18013 — Telephone Equipment Pentode

Overview

The 18013 is an indirectly heated pentode designed specifically for use in telephone equipment. It is optimized for high-reliability applications, operating either as a pre-amplifier or as a low-power output valve. The tube features a 4 V heater, a metallized shield connection, and a top-cap control grid configuration to minimize input capacitance and coupling.

Construction, Heater, and Physical Dimensions

The 18013 is constructed with an indirectly heated cathode designed for parallel supply using either AC or DC. The physical envelope is characterized by a maximum bulb diameter of 47 mm and a maximum height of 121 mm (excluding the pins). The base pins have a maximum length of 18 mm.

Heater Ratings

• Heater Voltage ($V_f$): 4 V
• Heater Current ($I_f$): 1.3 A
• Heating Method: Indirect, parallel supply (AC or DC)

Pinout and Connections

The control grid ($g_1$) is brought out to a top cap on the envelope to ensure high isolation. The remaining electrodes are connected to the base contacts as follows:

• Top Cap: Grid 1 ($g_1$)
• Pin 1: Cathode ($k$)
• Pins 2, 3: Heater ($f, f$)
• Pin 4: Grid 3 ($g_3$, suppressor grid)
• Pin 5: Anode ($a$)
• Pin 8: Metallization / Shielding ($m$)
• Pin 10: Grid 2 ($g_2$, screen grid)

Interelectrode Capacitances

The physical layout of the electrodes, including the top-cap control grid and the internal shielding, results in low feedback capacitance:

• Anode capacitance ($C_a$): 7.5 pF
• Grid 1 capacitance ($C_{g1}$): 9.8 pF
• Feedback capacitance ($C_{ag1}$): < 0.012 pF
• Grid 1 to heater capacitance ($C_{g1f}$): < 0.2 pF

Typical Electrical Characteristics

At a standard operating point, the 18013 exhibits high internal resistance and a transconductance of 5 mA/V. The typical characteristics are measured under the following conditions:

Operating Conditions

The 18013 is specified for two distinct operating modes in telephone equipment: as a pre-amplifier and as an output valve.

Pre-amplifier Service

When configured as a pre-amplifier, the tube operates with a 20 k$\Omega$ anode load resistor. Under these conditions, it provides a voltage gain of 4.5 (also expressed as 4.5 N).

• Anode Voltage ($V_a$): 200 V
• Grid 3 Voltage ($V_{g3}$): 0 V
• Grid 2 Voltage ($V_{[g2](/tubes/G2)}$): 200 V
• Cathode Resistor ($R_k$): 265 $\Omega$
• Anode Load Resistor ($R_a$): 20 k$\Omega$
• Anode Current ($I_a$): 8 mA
• Grid 2 Current ($I_{[g2](/tubes/G2)}$): 1.5 mA
• Transconductance ($S$): 5 mA/V
• Internal Resistance ($R_i$): 1 M$\Omega$
• Voltage Gain ($V_o/V_i$): 4.5 (4.5 N)
• Maximum Grid 1 Resistor ($R_{g1}$):
  • With cathode/automatic bias: 1 M$\Omega$
  • With fixed grid bias: 0.5 M$\Omega$

Output Valve Service

When used as an output stage, the anode load resistor is increased to 30 k$\Omega$. This configuration delivers a modest power output with low distortion.

• Anode Voltage ($V_a$): 200 V
• Grid 3 Voltage ($V_{g3}$): 0 V
• Grid 2 Voltage ($V_{[g2](/tubes/G2)}$): 200 V
• Cathode Resistor ($R_k$): 265 $\Omega$
• Anode Load Resistor ($R_a$): 30 k$\Omega$
• Anode Current ($I_a$): 8 mA
• Grid 2 Current ($I_{[g2](/tubes/G2)}$): 1.5 mA
• Transconductance ($S$): 5 mA/V
• Internal Resistance ($R_i$): 1 M$\Omega$
• Output Power ($W_o$): 0.1 W
• Total Distortion ($d_{tot}$): < 5%
• Maximum Grid 1 Resistor ($R_{g1}$):
  • With cathode/automatic bias: 0.3 M$\Omega$
  • With fixed grid bias: 0.15 M$\Omega$

Limiting Values (Absolute Maxima)

To ensure reliable operation in telephone systems, the following maximum ratings must not be exceeded:

Technical Summary

The 18013 is a specialized telephone-grade pentode featuring a 4 V, 1.3 A heater, a top-cap control grid, and an integrated metallized shield. It is characterized by a high internal resistance of 1 M$\Omega$ and a transconductance of 5 mA/V under typical operating conditions. Designed for dual-role service, it functions effectively as a pre-amplifier (yielding a gain of 4.5 N with a 20 k$\Omega$ load) or as a low-power output valve (delivering 0.1 W into a 30 k$\Omega$ load with less than 5% total distortion). Strict limiting values, including a maximum anode dissipation of 1.8 W and a maximum cathode current of 12 mA, ensure long-term stability in demanding telecommunication circuits.