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KLB-300 Amplifier Overhaul (2x 2sc2879's)

Discussion in 'General CB Services Discussion' started by mrblue630, Nov 30, 2005.

  1. mrblue630

    mrblue630
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    G'day Folks....
    A few months ago i picked up a KLB-300 amp. The KLB amps were manufactured in Japan and were sold here in Australia back in the late 80's early 90's. Models include: KLB-110DX, KLB-240DX, KLB-300 and a CVS-450 UHF amp. These are models that i am aware of.
    This particular amp i purchased was in fairly good condition for it's age. Besides the meter being pushed in, everything else was in good working order.
    I fired the amp up into a 50 ohm dummyload and found that the input swr was high, and went up higher when i flicked the amp to Hi power setting.
    Output power was; 3watt D/K from radio, amp 50w swinging to 100w AM and to around 160w SSB, on a Bird 43 meter with a 250H slug @14v.



    Upon removing the cover i immediately found a few things that needed to be done to get this amp running to it's full potential.
    Here is a list of things that are needed or need re-doing.
    * The power lead; Lacking current capabilities and the cable itself was connected to the on/off switch. The on/off switch used in this amp is a standard miniture toggle switch rated at 2 amps. So thats approx 30amps of current going through a 2 amps switch...... :?
    * No Negative Feedback.
    * Hi/Lo switch affects input SWR....it's gotta go.
    * Hi/Lo input drive switch, Again affects input SWR...gotta go
    * No Regulator to control Bias Voltage.
    * Bias Voltage too low, need to replace bias resistor.
    * No Relay to switch Bias when TX & RX
    * Thermal Tracking diode. In this amp the diode is under the pc board touching the heatsink, this is ok but could be better.
    * All tunning caps, collector/emitter caps to be replaced with new Silver Mica Caps.
    * Input and Output Transformers (cores) to be rewound with new Teflon wire.


    [​IMG]
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    [​IMG]
    [​IMG]
    [​IMG]


    This is a schematic of the bias circuit used in this KLB300, mods included (Reg, Relay, Resistors etc....)
    Most of you could easily incorporate this bias circuit into their own 2 pill 2879 class C amp

    [​IMG]
     

  2. mrblue630

    mrblue630
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    Thanks Greg,
    I am currently moving house so i will post all the rest of the info on this amp when i settled.
    Just to let you all know though, i got this amp set up in the mobile at the moment and it's kicking ass!
     
  3. bob85

    bob85
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    nice job blue, where are the pictures? :LOL:
     
  4. Moleculo

    Moleculo
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    Webshots doesn't seem to like it if you link to their site, so I put the images in the Forum photo album.
     
  5. rfoverlord

    rfoverlord
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    tnx blue, for helping to further educate some of us so that we may enjoy our hobby a little more. 73
     
  6. Rb30

    Rb30
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    43WR30

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    Sorry to bring back an old thread but I have a klb-400 which has the same design as the klb-300 with 2x 2sc2879's. About 2 years ago I started modifying this amp with the diagrams and pics on this thread but family stuff came along and the project took the top shelf untill now. However I see that all the pics have gone from this thread and I looked on the home page for a photo album that Moleculo mentioned however I can not find it. Any help??

    WR30 (VK2DXN)
    vk2dxn@gmail.com
     
  7. mackmobile43

    mackmobile43
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    :sad: mrblue630 mrblue630 is offline
    Junior Member



    Last Activity: 02-13-2007 02:19 AM
     
  8. Rb30

    Rb30
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    43WR30

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    Ok I have found the pics on another site so all is good, oh and btw Mack thanks for stating the obvious there captain
     

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