04 Tube Operation.pdf - Kambing UI

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for a tetrode or pentode is obtained through a dropping resistor and grid leak bias is used (see Figure 39A). In this system a high transconductance, low-µ triode is connected between screen and cathode, and the controlling bias for the small triode is taken from Figure 39A. Screen voltage control circuit for exciter keying or protection against loss of excitation when supplying screen from high voltage source. the tetrode or pentode bias developed in the grid leak resistor. When normal excitation is present on the r-f amplifier and grid bias is developed, the triode control tube is cut off and the screen voltage circuit operates normally. If excitation voltage is removed from the tetrode or pentode power amplifier, the bias voltage developed in the resistor drops to zero and the control triode becomes conducting. The current drawn by the triode control tube will increase the voltage drop across the series screen resistor and lower the screen voltage to a very low value. There is still some voltage on the tetrode or pentode screen and a small static anode current flows. Usually this remaining current is not enough for the anode dissipation rating to be exceeded. This value can be reduced further by the use of a second control triode in parallel with the first (this redundancy is also insurance against failure of the single triode), by putting a gas regulator tube in series with the lead to the screen before the screen r-f by-pass capacitor, or by introducing a small amount of fixed bias on the power amplifier between the grid resistor and the power tube grid. Figure 39B shows a method of keying a tetrode or pentode r-f power amplifier where the low voltage power supply for the screen of the power tube and for the anode and screen of the driver stage is keyed directly. This permits keying in a relatively low voltage, low current circuit. The key click filter capacitor, resistor, and choke are 64
simple and assure positive control of the keying waveshape. Figure 39B. A typical method of keying a tetrode or pentode amplifier. 3. 11 AMPLITUDE MODULATION A triode r-f amplifier can be anode; grid- or cathode-modulated. Anode modulation is the type most extensively used. A triode may also be operated under a linear set of conditions for amplifying an amplitude modulated driver. A tetrode or pentode r-f amplifier can be anode and screen, screen grid, control grid or cathode-modulated. Usually the system chosen is a combination of any of the previously listed Figure 40. Basic screen and anode modulation circuits. 65
Page 1 and 2: SECTION 3 ELECTRICAL DESIGN CONSIDE
Page 3 and 4: typically 66 percent, and stage gai
Page 5 and 6: Figure 25. Anode voltage and grid v
Page 7 and 8: on the technical data sheet for the
Page 9 and 10: actual value being determined by th
Page 11 and 12: D-C meter reading = 1/12 times (0.5
Page 13 and 14: that a tube that has been in servic
Page 15 and 16: maximum power input of 2.2 x 50,000
Page 17 and 18: 3.3 TYPICAL R-F AMPLIFIER CIRCUIT D
Page 19 and 20: Figure 30: Relative harmonic vs.res
Page 21 and 22: Figure 33A. Determination of Induct
Page 23 and 24: ferrite loaded impedance matching t
Page 25 and 26: It should be noted that the lead co
Page 27 and 28: variation vs. frequency in some VHF
Page 29 and 30: Another method of assuring that the
Page 31 and 32: all of the available cathode pins s
Page 33: Figure 38. Triode protection chart.
Page 37 and 38: screen modulation, the grid bias sh
Page 39 and 40: 3.13 STABILIZING THE AMPLIFIER 3.1
Page 41 and 42: Figure 41. Usual circuit supporting
Page 43: The procedure of checking for self-

04 Tube Operation.pdf - Kambing UI

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