19DK3 — Half-Wave Vacuum Rectifier and Damper Diode

The 19DK3 is a heater-cathode type half-wave vacuum rectifier designed specifically for use as a damping diode in the horizontal-deflection circuits of television receivers, including color television receivers. It features a specialized heater-cathode insulating system that enables high peak voltage ratings, making it suitable for the demanding electrical stresses of television horizontal-deflection systems. The tube is constructed in a T-9 glass envelope with a 9-pin novar base and operates with a nominal 19-volt heater.

Mechanical Construction and Physical Dimensions

The 19DK3 is housed in a T-9 glass envelope and utilizes a button 9-pin novar base (E9-89) with a 0.687-inch pin circle, requiring a standard novar 9-contact socket. The tube can be operated in any mounting position.

The physical dimensions of the envelope are:

• Maximum overall length: 3.880 inches
• Maximum seated height: 3.500 inches
• Minimum seated height: 3.250 inches
• Maximum diameter: 1.188 inches
• Minimum diameter: 1.062 inches

Depending on the manufacturer's specification, the tube may feature a top cap (EIA C1-2, skirted miniature) connected to the cathode to isolate the high-voltage terminal from the base pins. The outline drawing is classified under EIA 9-117 or outlines section 35A.

Heater Characteristics

The 19DK3 is designed for series heater strings or dedicated power supplies, featuring a controlled warm-up time.

The average heater warm-up time of 11 seconds is measured in series with a resistance equal to three times the bogey voltage divided by the bogey current, with four times the bogey voltage applied.

Terminal Connections and Basing Variations

The 19DK3 uses the EIA 9SG basing diagram, but documentation describes two distinct terminal configurations.

Configuration A (All-Base Connections)

In this configuration, all active electrodes are connected directly to the 9-pin base:

• Pin 1: Internal Connection (IC) — Do not use as a tie point
• Pin 2: Cathode (K)
• Pin 3: Internal Connection (IC) — Do not use as a tie point
• Pin 4: Heater (H)
• Pin 5: Heater (H)
• Pin 6: Internal Connection (IC) — Do not use as a tie point
• Pin 7: Plate (P)
• Pin 8: Internal Connection (IC) — Do not use as a tie point
• Pin 9: No Connection (NC) — Do not use as a tie point

Under this specification, socket terminals 1, 3, 6, 8, and 9 must not be used as tie points.

Configuration B (Top-Cap Cathode Connection)

In this configuration, the cathode is routed to a top cap to maximize high-voltage isolation, and the plate is connected to multiple base pins:

• Pin 1: Heater Insulation Coil (may be used as a tie point for components at or near heater potential)
• Pin 2: Plate (P)
• Pin 3: No Connection (NC)
• Pin 4: Heater (H)
• Pin 5: Heater (H)
• Pin 6: Internal Connection (IC) — Do not use
• Pin 7: Plate (P)
• Pin 8: Internal Connection (IC) — Do not use
• Pin 9: No Connection (NC)
• Top Cap (C1-2): Cathode (K)

Direct Interelectrode Capacitances

Measured without an external shield, the approximate direct interelectrode capacitances of the 19DK3 are:

• Cathode to Plate and Heater ($k$ to $[p + h]$): 22.0 pF
• Plate to Cathode and Heater ($p$ to $[k + h]$): 13.6 pF
• Heater to Cathode ($h$ to $k$): 1.1 pF (or 1.10 pF)

Damper Service Ratings

The 19DK3 is rated under the Design-Maximum system for operation in television receivers (specifically 525-line, 30-frame systems). The voltage pulse duty cycle must not exceed 15% of one horizontal scanning cycle.

Heater-Cathode Voltage Ratings

The unique heater-cathode insulation system allows high voltage differentials between the heater and cathode:

• Heater Positive with Respect to Cathode:
  • DC Component: 100 V
  • Total DC and Peak: 300 V
• Heater Negative with Respect to Cathode:
  • DC Component: 900 V
  • Total DC and Peak: 6,500 V

Electrical Characteristics and Plate Curves

The tube exhibits a low internal voltage drop during conduction, which is critical for high-efficiency damper service.

• Tube Voltage Drop:
  • 16 V at a plate current ($I_b$) of 400 mA
  • 25 V at a plate current ($I_b$) of 800 mA

Qualitative Curve Analysis

At the rated heater voltage, the average plate characteristics show that the plate current rises non-linearly from 0 V to approximately 5 V. Beyond 5 V, the characteristic becomes highly linear. The relationship between plate voltage and instantaneous plate current is illustrated by the following points:

• At 16 V plate potential, plate current reaches 500 mA.
• At 28 V plate potential, plate current reaches 1000 mA.
• At 39 V plate potential, plate current reaches 1500 mA.
• At 48 V plate potential, plate current reaches 2000 mA.

Technical Summary

The 19DK3 is a specialized novar-based half-wave vacuum rectifier designed for television damper service. Operating with a 19 V, 0.6 A heater, it features a robust heater-cathode insulation system capable of withstanding peak negative heater-to-cathode voltages up to 6,500 V. With a maximum plate dissipation of 9.0 W, a peak plate current rating of 1,200 mA, and a low voltage drop of 25 V at 800 mA, the 19DK3 provides efficient energy recovery and damping in horizontal-deflection circuits.