Signal level control circuit for amplifiers

An amplifier (125) includes a gain stage (210) for amplifying a signal, a variable attenuator (208), such as a Bode circuit, coupled to the gain stage (210) for attenuating the signal, and a signal level control circuit (222, 218, 220) coupled to the variable attenuator (208) and the gain stage (210) The signal level control circuit includes a thermal circuit (218) for measuring a temperature and a removable automatic gain control (AGC) circuit (220) for measuring signal level output by the gain stage (210). An adapter (222) coupled to the thermal circuit (218) and the removable AGC circuit (220) for controlling attenuation of the variable attenuator (208) in response to the temperature when the removable AGC circuit (220) is not electrically coupled to the gain stage (210) and in response to the signal level when the removable AGC circuit (220) is electrically coupled to the gain stage (210).