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.
For a low cost set for local reception a pentagrid converter the 6B7 and a high sensitivity output valve would be the probable line-up.
One of diodes forms the bright box seen below the screen around the pentode. The other diode is the pair of vertical rods.
The diodes forming the second diode are clearer in this picture. The insulated heater is in the centre. The wire grids can just be seen at the top of the image.
The clasic envelope is 37 mm in diameter, and excluding the UX7 base pins is 98 mm tall.
References: Data-sheet & 1040. Type 6B7 was first introduced in 1932.