17LD8 — Triode-Pentode Vacuum Tube

The 17LD8 is a multi-section vacuum tube containing a triode and a pentode section within a single envelope. It is designed for series heater operation and is primarily intended for combined functions as a vertical deflection oscillator and amplifier.

Mechanical Specifications and Pinout

The 17LD8 is constructed in a T-9 glass bulb with an E9-75 9-pin base. It features coated unipotential cathodes and can be mounted in any position. The tube utilizes the 9QT basing arrangement, which provides the following pin connections:

Heater Characteristics and Ratings

The heater is designed for series-string operation with a controlled warm-up time. The heater specifications and design-maximum limits are detailed below:

• Nominal Heater Voltage: 16.8 V
• Average Heater Current: 450 mA
• Heater Warm-up Time: 11 Seconds
• Heater Current Limits: 420 mA minimum to 480 mA maximum

Heater-Cathode Voltage Limits

• Heater Negative with Respect to Cathode (Total DC and Peak): 200 Volts maximum
• Heater Positive with Respect to Cathode (DC): 100 Volts maximum
• Heater Positive with Respect to Cathode (Total DC and Peak): 200 Volts maximum

Average Electrical Characteristics

The 17LD8 contains two distinct electrical sections with the following typical characteristics:

Triode Section

• Plate Voltage: 150 Volts
• Grid No. 1 Voltage: -5 Volts
• Plate Current: 3.3 mA
• Transconductance: 1,900 µmhos
• Amplification Factor: 21.5
• Plate Resistance (approx.): 11,300 Ohms
• Grid Voltage for Ib = 10 µA (approx.): -10 Volts

Pentode Section

• Plate Voltage: 120 Volts
• Grid No. 2 Voltage: 110 Volts
• Grid No. 1 Voltage: -8 Volts
• Plate Current: 46 mA
• Grid No. 2 Current: 4 mA
• Transconductance: 7,100 µmhos
• Plate Resistance (approx.): 11,700 Ohms
• Grid Voltage for Ib = 100 µA (approx.): -25 Volts

Instantaneous Plate Knee Values

At a plate voltage of 45 V, grid No. 2 voltage of 110 V, and grid voltage of 0 V, the instantaneous knee values are:

• Plate Current (Ib): 122 mA
• Grid No. 2 Current (Ic2): 17 mA

Design-Maximum Ratings and Application Guidelines

The 17LD8 is rated under the design-maximum system for vertical deflection service. When operating in stages that utilize grid leak bias, designers must provide an adequate bias resistor or other suitable protective means to safeguard the tube in the event that excitation is lost.

Triode Section (Vertical Oscillator Service)

• Plate Voltage: 250 Volts maximum
• Peak Negative Grid No. 1 Voltage: 400 Volts maximum
• Plate Dissipation: 1.0 Watts maximum
• Average Cathode Current: 20 mA maximum
• Peak Cathode Current: 70 mA maximum
• Grid Circuit Resistance (Self Bias): 2.2 Megohms maximum
• Grid Circuit Resistance (Fixed Bias): 1.0 Megohm maximum

Pentode Section (Vertical Amplifier Service)

• Plate Voltage: 250 Volts maximum
• Grid No. 2 Voltage: 200 Volts maximum
• Peak Positive Pulse Plate Voltage: 2,000 Volts maximum (The duty cycle of this voltage pulse must not exceed 15% of one scanning cycle in a standard 525-line, 30-frame television system)
• Peak Negative Grid No. 1 Voltage: 150 Volts maximum
• Plate Dissipation: 7 Watts maximum
• Grid No. 2 Dissipation: 1.8 Watts maximum
• Average Cathode Current: 70 mA maximum
• Peak Cathode Current: 245 mA maximum
• Grid Circuit Resistance (Self Bias): 2.2 Megohms maximum
• Grid Circuit Resistance (Fixed Bias): 1.0 Megohm maximum

Direct Interelectrode Capacitances

The direct interelectrode capacitances are measured without an external shield:

Triode Section

• Grid to Plate: 3.8 pF
• Input (g to h + Tk): 2.0 pF
• Output (p to h + Tk): 0.4 pF

Pentode Section

• Grid No. 1 to Plate: 0.26 pF maximum
• Input (g1 to h + Pk, g3): 13 pF
• Output (p to h + Pk, g3): 7 pF