valved transmitter for 3.5 MHz


Posted on Feb 7, 2014

This transmitter project is a highly efficient, rugged and simple, low power c. w. unit delivering more than 10W. As it`s crystal controlled with stabilised h. t. , and a buffer stage between the crystal oscillator and power amplifier stages, it produces an exceptionally clean c. w. performance. Many amateurs will have some, if not all, of the necessary parts. However,


valved transmitter for 3.5 MHz
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some components are readily available from advertisers of surplus or new components, and other sources such as rallies. The project uses a simple circuit as the transmitter uses valves. All the valves used are readily available, and can be overrun and abused - unlike many transistors! If the valves fail, you just pull them out and plug in a replacement. Remember that valves which were designed before the Second World War are still in use, so they must be considered reliable and worthy of use. The two separate units are interconnected with a cable and plug socket assembly. This is done so that the power supply unit (p. s. u. ) can be used with other equipment. However, the circuits and layouts I`m describing can be amalgamated into one chassis/cabinet to provide a complete transmitter with integral power unit. The dimensions are not critical. Practically speaking, any suitable chassis/cabinet(s) can be used for the project. No real attempt at miniaturisation was made. The object was reliability, making it easy to build and easy to service. Conventional, well tried and tested circuitry has been used throughout. Signal strength with stability, quality and reliability was my target. The good quality of the resulting c. w. signal has been remarked on by other stations during QSOs. Any a. c. existing p. s. u. providing 250-300V d. c. at 100mA, plus a 150V stabilised supply would be suitable. Two 6. 3V heater windings of at 15 amp...




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