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need some info on a president dwight d cb

Discussion in 'Amateur Radio Modifications' started by lost bandit, Mar 7, 2018.

  1. lost bandit

    lost bandit Member

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    i bought a nice dwight d and after taking voltage off the switch i notice it had 15.3 volts i was pluged in to ac power if this voltage is high is there anyway to lower it .....also would like to lower the watts down to around 1 watt but was told this could not be done on this type of radio. its a am radio and has the d2816c pll chip if that helps any.thanks


     

  2. dozerman

    dozerman hello, its me again

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    doesnt it have a variable trimmer on the power supply board to raise or lower voltage? mine has. if it doesnt i would think the voltage regulators are failing on that board. mine had the same problem. as far as dead key, i used the diode beside the modulation transformer. took it out and added diodes in series until i had the desired key. mine keyed about 5 and swing to 15 or so. i think it took 4 total diodes to get it to 2 watts key. wont get a whole lot out of that 2096 final. im assuming this is still accurate, mine has the 878pll i think.
     
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  3. nomadradio

    nomadradio Analog Retentive

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    Just to the front of the power transformer is a small circuit board. Has only one trimmer pot on it. This is the power-supply voltage adjustment. Wattmeter worshippers will crank it for all they can get. If the trimmer pot won't change the voltage, then there is an additional problem.

    There is a 4.7 ohm resistor in line with the driver transistor, similar to the jumper wire that you remove from a Cobra 29LTD to install a carrier control. R49 is behind the heat sink just behind the driver transistor.

    The typical TIP120 variable setup will go in place of R49, or you can substitute a higher-value resistor with an electrolytic capacitor in parallel with the resistor. The capacitor serves to allow the modulation audio to reach the driver transistor as if the carrier were turned up to the normal level. Without the capacitor, the carrier and modulated swing will both be reduced. The resistance value needed for the desired carrier level is not a precise thing. A 47-ohm half-Watt or larger resistor will typically reduce the carrier down to couple of Watts more or less. A 100-ohm resistor is around the typical upper limit where the carrier falls below half of a Watt. This is a cut-and-try process. The power-supply voltage setting affects this, too.

    The circuit is about the same thing as a Cobra 29LTD, but the layout of the parts is totally different.

    73
     
  4. lost bandit

    lost bandit Member

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    thanks it has the 1969 final almost the same board as the 29 .i will check that trimmer out.
     
  5. lost bandit

    lost bandit Member

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    thanks for all the info. all of the replies has been very helpful.thanks
     

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