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Superconducting receivers based on large hot electron bolometer (HEB) bridges were constructed and they show low noise temperatures. Their stability has been characterized by the Allan variance measurements with either far-infrared laser or Gunn oscillator plus multiplier chain as the local oscillator. An Allan time of about 1 s has been obtained. Also demonstrated is the effectiveness of a stabilization scheme in which a radiation at a frequency much lower than the gap frequency of niobium nitride is used for improvement.