EA52

The EA52 is an indirectly heated measuring diode for frequencies up to 1000 MHz, or 1 GHz, according to Philips and Tesla data sheets. Its small glass envelope encloses a disc-seal construction: the anode ends in the upper axial contact, the cathode in the annular disc, and the heater in two flexible lower wires. This arrangement differs from a numbered-pin base and forms part of its high-frequency measuring construction. Stated anode-cathode capacitance is below 0.5 pF. Tesla lists the American 6923 as a corresponding type: a manufacturer’s indication that still calls for checking characteristics and mounting.

The nominal heater requires 6.3 V and 0.3 A. Philips permits AC or DC, series or parallel supply and specifies a 5.6–7.0 V range. Characteristics give diode current 0.5 mA at less than 3 V; this characterization point must not be confused with the average-current limit of 300 µA, or 0.3 mA. The ordinary maximum peak current is 5 mA. Below 100 Hz, the 1962 Philips sheet gives a specific peak limit: 0.3 + 0.047 f mA, with f in hertz. Average and peak currents remain separate quantities.

Inverse voltage also depends on frequency. The sheets allow maximum peak inverse voltage 1000 V below 100 MHz; above this frequency the limit becomes 1000 × 100/f V, with f now in megahertz. The 1000 V rating therefore cannot be extended over the whole range to 1 GHz. Maximum cathode-heater difference is 50 V and external resistance between them is limited to 20 kΩ. Philips frequency-response curves specify a 1 MΩ load; Tesla also supplies detector efficiency and input-resistance curves at 40 MHz for several loads. These test conditions help interpret diode behavior, rather than guaranteeing circuit-independent accuracy.

Mounting requires care with glass-to-metal seals. Tesla specifies bending wires more than 2 mm from the seal and soldering more than 7 mm away; the spring clamp also connects the cathode. Philips recommends a spring contact that avoids stressing the glass and, in the 1959 and 1962 editions, limits cap temperature to 100 °C. Finishes vary by edition: Philips describes cadmium-plated heater wires in earlier drawings and gold-plated wires in 1962, whereas Tesla describes a gold-plated anode contact. The same finish cannot therefore be assigned indiscriminately to every terminal and specimen.

Drawings give disc diameter 15 ± 0.1 mm and maximum dimension 42.5 mm from the anode tip to the lower glass tip, excluding the long flexible heater wires. Maximum upper-body diameter is 12 mm in Philips 1957 and Tesla 1960 drawings, but 11.2 mm in Philips 1962; Tesla also specifies maximum mass 6 g. Dimensions remain tied to manufacturer and edition. Documentation: Philips, EA52, sheets dated May 5, 1957, September 9 and October 10, 1959, December 12, 1962, with drawings and curves; Tesla, EA52, December 12, 1960, four pages. These dates identify documents, without establishing the type’s introduction or the manufacture dates of photographed specimens.