The 6B7 is for parallel heater based mains receivers. The 2B7 differs only in that it has the original American standard AC heater of 2.5 Volts.

The pentode could be used as the final IF amplifier with the diodes as detector and AGC rectifier or it could be used with the pentode as first AF amplifier. The vari-μ nature of the pentode suggests use as an IF amplifier as does the control grid connected to the top cap.