Amp Voltage

Discussion in 'Amateur Radio Amplifiers' started by W8NIC, Nov 9, 2019.

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  1. W8NIC

    W8NIC Ham Member QRZ Page

    Hello gang!

    I have a Drake L7 and 2 power supplies. One shows 2700 plate volts, when driven with 65 watts, amp puts out 800 watts. The other one will do 3700 plate volts and will do 800 watts with 35 watts drive. Will the latter harm the amp in any way? Is 1750 watts at the plate too much for the two 3-500z tubes?

    Thank in advance.
  2. W1QJ

    W1QJ Ham Member QRZ Page

    Are both power supplies Drake? Normal voltage is around 2600 nominal. A 3-500 can handle 3700 volts no problem. Henry tan them as high has 4000 volts. The problem is the RF deck handling the voltage and not so much the tube.
    KU3X likes this.
  3. N8FVJ

    N8FVJ Ham Member QRZ Page

    I believe the 2700 volts is normal for the Drake L7 amp. The 3-500Z tubes will take up to 4000 volts, but the Drake PI network in the amplifier is designed for the lower voltage. I would use the 2700 volts. The 3-500Z pair of tubes can take about 2500 watts input at 60% amplifier efficiency.
    KU3X likes this.
  4. N8FVJ

    N8FVJ Ham Member QRZ Page

    Drake L7 uses 2500 volts from the factory power supply. 2700 volts is perfectly acceptable.
  5. W8NIC

    W8NIC Ham Member QRZ Page

    once again, thanks to the amp gurus!!
  6. W8NIC

    W8NIC Ham Member QRZ Page

    The 2700 volt is a Drake and the 3700 volt is homebrew.
  7. AI3V

    AI3V Ham Member QRZ Page

    With 1750 watts dc input ("watts at the plate")

    And 800 watts rf output

    Thst gives 950 watts of heat dissapated in the 2 tubes.

    The "500" in a 3-500z tube is the amout of heat it can dissapate (assuming adiquate cooling)

    Since 950 is less than 1000 you should be ok.

  8. W8NIC

    W8NIC Ham Member QRZ Page

    Thank you. That’s really information. Goes to show I don’t know much about amplifiers
  9. N8FVJ

    N8FVJ Ham Member QRZ Page

    1750 watts input with 60% efficiency is 1050 watts. Every tube amp is at least 60% efficient.

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