EA76

The EA76 is an indirectly heated subminiature single diode for detection and rectification of radio-frequency and intermediate-frequency signals. Its heater requires 6.3 V at 150 mA. Size is a distinguishing feature: Mullard’s drawing allows a maximum diameter of 5.4 mm and body length up to 28.5 mm, with connection wires emerging directly from the glass. The arrangement is B5B/F. Unlike a conventional miniature socket-mounted diode, its flying leads allow direct incorporation into a circuit.

Retained Mullard advertisements place the EA76 in the transition from miniature to rugged subminiature valves. A Wireless World page from April 1950 includes it in the range for communications and industrial equipment. Another, from January 1953, announces indirectly heated subminiatures as soon available commercially and recalls development for service applications including guided missiles and fire-control systems. These document presentation of the range; they do not prove that every EA76 served in such equipment or alone establish one introduction date.

Mullard’s issue-4 datasheet separates limits that summaries may blur: maximum peak inverse voltage 420 V, maximum anode voltage 150 V, maximum anode current 9 mA and peak anode current 54 mA. It also gives 330 V peak between heater and cathode with the cathode positive. The conduction graph shows current versus anode voltage but does not replace these limits. Capacitances are specified for shielded and unshielded mounting: anode to cathode-plus-heater capacitance is respectively 4.0 and 3.1 pF, relevant to signal circuits.

Mounting instructions are important. Any operating position is allowed, but direct solder joints must be at least 5 mm from the glass seal and wire bends at least 1.5 mm away. Mullard also warns that the small body may become very hot and suggests a metal clip conducting heat to the chassis. Photographs of the Mullard-marked specimen show a bright anode with side flanges and the cathode passing through its rectangular opening. Small dimensions therefore do not remove the mounting’s mechanical and thermal requirements.