I am using the Icom IC-746 transceiver for many years and suddenly it lost power. I found that one of two transistors 2SC1972 in driver was destroyed. I bought new four transistors in Serbia, but they did not have the same characteristics as the original ones, because their maximum operating frequency was only 27 MHz. I bought another three transistors from Poland, but they were the same as I bought before.




      01R       02R      03R      04R  

     

        I decided to put RD15HVF1 mosfet transistors instead 2SC1972, which required adding a smaller pertinax board with a few electrical elements and replacing a few resistors and capacitors on the PA board.




       05R  06R  07R  08R          

       

        The scheme of Polish radio amateur SP9HVW served me as a basis. This scheme proved to be an excellent solution to this problem. Several minor changes have been made to the scheme and values of electrical elements, which can be seen in the photos.

        After mounting all the electrical elements, we started with the transceiver setup. We set the current on these transistors to 450 mA (900 mA for two) and the gate voltage was 4 V. At the output on the transmitter we got a power of 100W across the all band from 1.8 to 144 MHz.


                                               09R

       
        Thanks to Pavel YT7TA and Dragan YT7XT, who helped me a lot in reparing this transceiver, because I have a lot of difficulties with smd electrical elements.