|Main Page and Front and Side Views||Tank Coil Information|
|Interior and Back Views||Typical Operating Conditions|
|Circuit Description and Schematic Diagram||Power Supply Photos|
|813 Tube Information||Power Supply Circuit Description and Schematic Diagram|
The operating bias on the amplifier can be set to any value from 0 volts to the maximum available from the bias supply. However, experimentation has shown that operating the tube by setting the bias for a zero signal plate current of about 10mA produces the best results. 10mA keeps the zero signal input to the amplifier at about 25W and also provides a good bleeder load for the power supply. At an output of 200W, the regulation of the power supply from zero signal to 200W out is about 7.6%.
Maximum Power Output of 260 Watts:
Operating with the bias set for a zero signal plate current of 10mA, and driven by the Wingfoot VFO exciter, the 813 amplifier can produce an output of 260 watts on 40m as measured with a Bird wattmeter. This is consistent with the 813 data sheets.
Conservative Outputs of 250 Watts and 200 Watts:
Although the amplifier can produce 260 watts of output, the amplifier must be carefully tuned to achieve this maximum. Cutting the drive back to an output of 250 watts is a little easier on the amplifier, and keeps the plate dissipation well under the ICAS maximum of 125 watts. In most of my operating, I keep the output cut even further back to 200W, since this is the legal limit on 30m, where I often use the amplifier. This decrease of 1.1 dB from the maximum of 260 watts substantially reduces all operating currents and results in a cooler and thus happier amplifier.
Drive Requirements and Input Impedance:
With the 1:4 input transformer, the 813 amplifier can be driven with either tube or solid state transmitters. At 200W output the amplifier requires 16.5W of drive from the exciter on a frequency of 7.020 MHz. This represents a power gain of 10.8 dB. At 250W output the amplifier requires 26W of drive for a power gain of 9.8 dB.
Summary of Typical Operating Conditions:
The first table below summarizes the operation of the amplifier at an output of 250 watts on the 40m band. The second table summarizes the operation of the amplifier at a very conservative output of 200W. The third table indicates typical zero signal conditions.
|Test Frequency||7.018 MHz|
|Power Output||250 Watts|
|Drive Power||26 Watts|
|Power Gain||9.8 dB|
|Plate Current||160 mA|
|Grid Current||26 mA|
|Screen Current||7.5 mA|
|Plate Voltage||2241 Volts|
|Plate Input||359 Watts|
|Plate Dissipation||109 Watts|
|Test Frequency||7.020 MHz|
|Power Output||200 Watts|
|Drive Power||16.5 Watts|
|Power Gain||10.8 dB|
|Plate Current||130 mA|
|Grid Current||21 mA|
|Screen Current||6 mA|
|Plate Voltage||2290 Volts|
|Plate Input||298 Watts|
|Plate Dissipation||98 Watts|
|Zero Signal Plate Current||10 mA|
|Zero Signal Plate Voltage||2464 Volts|
|Zero Signal Plate Input||24.6 Watts|
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