Acorn. Miniature glass envelope with side contacts. About the size of an acorn

Balloon envelope shape. Glass sphere or rounded top.

Classic envelope shape. Glass tube with rounded top and centre bulge.

Thin Glass Tube. Tubular glass envelope less than 25 mm diameter. Used for miniature valves.

Thin Metal Tube. Tubular metal envelope of 25 mm diameter or less. The shape of rugged WW2 American valves.

Wide Glass Tube. Tubular glass envelope of greater than 25 mm diameter.

Wide Metal Tube. Tubular metal envelope of greater than 25 mm diameter.

Side Window. Any glass envelope with a viewing window in the side. Mainly tuning indicators.

End Window. Any glass envelope with a viewing screen at one end. Typical Cathode Ray Tube design.

Co-axial. Appears as a cone with cylindrical contact rings. Used for high frequency power valves.

Pinch. The original construction method. The electrodes are held in a fishtail of glass. The wires connecting to the base pins pass through the length of the pinch.

Glass Disc. The electrodes are fixed into a sandwich of different glass types. The supports and base pin wires pass through a short glass path.

All Glass. The glass disc base has the contact pins directly moulded into it. No separate base is required.

Disc Seal (Glass). The conical structure is built using glass ring insulators bonded to the metal ring contacts.

Disc Seal (Ceramic). The conical structure uses ceramic rings as insulators. And is capable of higher operating temperatures than glass.