6E8G

The 6E8G combines a triode and hexode for frequency conversion in radio receivers. The triode serves as oscillator, while the hexode receives the radio signal and performs conversion; the triode grid is internally connected to hexode grid 3. Preserved photographs show green-coated Mazda examples and a gold-coated Tungsram marked Made in France. The registration data examined instead come from J. Visseaux, Lyon, a sheet dated May 30, 1939 and RMA registration 188A of June 2, 1939. These document dates are distinct from secondary references to introduction in 1938.

Heater rating is 6.3 V, 0.3 A, AC or DC. Converter limits are hexode plate 250 V, hexode screens, grids 2 and 4, 100 V, triode plate 200 V, total cathode current 15 mA. The hexode control-grid entry is labelled minimum voltage −2 V. Much more negative biases are separately given for very low conversion transconductance; those conditions must not be confused with the nominal operating point.

The upper-voltage conversion point uses hexode plate 250 V, screens 100 V, control grid −2 V; triode plate 150 V, grid resistor 50 kΩ. Conversion transconductance is 650 µmho, or 0.65 mA/V, hexode plate resistance approximately 1.25 MΩ. Listed currents are hexode plate 3 mA and screens 3 mA, triode plate 5 mA and grid 0.2 mA; cathode bias resistor 190 Ω. Approximately −22 V control-grid bias reduces conversion transconductance to 2 µmho.

Further points use a 100 V hexode plate. RMA 188A specifies screens 70 V, grid −1.5 V, triode plate 100 V, conversion transconductance 450 µmho, hexode plate current 1.25 mA and screen current 2.25 mA, cathode resistor 220 Ω. The earlier Visseaux sheet instead gives 60 V screen voltage at this point; each value remains assigned to its version. The triode alone, not oscillating, gives approximately 2800 µmho at plate 150 V, grid 0 V. This is not the combined converter’s conversion transconductance.

The source distinguishes approximate RF input capacitance 5.2 pF, oscillator input 9 pF, oscillator output 4.5 pF and mixer output 10.5 pF, with electrode exclusions specified in the sheet. Direct coupling capacitance between hexode signal grid and plate is of the order of 0.003 pF. These figures explain the two-section arrangement without inventing receiver bandwidth or gain not specified by the documents.

Octal basing 8O: heater 2 and 7, hexode plate 3, hexode screens 2 and 4 at pin 4, triode grid and hexode grid 3 at pin 5, triode plate 6, common cathode 8; hexode signal grid at the top cap. Pin 1 has no connection drawn. RMA drawing maxima: bulb diameter 1 9/16 inches (39.6875 mm), base outline 1 5/16 (33.3375 mm), overall height including cap and key 4 13/32 (111.91875 mm), body height without cap or pins 3 15/32 (88.10625 mm). These are not measurements of the photographed examples. Documentation: J. Visseaux, 6E8G, Triode-Hexode Converter, May 30, 1939; Radio Manufacturers Association, Registration 188A, June 2, 1939.