3V power supply 2 tube FM microphone

One of the two transistors is used for audio amplification, and the other is a high-frequency oscillator tube and frequency modulation tube. VT1 (9013) constitutes the first-stage audio amplifier, which amplifies the audio signal output by the electret microphone and couples it to the base of the high-frequency oscillator tube VT2 through capacitor C2. The frequency of the high-frequency oscillator circuit is adjusted to the 88-108MHz FM broadcast band, which is convenient for debugging with FM radio. This frequency is adjusted by the LC resonant circuit L1 and C4, and the audio signal sent by VT1 will frequency modulate this frequency. When the audio signal is coupled to the base of VT2 through C2, the oscillator frequency will continuously change with the audio signal, generating the required FM frequency modulation signal, which is transmitted through the antenna. The FM microphone circuit composed of simple transistors and other discrete components:

Use a high-sensitivity electret microphone for the microphone MIC, with the outer shell connected to the negative terminal. Use either the 9013 or 9014 with a higher amplification factor for VT1, and a high-frequency tube such as the 3DG130 or 9018 for VT2. The L1 oscillator coil is made of 0.71mm enameled wire wound densely on a 3mm round rod with four turns. Use a 1m flexible wire for the antenna, with a transmission range of approximately 200m. The circuit draws approximately 5mA in normal operation.