The UABC80 is a triple diode triode in a miniature envelope. This example is a British Made Mullard valve.
The UABC80 and its 300 mA brother PABC80 were specifically designed for use in the detector stage of early FM and FM/AM radios. Normally this valve featured in a ratio detector circuit for FM demodulation and a diode detector for AM as well as the first stage of audio amplification.
It can be seen in the photograph that three separate valves exist within the envelope. The triode is on the right, the single diode on the left. In the middle is the double diode, with the central box an the anode for d(1) and the anode for d(3) being a rod within the central box.
The three heaters are connected in series. The two metal strips seen on the left in the picture take the connections from pins 4 and 5 to the top of the valve. All heaters enter from the top.
The heater connecting strips are on the left and above the top mica can be seen the insulated heater wires.
The distinctive three boxes of the xCH80 series.
The thin glass tube envelope is 20 mm in diameter, and excluding the B9A base pins, is 59 mm tall.
References: Data-sheet, 3002 & 1040. Type UABC80 was first introduced in 1952.