The type 27 triode is also known as the UY-227. It is an indirectly heated audio valve with a good reputation for performance. The heater rating at 2.5 Volts was the original American standard for indirectly heated valves before the introduction of 6.3 Volts in the mid 1930s.
With 90 Volts on the anode the grid bias should be -4.5 Volts. At 135 Volts on the anode the bias should be -9 Volts. At the absolute maximum anode voltage of 180 Volts the bias should be set to -13.5 volts. The heater cathode voltage should not exceed 9 Volts.
The anode side flanges serve to form a place to stitch the plates together as well as providing fixings and additional heat dissipation.
The UX5 base pins.
The top mica with the two hairpin heater loops emerging from the top of the cathode tube.
The pinch and lower mica.
The classic envelope is 38 mm in diameter, and excluding the UX5 base pins is 88 mm tall.
References: Datasheet, 3002, 1043 & 1040. Type 27 was first introduced in 1935.