The 5726 is a miniature all glass premium quality pair of signal diodes. The design was for detector service in wide band equipment. This would typically be RADAR. The premium version is designed to be used in areas of shock and vibration such as aircraft equipment. The UK government procurement code is CV4007.
The domestic version of these diodes was the 6AL5 and here the use was television video detector. The two diodes are completely separate almost flat structures separated by a flat metal screen.
One of the diode sections. The valve is marked Made in England.
The paper logo of Brimar T for trustworthy valves. What did this logo say about their commercial range?
The thin glass tube envelope is 18 mm in diameter, and excluding the B7G base pins is 36 mm tall.
Reference: Datasheet. Type 5726 was first introduced in 1952.