2EG4 — 1.7-Volt High-Mu Nuvistor VHF RF Amplifier
Compact metal-shell triode for grounded-cathode, neutralized VHF amplification in television and FM receiver tuners.
Overview
The 2EG4 is a high-mu Nuvistor triode designed for neutralized grounded-cathode radio-frequency amplification in the VHF tuner stages of television and FM receivers. RCA's receiving-tube manuals document the type directly, including its distinctive 1.7 V / 0.60 A heater, small interelectrode capacitances, high transconductance, operating characteristics, and design-maximum ratings.
Its principal application is as a sensitive receiving front-end RF amplifier. The Nuvistor metal-shell construction and specialized socket distinguish it from conventional glass miniature receiving triodes.
Construction, Heater, and Basing
The 2EG4 is a single triode with a cathode, control grid, and plate, enclosed in a compact metal-shell Nuvistor package. RCA specifies 12AQ basing and a dedicated Nuvistor socket; the base illustration identifies an index lug and a shortened pin to establish the proper orientation.
The 1.7 V heater is a distinctive characteristic of the 2EG4 and must not be confused with the heater ratings of other Nuvistor types having similar RF characteristics.
Intended VHF Amplifier Application
RCA describes the 2EG4 as suitable for grounded-cathode, neutralized RF amplifier service in television and FM receiver VHF tuners.
In grounded-cathode operation, the control grid receives the radio-frequency signal and the plate circuit provides the amplified output. At VHF, the grid-to-plate capacitance can create an undesired feedback path; the explicitly specified neutralized circuit arrangement addresses this interaction.
The datasheets establish the application but do not specify a universal tuned-circuit design or guaranteed overall receiver gain. Such performance depends on the surrounding tuner circuitry.
Electrical Characteristics
RCA provides two representative sets of typical characteristics and operating conditions:
These values demonstrate a high-mu receiving triode with appreciable transconductance and moderate internal plate resistance.
The figures are consistent with the triode relationship μ ≈ gₘ × rₚ: 0.009 S × 7,000 Ω ≈ 63, and 0.0125 S × 5,440 Ω ≈ 68.
The RCA sheets also give approximate control-grid voltages of −5 V at 100 µA plate current and −6.8 V at 10 µA plate current under the stated characteristic conditions. These low-current test points describe the approach to cutoff rather than a universal grid cutoff independent of plate voltage.
Design-Maximum Ratings
The 300 V plate-supply rating is conditional: RCA requires a sufficiently large plate-circuit resistor to limit plate dissipation to 1.5 W under every operating condition. It does not permit 300 V continuously at the plate electrode.
The RCA sheets state that these ratings apply at metal-shell temperatures up to 135°C.
The grid-circuit resistance limits are reproduced according to the 2EG4 sheets. Their ordering differs from the values printed for some related Nuvistor families and should be checked against the manufacturer's actual application conditions rather than silently replaced by a family-wide assumption.
Direct Interelectrode Capacitances
These capacitances are relevant to VHF tuned-circuit loading and input-to-output coupling. The grid-to-plate capacitance is especially important to the neutralized amplifier application.
The grouped input and output measurements include the electrode and shell connections identified in the manufacturer definitions.
Relationship to Other Nuvistor RF Triodes
The 2EG4's published RF characteristics are close to those of other high-mu Nuvistor tuner triodes, including members of the CW4 and DS4 families. Nevertheless, the 2EG4 is a distinct designation with a 1.7 V / 0.60 A heater and its own RCA rating table.
Similarity in RF characteristics does not by itself establish socket, heater, or full electrical interchangeability. The heater requirements and any manufacturer-specific maximum ratings must be respected.
Technical Summary
The 2EG4 is a 1.7 V / 600 mA high-mu Nuvistor triode intended for grounded-cathode, neutralized VHF RF amplification in television and FM receivers. It offers a typical amplification factor of 63–68, transconductance of 9–12.5 mA/V, plate resistance of 5.44–7 kΩ, and plate current of approximately 6.5–7 mA at its published operating points.
Its 1.5 W plate-dissipation rating, small electrode capacitances, and compact metal-shell construction characterize it as a specialized receiving-tuner amplifier rather than an audio power or transmitting tube.
