The CV1219 is an audio power valve. The prototypes were the M-OV DA100 and the Mullard MZ1-100. The old service code was NT36.
The high voltages employed require the use of ceramic supports as can be seen above the pinch. The anode is carbonised to better radiate heat. The springs on the top mica grip the shoulder and anchor the electrodes securely. The broad up arrow denotes UK government property.
The additional insulation on and under the top mica is ceramic. The filament tension springs have hooks at the base into which the loops of the oxide coated filament ribbon sit. The plated grid wire passes straight across the face of the anode. The distortion seen is due to the glass. Note that in the centre of the anode working face is an additional heat sinking flange.
From the top it can be seen that the main top support is ceramic with the mica disc having its major role in holding the electrodes firm in the envelope.
The base ceramic support: the preformed grid is spot welded to the leads emerging from the pinch.
The classic envelope is 65 mm in diameter and, excluding the L4 base pins, is 171 mm tall.