Power amplifier for KP904. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / RF power amplifiers
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When repeating the UY5DJ power amplifier [1], it turned out that the most critical node that reduces the reliability of the entire amplifier is the output stage. After experiments on various types of bipolar transistors, I had to move on to field ones.
The output stage of the broadband amplifier UT5TA (2) was taken as a basis. The circuit is shown in Fig.1. new parts are highlighted with thicker lines. A small amount of parts made it possible to mount the cascade on the printed circuit board and heatsink from UY5DJ in place of the parts and transistors of the UY5DJ amplifier. The quiescent current of transistors is 100 ... 200 mA.
pic.1
The amplifier turned out to be very stable, not afraid of high SWR. The power supply has been greatly simplified - the supply voltage of the output stage (30 - 50 volts) has not stabilized.
A low-pass filter (1] and a universal matching device (3) are installed at the output of the amplifier.
Output power at a supply voltage of 50 volts: with one KP904A transistor - 40 W, with two - 70 W.
It should be noted that individual copies of KP904 have an initial drain current of the order of hundreds of mA. In this case, in the receive mode, a small negative voltage must be applied to point 10.
pic.2
Author: E. Ivanov (RA3PAO), Russia, Tula; Publication: N. Bolshakov, rf.atnn.ru
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