked about Motorola rf bjt's is how little drive they need for full output.
     

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