Amplifier for 144 MHz on a GU35B lamp. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / RF power amplifiers
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On fig. 1 shows a diagram of a powerful RA at 144 MHz, designed by the ultrashortwave UA1ZCL known among amateurs of EME communication.
The amplifier is made on a GU35B lamp according to the scheme with a common cathode. Capacitors C1...C9 block the heating and bias circuits of the first and second grids. C9 is constructive and is made in the form of a hoop covering the lamp. The excitation of the first grid is provided by the input coaxial resonator (from the PPC1M radio station), which is tuned by the capacitor C12, and coordinated with the PA input - C13.
To ensure stability, the neutralization of the lamp through-pass capacitance through the constructive capacitor C10, located in the anode compartment, was used.
Fig.1 (click to enlarge)
To reduce the coupling, C10 is separated from the anode by a PE screening partition, which is bent as shown in Fig. 1 and fixed to the case with two screws. A M10...M3 bolt is soldered to the C4 plate, which is brought into the inlet compartment through a PTFE gasket with an internal thread. By adjusting C10, stable operation of the cascade is achieved.
The output coaxial resonator consists of an outer tube with a diameter of 90...95 mm and an inner tube with a diameter of 32 mm and a length of 375...385 mm, which is connected to the anode of the lamp. An anode voltage of +3,5 kV was also supplied through the inner pipe through the corresponding chokes, bushing insulators and decoupling capacitors.
The output resonator is tuned by a constructive capacitor C15, which is a disk with a diameter of 80 ... 90 mm, to which an adjusting bolt is soldered, screwed into a nut soldered to the end of the resonator. To ensure reliable contact between the C15 disk and the end of the resonator, a curly spring made of thin brass or bronze is inserted.
The adjustment of the connection with the output is carried out by a constructive capacitor C14, made similarly to C10, C15.
For safety, the PA output is DC grounded through a choke.
Since the lamp consumes a significant amount of filament power, it is necessary to use a timer to delay the supply of grid and anode voltages. The scheme for generating the bias voltage of the first grid is shown in Fig.2.
Ris.2
Zener diodes VD1 ... VD8 are selected so that in the "RX" position, the bias voltage of the first grid would be regulated by switch S1 within 60 ... 120 V.
Author: UA1ZCL; Publication: N. Bolshakov, rf.atnn.ru
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