DH107

The Marconi DH107 is a miniature double diode-triode for superhet receivers: signal and AGC detection by the diodes, voltage amplification by the triode, all sharing one cathode. Indirect heating is 100 mA at approximately 19 V in the April 1952 sheet; archive information places it in series heater chains. Secondary 20 V does not replace the manufacturer’s approximate figure.

Maximum triode plate voltage 250 V. At plate 250 V, grid −3 V: amplification factor 70, internal resistance 58 kΩ, transconductance 1.2 mA/V. Typical operation at those voltages gives plate current 1 mA, cathode resistor 2 kΩ, plate load 0.25 MΩ. Factor 70 is not guaranteed stage gain under any load. Plate curves extend to a 500 V axis, not replacing the 250 V limit.

Unscreened capacitances: triode grid-plate 1.35 pF, plate to all except grid 2.05 pF, grid to all except plate 2.65 pF. Each diode plate to all except the other diode 2.2 pF; between diodes 0.64 pF. Diode-grid capacitances differ: d′ 0.035 pF, d″ 0.02 pF. No internal or external screening is fitted according to the sheet; screens of other double diodes are not attributed here.

B7G viewed from underneath: 1 triode grid, 2 common cathode, 3/4 heater, 5 diode d″ plate, 6 diode d′ plate, 7 triode plate. Tubular bulb. Overall length 49–55 mm, seated length 43–49 mm, maximum diameter 19 mm; ranges and maximum are distinct. Any mounting position. Microphony is described as very low, but Marconi still asks equipment design to minimize its effects.

Photos show cathode passing through the triode and between two diode plates, plus a specimen and Marconi carton. Paper wrapping and corrugated cushioning protect it; associated description gives carton side 32 mm and height 92 mm, not bulb dimensions. This illustrates miniature-tube protection. Secondary 1951/1952 dates are not arbitrarily resolved into introduction year. Documentation: Marconi’s Wireless Telegraph Company Limited, DH107, Miniature Double-Diode-Triode, April 1952, two pages including plate curves.