6DS4 — Extended-Cutoff High-Mu Nuvistor VHF RF Triode
An indirectly heated, metal-shell Nuvistor intended for neutralized grounded-cathode VHF amplification and improved weak-signal-area television and FM reception.
Overview
The 6DS4 is a high-mu Nuvistor triode with extended-cutoff characteristics for use as a grounded-cathode, neutralized radio-frequency amplifier in VHF television and FM receiver tuners. RCA's detailed technical sheet explicitly emphasizes improved weak-signal-area reception, distinguishing the 6DS4's intended performance from that of a generic receiving triode.
The tube is intended for color and black-and-white television receivers as well as FM receivers. The related 2DS4 has corresponding signal-electrode characteristics but a different heater supply.
Construction, Basing, and Mechanical Details
The 6DS4 is a single triode containing a control grid, plate, and indirectly heated coated unipotential cathode. Its compact MT4 metal-shell Nuvistor envelope uses a medium ceramic-wafer five-contact base, JEDEC E5-65, with 12AQ basing. It requires a dedicated Nuvistor socket.
The detailed RCA basing drawing assigns pin 2 to the plate, pin 4 to the grid, pin 8 to the cathode, and pins 10 and 12 to the heater. The other indexed positions are marked do not use. The large index lug and shortened pin distinguish the proper socket orientation.
RCA specifies a maximum overall length of 0.800 inch, seated length of 0.625 inch, and diameter of 0.440 inch. The tube can be mounted in any position.
Heater Characteristics
RCA's detailed heater data give 6.3 ± 0.6 V as the stated heater-voltage condition. The 2DS4 uses 2.1 V at 0.45 A and has a published 8-second warm-up time; that warm-up value should not automatically be assigned to the 6DS4, for which the family table leaves the corresponding entry unspecified.
Extended-Cutoff and Weak-Signal Reception
RCA explicitly calls the 6DS4 a high-mu triode having extended-cutoff characteristics and advertises improved weak-signal-area reception.
The characteristic data include low-current grid-bias points of approximately −5 V at 100 µA plate current and −6.8 V at 10 µA plate current. These values illustrate the transfer characteristic toward low plate currents and are specific to the stated test conditions.
The extended-cutoff characteristic is relevant to the receiver front-end role, but the datasheets do not give one universal receiver noise figure or automatic-gain-control transfer law. Actual tuner sensitivity depends on the complete tuned and neutralized circuit.
Typical Electrical Characteristics
These values identify the tube as a high-mu, relatively high-transconductance receiving triode. The characteristic quantities are consistent with the small-signal triode relationship μ ≈ gₘ × rₚ: 0.009 S × 7,000 Ω ≈ 63 and 0.0125 S × 5,440 Ω ≈ 68.
Maximum Ratings and Plate Dissipation
RCA gives 1.5 W maximum plate dissipation with at least 5,000 Ω series plate-circuit resistance; lower resistance requires consultation of the manufacturer's plate-dissipation rating chart. The detailed sheet further explains that a 300 V supply may be used only with appropriate plate resistance and operating conditions to keep actual plate voltage at or below 135 V under maximum-rated dissipation.
Sylvania publishes a 1.0 W plate-dissipation maximum, so the rating differs by manufacturer and conditions. RCA documents metal-shell operating temperature conditions of approximately 125–135°C in its editions.
Interelectrode Capacitances
These capacitances matter in the neutralized VHF amplifier circuit because the grid-to-plate capacitance creates an input-output coupling path. The grouped input and output capacitance definitions include the shell and other named elements.
Plate and Transfer Characteristics
RCA's extended technical sheet includes average plate-current curves, transfer-characteristic curves, and a plate-dissipation-versus-series-resistance rating chart. The curves support interpretation of the tube's extended-cutoff behavior and the dependence of plate current on grid voltage and plate voltage.
The rating chart reinforces the importance of distinguishing the DC supply from the actual voltage at the plate and from the thermal power dissipated within the tube.
Related Designations
The 2DS4 is the 2.1 V / 450 mA heater version of the 6DS4, with the same basic signal-electrode characteristics according to RCA. The DS4 family is distinct from the CW4 high-mu VHF Nuvistor amplifier family in the manufacturer's explicit extended-cutoff designation and characteristic tables.
Technical Summary
The 6DS4 is a 6.3 V / 135 mA high-mu extended-cutoff Nuvistor triode for neutralized grounded-cathode VHF RF amplification in FM and television tuners. Its typical amplification factor is 63–68, transconductance 9–12.5 mA/V, plate resistance 5.44–7 kΩ, and plate current 6.5–7 mA.
Its distinguishing documented application is improved weak-signal-area reception, supported by the extended-cutoff characteristic and detailed RCA receiver-front-end specifications.
