The VU29 is a half wave mercury vapour rectifier with the Type designation indicating an RAF valve made before 1941 when the designations changed to the CV register.
The PIV is 10 kV and the average forward current is 600 mA.
The Am and Crown for the UK Air Ministry. The GES brass base is badly corroded but the valve came in the original unopened box with wadding wrapped round the envelope. The screw top cap dates this valve to the early 1930s.
The disc anode and the zigzag filament.
The top cap and the domed disc anode.
A closer view of the filament with spots of mercury.
Serial number on the pinch reads 2093.
Most of February 2025 was taken up preparing a talk for the local U3A. This outlined the journey from classical to modern physics showing the critical developments such as Faraday - the induction coil, Sprengel - the vacuum pump, cathode-rays, the Braun tube, J J Thompson and finally to Niels Bohr and an explanation of spectra. The VU29 required 32 Volts to initiate the discharge and then ran with 16 Volts across the tube. A DC-DC converter dropped 19 Volts to the 4 Volts 9 Amps for the filament.
A closer view without other illumination in the light box.
With a little white light in the box.
The spectrum of low pressure mercury vapour.
The wide glass tube envelope is 57 mm in diameter, and including the GES base is 210 mm tall.
