300kHz Signal Generator

As shown in the figure, it is a 300kHz signal generator. It is composed of VT1, T1, VD4 and related components to form a voltage-controlled oscillator. The voltage-controlled oscillator adopts LC collector tuning. VTl is an oscillator tube. The tuning circuit is composed of variable capacitance diode VD4, capacitors C3~C6 and the inductance of the 1~3 windings of the variable capacitance diode T1. The variable capacitance diode VD4 works in reverse bias, and the control voltage is added to the negative end to change its capacitance. The oscillation signal is output by the 6~7 windings of Tl. Among them, C6 is a frequency fine-tuning capacitor. VD3 stabilizes the working voltage of the oscillation stage, and the stable voltage is 6.8V±0.2V.

Component selection:

Transistor VT1: 3DG6C, β=65～85.

Diodes VD1, VD2: 2CPl4, VD5: 2CK18.

Zener diode VD3:2CWl4.

Varactor diode VD4:2CC5.

Resistors R1: 3.6k, R2: 3.3k, R3: 5.1k, R4: 510Ω, R5: 3.9k, R6: 3k, R7: 100k, all of which are RTX-0.125W.

Capacitors C1, C2: 5μF30V, C3: 51pF100V, C4: 820pF100V, C5: (optional during commissioning), C6: 20pF. Transformer T1: Model L22, A=100.

L1-4: Φ0.29mm, 27 turns, L2-3: Φ0.29mm, 18 turns, L4-2: Φ0.29mm, 9 turns, L5-8: Φ0.29mm, 7 turns, L6-7: Φ0.29mm, 6 turns.

L1-3=292μH, allowable error range: 0～10μH.