The paper describes a system forming a precise nuclear quadrupole resonance (NQR) thermometer based on the resonance line of35Cl in KClO3. The system includes a transistorized Robinson oscillator for the detection of the NQR absorption signals. Details of the oscillator design are given and the method of detection of the NQR absorption signals through frequency modulation is described. The oscillator is locked to the NQR absorption line through a feedback loop including a phase sensitive detector. Conversion of frequency modulation to amplitude modulation in the amplifier section is partially avoided through the use of a second feedback loop which locks the amplifier tuning frequency to the oscillator frequency. An accuracy of the order of 0.003°C in temperature determination at liquid nitrogen temperature is obtained.