2DS4 — Extended-Cutoff High-Mu Nuvistor VHF Triode

An indirectly heated, 2.1-volt Nuvistor RF amplifier triode for neutralized grounded-cathode operation in television and FM tuners.

Overview

The 2DS4 is a high-mu Nuvistor triode with extended-cutoff characteristics, intended for VHF radio-frequency amplification in television and FM receivers. RCA identifies the 2DS4 as the low-voltage-heater version of the 6DS4, with the same signal-electrode characteristics except for heater ratings. Its specific receiving application is a grounded-cathode, neutralized RF amplifier in color or black-and-white television tuners and FM receiver front ends.

The extended-cutoff designation in RCA's technical data distinguishes the DS4 family from an otherwise similar general-purpose high-mu triode. Its published grid-voltage-versus-plate-current test points describe the approach to low plate current at increasingly negative grid bias.

Construction, Heater, and Physical Form

The 2DS4 uses a metal-shell Nuvistor structure and a dedicated Nuvistor socket. Sylvania describes a ceramic-wafer five-contact arrangement, E5-65, with 12AQ basing. The published maximum diameter is 0.440 inch and maximum seated height 0.625 inch; the listed overall height is approximately 0.600 inch in the Sylvania extract, so mechanical clearances should be checked against the actual outline drawing.

The heater rating is a principal difference from the 6DS4, which uses a 6.3 V heater drawing approximately 0.135–0.138 A in the published references. RCA's dedicated 2DS4 entry also specifies the 450 mA heater with a tolerance of approximately 30 mA.

VHF RF Amplifier Application

The manufacturer specifies grounded-cathode, neutralized VHF amplifier service. In this arrangement the RF input drives the grid relative to the cathode, while the output is developed in the plate circuit. Neutralization is relevant because the tube's finite grid-to-plate capacitance couples some output signal back toward the input.

The documentation explicitly names FM receivers, color television receivers, and black-and-white television receivers. It does not identify the 2DS4 as an audio power tube or a transmitter output tube.

Typical Electrical Characteristics

The RCA and Sylvania data provide two representative operating conditions:

The figures reflect a high-mu, relatively high-transconductance receiving triode. The relationship μ ≈ gₘ × rₚ is consistent with both conditions: 0.009 S × 7,000 Ω ≈ 63, while 0.0125 S × 5,440 Ω ≈ 68.

Extended-Cutoff Behavior

RCA specifies approximate grid voltages of −5 V at 100 µA plate current and −6.8 V at 10 µA plate current under the stated characteristic test conditions. These values characterize the low-current region of the tube's transfer behavior. They should not be treated as universal cutoff voltages at every plate voltage or load.

Maximum Ratings

RCA publishes the following Class A1 design-maximum limits:

The 300 V plate-supply allowance requires a sufficiently large plate-circuit resistance to keep dissipation within its stated limit under all operating conditions. RCA also specifies the ratings for metal-shell temperatures up to 125°C.

Sylvania's design-maximum table lists a 1 W plate-dissipation limit rather than RCA's 1.5 W. This manufacturer difference should be preserved and the appropriate document consulted for the actual tube and equipment.

Interelectrode Capacitances

The RCA and Sylvania tables give approximate direct capacitances:

These capacitances influence the tuning, loading, and feedback behavior of the specified VHF RF amplifier. The relatively small but nonzero grid-to-plate capacitance is especially relevant to neutralized operation.

Relationship to the 6DS4 and Other Nuvistors

The 2DS4 and 6DS4 are explicitly described by RCA as equivalent in their signal-electrode characteristics except for the heater. The 2DS4 uses 2.1 V at 450 mA, while the 6DS4 uses 6.3 V at approximately 135 mA.

The DS4 family is also related in general application to the CW4 high-mu Nuvistor RF amplifier family, but the RCA documentation separately identifies the DS4 as having extended-cutoff characteristics. That distinction should not be erased by treating every Nuvistor VHF triode as electrically identical.

Technical Summary

The 2DS4 is a 2.1 V / 450 mA high-mu extended-cutoff Nuvistor triode for neutralized grounded-cathode VHF RF amplification in FM and television tuners. Its typical amplification factor is approximately 63–68, transconductance 9–12.5 mA/V, plate resistance 5.44–7 kΩ, and plate current approximately 6.5–7 mA at the published points.

The distinctive extended-cutoff transfer behavior, compact metal-shell construction, low interelectrode capacitances, and dedicated tuner application distinguish the 2DS4 from ordinary general-purpose receiving triodes.