British Type "A" Tube
|The British type "A" tube
was introduced in 1917 by the British Thompson-Houston (B.T.H) Company.
This tube may have been designed for use in low power transmitters.
The notch in the press visible in the second photograph was typical of
tubes designed for operation at high voltages, and the double-cylinder
plate may have been an attempt to increase the surface area for better
Unfortunately, the tube shown here has been damaged. The internal elements are out of position, and the tube has lost its vacuum, which explains some of the discoloration inside the bulb.