Valve Transmitter circuit 70W

This transmitter with a good antenna and under proper conditions of use may have a range of more than 45km. The configuration is made by the rise of the output lamp, which makes it advantageous as regards the fidelity of the emitted signal. The 6V6 lamp is used in the oscillation step. The coil L1 will be commercially available as a 6SA7 oscillator. Intermediate reception of L1 is associated with the 6V6 cathode. In the isolation stage, the 6L6 (Buffer) lamp is used. Coil L2 consists of 40 coils of 0.3 mm thick enamelled wire wound into a 4cm diameter drum. The L3 coil, which has 60 coils of the same wire, is also wound on the same drum. The E151, high relative power lamp is used in the output stage. Coil L4 consists of 50 coils of 1.2 mm thick enamelled wire wrapped in a 5cm diameter drum. The coils of all coils must be welded.
Valve Transmitter circuit 70W - schematic

The variable capacitors C1 and C2 will have their sheets thin Also their insulations will be made of porcelain. The capacitor C3 works at 2kV. All RFCs have an inductance of 2.5mH ​​and can pass a current of 100mA. Transformer T1 has a 8K impedance primary. Insulations must be made for a voltage of 1kV.

Transformer T2 works with primary 220V, as secondary has three windings: A winding for 6,3V, one for 5V (supplying 5R4) and one for high voltage 2X750V, 100mA. 750V filter capacitors have a capacity of 100μF and operate at 450V. They are connected in series and operate at a voltage of 1200V.

At the ends of each elementary capacitor a resistance 100k is connected to stabilize the voltage of the capacitor. Supply of the isolator, oscillator, and modulator preamplifiers is provided by the mains voltage through a silicon rectifier (D) operating at 250V and a current of 200mA.

All resistors other than those listed in the drawing are 1W power. All capacitors except those listed in the drawing operate at a voltage of 300-400V. Once the antenna is in place and is connected to the transmitter, for maximum signal output and range, set the instrument to indicate the minimum indication.

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