EA50

The EA50 is a small indirectly heated diode for signal detection. Philips’s April 25, 1939 sheet describes detection in television receivers; Mullard retains this primary application. Construction is recognizable by its slender glass envelope and terminal arrangement: anode at one end, three aligned wires at the other, two heater wires and a central cathode. There is no amplifying control grid: the documented function is signal conversion through diode detection.

The nominal heater requires 6.3 V and 0.15 A; Philips permits AC or DC and parallel supply. Stated anode-cathode capacitance is 2.1 pF. Detection curves show output depending on RMS radio-frequency signal and load resistance, with families for 2 kΩ, 5 kΩ, 10 kΩ and 0.5 MΩ. There is no universal load-independent EA50 output voltage. Small test-circuit capacitors are also part of the conditions: consulted sheets do not all use the same value, and no unstated guaranteed bandwidth is derived from them.

Edition limits must be read separately. Philips 1939 prints Vd maximum 200 V and current maximum 5 mA; the two Mullard sheets print Va or Vd maximum 50 V and again 5 mA, with heater-cathode maximum 50 V and maximum external resistance 20 kΩ. Philips’s November 11, 1953 edition explicitly distinguishes maximum peak inverse voltage 560 V, maximum average current 5 mA, maximum peak current 30 mA and maximum cathode-heater difference 100 V, retaining external resistance 20 kΩ. Peak inverse voltage must not be treated as the same quantity as the earlier Va or Vd entries.

Philips’s 1939 practical note specifies soldering directly into the wiring and warns against overheating terminals, which could crack glass-to-metal seals. Archive photographs also show specimens with a holder and spring anode contact: observable constructions, not grounds for ignoring wire identification. Drawings identify the central wire of the three as cathode, side wires as heater, and isolated opposite terminal as anode. A top connection must not be confused with the grid of other tubes.

Philips 1953 and Mullard 1839/1 drawings give maximum diameter 12 mm and maximum overall length 69 mm, including drawn terminals. Mullard 1546/1 Issue 2 instead gives maximum overall length 49 mm, still maximum diameter 12 mm: separate drawings, not dimensions to average. Philips 1939 additionally distinguishes maximum width 13 mm at the lower glass region. Glass-body length cannot be obtained by blindly subtracting maximum terminal lengths from maximum overall length. Documentation: Philips Miniwatt, EA50, April 25, 1939, two pages; Philips, EA50, November 11, 1953, data and characteristic sheets; Mullard, EA50 Television Diode, 1839/1–2; Mullard, EA50 Miniature Diode, 1546/1–2, Issue 2. Dates belong to sources, not to manufacture of every specimen.