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The R Type was from the beginning a hard vacuum valve. Hard pumping with the vacuum pumps of the day was a long process and to remove adsorbed gas 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. Here we have a beautiful, and rare, red-gold colour that is the result of using phosphorus as the getter. Only later bright emitters were gettered and this example is probably from 1923 or 1924.

The Marconi Osram Valve 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. See R Type for the later version.

Thanks to Joe Gruber for sending the images.

The balloon envelope is 45 mm in diameter, and excluding the B4 base pins is 97 mm tall.

References: Private communication, ¹⁰⁰⁵ & ¹⁰⁰³. Type R Type was first introduced in 1916. See also 1916 adverts.

Pin Connections

Absolute Maximum Operating Conditions^¶