Broadband power amplifier. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / RF power amplifiers
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Many radio amateurs have transceivers with an output power of less than 5 watts. Such power is clearly not enough to operate on the air and excite tube amplifiers according to the grounded grid scheme. Therefore, the need for silos is obvious.
The scheme of the proposed amplifier (Fig. 1) does not differ from those already described in the literature. Its peculiarity lies in the fact that as the cores of high-frequency transformers, not scarce rings of 200 ... 400 HN are used, but cores from line transformers of television receivers. Despite the fact that these ferrites have a high permeability, the drop in frequency response at 30 MHz does not exceed 3...4 dB.
Due to the fact that such schemes have already been described in the literature, we will focus only on the design features of the silo. Coils L1, L2 are wound on a ferrite rod with a diameter of 8 mm and a length of 10 mm and contain 80 turns of PEL 0,1 wire.
The cores of transformers T1, T2, T3 should be wrapped with PVC electrical tape before winding. Their design is clear from Fig.2. Transformers are wound with a twist (1-2 twists per centimeter), with PEV 0,5 wire. After winding, the transformer is also wrapped with PVC tape. The manufactured transformer is enclosed in a screen (Fig. 3), made of foil fiberglass and soldered to the board. At the output of the amplifier, it is necessary to install a low-pass filter, described in the "Handbook of a shortwave radio amateur" Bunin, Yaylenko, 1984, p.175. In the amplifier, KT903 transistors can be used. KT909. KT912, KT930 and others. It is advisable to choose a pair with a difference in h21e of no more than 30%. The quiescent current of transistors is 200 ... 300 mA. The design of the radiator is shown in fig. 4.
(click to enlarge)
A properly assembled amplifier requires virtually no adjustment.
Since May 1990, about 20 silos have been manufactured. All of them showed good results and very good repeatability.
Author: N.N. Grigorov, Belgorod; Publication: N. Bolshakov, rf.atnn.ru
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