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 gasses 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.
This exhibit from BTH has an intact filament.
The nickel plated base has an A stamped on it to indicate the anode. The pins are of two part construction with the lead-out wires soldered to the top of the pins.
The underside of the base showing the composition in-fill to the metal shell. The centre of the base has the BTH logo. The pins appear to be un-scratched and suggests that this valve has not been used.
The anode cylinder with grid within.
Here the folder and crimped fixing for the filament can be seen on the right.
The balloon envelope is 37 mm in diameter, and excluding the B4 base pins is 83 mm tall.
References: Private communication, 1005 & 1003. Type R Type was first introduced in 1916. See also1916 adverts.
