The M-OV type R5V was a landmark valve in that it was the first British high-vacuum receiving valve to incorporate a sprung 'inverted V' filament of the type which later became universal. The inverted V sprung filament had been used in transmitting valves as had the flattened anode.
As far as we know all R5Vs were gettered to ensure a high vacuum and allow use with up to 120 V on the anode. This, and its (relatively) low Ra value (30,000 ohms) enabled the R5V to provide sufficient audio power to operate a horn loudspeaker at (just) acceptable volume (tens of milliwatts).
The paper strip label on this exhibit gives the filament current as 0.7A. In later versions of this valve the current was reduced very slightly to 0.66A in order to match that of the Type R. Type R5V was successful both technically and commercially. Like the type R it remained listed until the outbreak of WWII and many samples survive.
The R5V from Marconi-Osram was a general purpose valve, similar to the original R-type, and made from the early 1920s in considerable quantity. The differences from the R-type were a lower anode resistance and the 5.0 V filament but it is still a bright emitter.
This valve has the type one BBC stamp. This stamp was used from 1st November 1922 until September 1924 and thus this exhibit can be accurately dated.
The paper label gives the operating conditions without the grid bias value. The Marconi name is etched into the glass.
The flattened anode with round ends and within the grid wires are parallel to the flat face of the anode.
Here the filament tension spring can be seen on the left.
A slightly clearer view of the Marconi Valve logo containing the fact that it was made at te Osram works.
The balloon envelope is 46 mm in diameter and, excluding the B4 base pins, is 94 mm tall.
References: 1005. Type R5V was first introduced in 1922.