Subminiature CV4501 tube (SQ version of EF72), 35 mm extended × ten mm diameter (excluding leads) Early tubes made use of a metallic or glass envelope atop an insulating bakelite foundation. In 1938 a way was produced https://blog.globalgoodsguru.com/pu-sealants-for-automotive-applications-enhancing-vehicle-performance-affb2479a44a