100W AM Valve RF Transmitter circuit
Posted on May 3, 2017 8085
The coils L2 and L3 as shown in the drawing are inductively coupled and are constructed as follows. On a 5 centimeter cylinder, wrap 140 coils with 0.5 millimeter enamelled copper wire, which will form the L3 coil. On 70 coils we place a medium shot and then ground it. Then, over the layer of L2, wrap with 0.5 mm thick wire, 50 coils that will form the L2 coil. The variable air capacitor C2 is 1000pF and must be isolated from the chassis because both reinforcements are of high voltage as shown in the figure. The coils L4 and L5 are also inductively coupled and manufactured as follows. On a 8 centimeter diameter roller, wound with 1 mm diameter enamelled copper wire, 70 coils a little sparse with each other. This coil is L5 wrap 100 spools with 1 mm diameter wire. In the 50th coil we place a middle T coil. This is the L4.
The variable capacitors C3 and C4 are a double coaxial air (500 + 500pF) with sparse sheets to avoid sparks. We need to isolate it from the chassis because it has a high voltage in both armatures. An E1 indicator lamp is used in order to be tuned in to the antenna. The low-frequency amplifier has three inputs (for both microphone and two other audio sources). The R2 potentiometer serves to adjust the volume of the voice or music of inputs A and B. R1 and R2 (if used) are the mixing system. The transformer has a primary to secondary ratio of 2. The primary resists up to 80mA. The configuration is made by the protective grid with its secondary modulation transformer.
If the transmitter amplifier is used to receive loudspeakers then use the Transformer with Data (AD9047 from PHILIPS) for a loudspeaker transformer. If you want, you can use this transformer to configure the transmitter despite all the few ohms that it has on the secondary (16Ω).
The power supply that uses the 5U4 feeds the entire amplifier and the 6V6 oscillator. Its transformer is: primary 220V, secondary 2 x 400V for 200mA, 6.3V and 5V. The power supply that uses the 5R4 feeds the BUFFER 807 and the other two 807. This power adapter is: primary 220V, secondary 2 x 750V for 250mA, 6.3V, 5V. Switch D1 serves to move from broadcast to reception and vice versa. This transmitter with a good antenna (mostly long in length) can be heard too far.