The 6U5 = 6G5 is an American design of Magic Eye tuning indicator. The display is green in colour and is of the form of a partial disc. The stronger the signal the more the disc tends towards solid green.
This exhibit is from Tungsram and they call the device a Tunoscope in the lettering on the glass under their name.
The triode amplifier sits below the display bowl or target. The deflecting electrode, connected to the triode anode, can be seen to the left of the cathode.
A closer view of the electrodes. The cathode tube is coated only within the triode and again within the display.
The deflector electrode is the bright plate below the display cathode.
The type of display produced.
The wide glass tube envelope is 29 mm in diameter and, excluding the UX6 base pins, is 87 mm tall.
References: Datasheet, 3002, 1043 & 1040. Type 6U5 was first introduced in 1937.