The PCC84 was specifically designed for cascode operation. The normal configuration was for triode one to be operated as a grounded cathode stage directly coupled to triode two. Triode two was connected as a grounded grid stage.
The triode has a smaller inter electrode capacitance than a pentode at VHF and could be made physically small. The photograph shows that within the envelope the electrodes are a small percentage of the total volume. The two triodes would be used for initial signal amplification at up to 350 MHz. The low anode voltage and relatively high current being features to ensure low noise operation. The anode dissipation was two Watts for one triode or 2.5 Watts for both triodes operating.
The triode with the top screen seen face on.
The screens with the two triodes left and right.
The thin glass tube envelope is 22 mm in diameter and excluding the B9A base pins has a length of 49 mm.
References: Data-sheet & 1040 Type PCC84 was first introduced in 1953. See also1953 adverts.