SB-200 PROBLEM

Discussion in 'Amateur Radio Amplifiers' started by W7AFS, May 17, 2011.

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  1. W7AFS

    W7AFS Ham Member QRZ Page

    sb-200 recieve audio problem...with the amp off and in-line recieve audio is great.. as soon as i turn amp on recieve audio drops way down...amp tunes up and all is good in the respect...have noticed that moving the tune control on amp audio changes but still not even close to what it should be... HELP.....thanks and 73
     
  2. KM1H

    KM1H Ham Member QRZ Page

    Relay and the bias supply electrolytic caps would be the first areas to check. There should be a full -125-130V at the output of the bias supply in RX or TX.

    Carl
     
  3. W7AFS

    W7AFS Ham Member QRZ Page

    i checked voltage off the phono cable that hooks to the keying relay and i found that it is 135.8 volts neg.
     
  4. W8JI

    W8JI Ham Member QRZ Page

    You probably either have a short in the relay control wire, or you have plugged the SB200 directly into the radio and blown the radio amp keying circuit up.

    If the SB200 relay was bad it would cut out receive if the amp was on or off. A "bias" supply failure stops the relay from going into transmit, not receive.

    What would make the receive cut out when the amp power is on would be some ground or short on the "cold" side of the SB200 relay coil. Try unplugging the relay line at the SB200 and see if it clears the power on receive issues.
     
  5. W7AFS

    W7AFS Ham Member QRZ Page

    if i unplug the relay from amp it goes into recieve mode with great audio.....and no plate voltage as it should be.....the more i look into this the more i think i might have got a bad relay buffer
     
    Last edited: May 17, 2011
  6. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Unplugging the keying line shouldn't make the plate voltage go away.

    I think you mean plate current.

    Anyway, as Tom said, it's either a short in the cable or your keying circuit (in your transceiver) has let its smoke out due to trying to switch a high negative voltage it wasn't rated to switch.
     
  7. W7AFS

    W7AFS Ham Member QRZ Page

    the keying line from the transciever to the amp goes thru a relay buffer to protect the radio..it is new never used before this amp..
     
  8. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Then probably the relay buffer is shorted, or the cable between it and the amplifier is.

    Check it out with an Ohmmeter.
     
  9. W7AFS

    W7AFS Ham Member QRZ Page

    DUHHHHHHHHHHHH... i checked the cable and it is good but dummy me didnt think to check the buffer relay.. thanks for the jog...
     
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