2CW4 — High-Mu Nuvistor VHF Amplifier Triode

Compact metal-shell triode for grounded-cathode, neutralized RF amplification in VHF television and FM receiver tuners, with a low-voltage 450 mA heater.

Overview

The 2CW4 is a high-mu Nuvistor triode designed for grounded-cathode, neutralized radio-frequency amplification in VHF tuners of color and black-and-white television receivers and FM receivers. RCA identifies it as electrically corresponding to the 6CW4 and 13CW4, with different heater requirements. The 2CW4 uses a 2.1 V, 0.45 A heater, distinguishing it from the 6.3 V and 13.5 V family members.

The RCA and Sylvania documents describe a small metal-shell receiving triode combining high amplification factor, relatively high transconductance, and low interelectrode capacitance. These properties support its explicitly specified use in high-frequency tuner input stages.

Construction and Heater

The 2CW4 uses Nuvistor metal-shell construction and a dedicated Nuvistor socket. Sylvania identifies a medium ceramic-wafer, five-contact Nuvistor arrangement with 12AQ basing and a maximum overall height of approximately 0.800 inch, seated height of 0.625 inch, and diameter of 0.440 inch.

The Sylvania family table rounds the heater voltage to 2.0 V, whereas RCA's individual 2CW4 entry and family table specify 2.1 V at 450 mA. The precise manufacturer's heater condition should be retained when comparing published data.

Intended RF Applications

RCA describes the CW4 family as neutralized grounded-cathode VHF RF amplifiers for FM broadcast receivers, color television tuners, and black-and-white television tuners.

The control grid receives the RF signal relative to the cathode, and the plate provides the amplified output. At VHF, feedback through grid-to-plate capacitance becomes an important design consideration; the specified neutralized configuration addresses unwanted coupling between input and output circuits.

The manufacturer sheets do not give a single universal tuner gain or frequency-response figure for all installations. Those depend on the tuned input and output networks and the circuit's neutralization.

Electrical Characteristics

RCA publishes two representative sets of Class A1 characteristics:

The amplification factor and transconductance place the 2CW4 among high-mu, high-slope receiving triodes. The published values satisfy the approximate triode relationship μ = gₘ × rₚ: 0.0098 S × 6,600 Ω ≈ 65, and 0.0125 S × 5,440 Ω ≈ 68.

The RCA data also list approximately −4 V control-grid voltage for a plate current of 10 µA at the stated measurement condition. This is a characteristic test point, not a universal grid-cutoff voltage independent of the plate circuit.

Maximum Ratings and Manufacturer Differences

RCA gives the following Class A1 design-maximum ratings:

The 300 V plate-supply limit applies only with a sufficiently large plate-circuit resistor to keep dissipation within the specified limit at every operating condition; it is not an unrestricted 300 V plate-electrode rating.

Sylvania lists 1.0 W maximum plate dissipation in its family table, whereas RCA lists 1.5 W. This is a genuine published rating difference that should be preserved rather than resolved by choosing the higher figure without qualification. RCA specifies operation at metal-shell temperatures up to 135°C under its stated rating conditions.

Interelectrode Capacitances

RCA and Sylvania give approximate capacitances for the Nuvistor family:

RCA gives 1.6 pF heater-to-cathode capacitance, while Sylvania's shielded-capacitance table lists 1.3 pF. Measurement context and manufacturer should be considered when using these values.

The grid-to-plate capacitance is especially relevant to the neutralized amplifier application. The published grouped input and output capacitances include the metal shell and other electrodes named in their measurement definitions.

Related Types and Heater Selection

RCA explicitly identifies these as related high-mu Nuvistor triodes with different heater ratings. Their signal-electrode characteristics may correspond, but the heater supplies are not interchangeable without circuit changes.

Technical Summary

The 2CW4 is a 2.1 V / 450 mA high-mu Nuvistor triode for neutralized grounded-cathode VHF RF amplification in television and FM tuners. Its typical amplification factor is 65–68, transconductance 9.8–12.5 mA/V, plate resistance 5.44–6.6 kΩ, and plate current approximately 7 mA at the documented operating points.

The compact metal-shell Nuvistor construction, small interelectrode capacitances, and specialized tuner application distinguish it from ordinary audio-frequency receiving triodes. Its manufacturer-specific maximum plate-dissipation ratings require attention, and its heater specification distinguishes it from the 6CW4 and 13CW4.