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Thread: Three diode negative peak limiter

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    Three diode negative peak limiter

    Peak limiter for plate modulated rigs
    Background

    The three diode limter circuit below uses a keep-alive circuit instead of a tapped resistor, as in other negative peak limiter cicuits. This circuit provides a more constant load to the modulators and produces less distortion than other circuits.
    Circuit Details
    R1 = Plate Impedance of the RF Amplifier, power rating equals 1/20 of the modulator power.
    C1 = 20-40 uF. C1 is not needed if the keep-alive power supply has a similar cap on its output.
    Keep-alive power supply = 1/10 to 1/20 the B+ voltage, e.g. B+ = 1000 V, Keep-alive = 50 V. Current requirement is about 1/10 the current rating of the B+ supply.
    D1 and D3 voltage ratings should be at least four times the B+ Voltage for a good safety factor. D1 and D3 current ratings are about 1/10 the DC plate current of the RF final amplifier.
    D2 voltage ratings should be at least the B+ Voltage (preferably higher). D2 current rating should be three times the DC plate current of the RF final amplifier.
    Maximum negative modulation is controlled by the Keep-alive power supply voltage. The voltage level should be made variable with a variac or suitable sized rheostat.

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    rainmakersrepair (02-10-2016)

  3. #2
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    Like anyone on this forum is going to know what to do with this information. LOL.

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    awsome Doughboy !! you explained the Three diode negative peak limiter circuit very easy . thank you so much .

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    Quote Originally Posted by doughboy View Post
    Peak limiter for plate modulated rigs
    Background

    The three diode limter circuit below uses a keep-alive circuit instead of a tapped resistor, as in other negative peak limiter cicuits. This circuit provides a more constant load to the modulators and produces less distortion than other circuits.
    Circuit Details
    R1 = Plate Impedance of the RF Amplifier, power rating equals 1/20 of the modulator power.
    C1 = 20-40 uF. C1 is not needed if the keep-alive power supply has a similar cap on its output.
    Keep-alive power supply = 1/10 to 1/20 the B+ voltage, e.g. B+ = 1000 V, Keep-alive = 50 V. Current requirement is about 1/10 the current rating of the B+ supply.
    D1 and D3 voltage ratings should be at least four times the B+ Voltage for a good safety factor. D1 and D3 current ratings are about 1/10 the DC plate current of the RF final amplifier.
    D2 voltage ratings should be at least the B+ Voltage (preferably higher). D2 current rating should be three times the DC plate current of the RF final amplifier.
    Maximum negative modulation is controlled by the Keep-alive power supply voltage. The voltage level should be made variable with a variac or suitable sized rheostat.

    Name:  3diodeka.jpg
Views: 713
Size:  12.8 KB



    So are you using the circuit for a direct inject on like a cobra 29?

    Sent from my SCH-I605 using Tapatalk

  6. #5
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    This is for old tube rigs

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    ARCHBISHOP (02-17-2016)

  8. #6
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    Thanks Doughboy there are a few vintage plate modulated rigs out there still in service. Plate modulated rigs CB or ham is the best way to in my humble opinion unless you go Flex or Anan with a broadcast processor and a big linear

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    ������ dayyyuum ittt

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