A late example of the R Type bright emitter triode. The bright emitter was phased out during 1925 in favour of the lower consumption dull emitter types. The nickel plated brass base shell was not used after 1924 and this exhibit shows the red-gold colour of phosphorus gettering. The evidence points to a 1925 valve and one probably made for replacement purposes for domestic sets. The Osram logo was used for domestic valves.
The R Type was from the beginning, in 1916, a hard vacuum valve. Hard pumping with the vacuum pumps of the day was a long process and to remove adsorbed gases from the metal parts heat was applied. This was successful but not complete. Over time, and when hot in use, gases would be released and bombard the electrodes. The use of gettering both shortened the pumping time and after the valve was sealed the getter would continue to take in gas molecules that evolved from other electrodes. Only later bright emitters were gettered.
The Osram logo is etched into the envelope but is hard to see. The nickel plated brass base shell was used up to 1924 and then replaced with the cheaper Bakelite. SeeR Type for the earlier version.
The filament strand has been coiled on the left to act as a spring. The right hand end remains straight. The etched Osram logo is visible as is the filament voltage and the R designation.
The grid is an 11 turn helix of 0.25 mm wire with an overall diameter of 4.24 mm. The nickel anode is formed into cylinder 15 mm long and 10 mm diameter.
The relative diameters of grid and anode. This valve has the last of the BBC stamps etched into the glass on the side opposite the Osram logo. This stamp was in use from September 1924 to 1927 when the practice of using the BBC stamp died out.
The balloon envelope is 45 mm in diameter, and excluding the B4 base pins is 92 mm tall.
References: 1003, 1004 & 1005. Type R Type was first introduced in 1916.