18016 — Telephone Equipment Pentode

The 18016 is an indirectly heated pentode designed specifically for use in telephone equipment, where it serves as either a pre-amplifier or an output valve. It features a high-voltage heater designed for parallel AC or DC supply, requiring a nominal 21 V. The tube is constructed with a glass envelope and is documented in multiple basing configurations, including versions with a top cap for the control grid ($g_1$) and versions with all connections brought out to a multi-pin base.

Construction and Physical Dimensions

The 18016 is housed in a glass envelope with a maximum diameter of 46 mm and a maximum height of 126 mm (excluding the pins). The base height is specified up to a maximum of 18 mm.

Depending on the physical variant of the 18016, the control grid ($g_1$) is either connected to a top cap on the envelope or brought out directly to one of the base pins. The tube also incorporates an internal shield or metallization ($m$) to minimize interelectrode coupling.

Heater Ratings

The cathode is indirectly heated and can be operated from either an AC or DC supply in a parallel configuration.

• Heater Voltage ($V_f$): 21 V
• Heater Current ($I_f$): 0.335 A
• Calculated Heater Power: $21\text{ V} \times 0.335\text{ A} = 7.035\text{ W}$

Pinout and Basing Configurations

The pin connections for the 18016 vary across different documented configurations.

Top-Cap Configuration A

In this configuration, the control grid ($g_1$) is located on the top cap of the envelope:

• Top Cap: Grid 1 ($g_1$)
• Pin 1: Cathode, Grid 3, and Shield ($k, g_3, s$)
• Pin 2: Heater ($f$)
• Pin 3: Heater ($f$)
• Pin 4: Grid 2 ($g_2$)
• Pin 5: Metal sleeve/shield ($m$)
• Pin 7: Anode ($a$)

Top-Cap Configuration B

An alternative top-cap arrangement assigns the pins as follows:

• Top Cap: Grid 1 ($g_1$)
• Pin 1: Cathode, Grid 3, and Shield ($k, g_3, s$)
• Pin 2: Heater ($f$)
• Pin 3: Heater ($f$)
• Pin 4: Grid 2 ($g_2$)
• Pin 5: No connection
• Pin 6: Metal envelope/shield ($m$)
• Pin 7: Anode ($a$)

Single-Ended Configuration (10-Pin Base)

In this configuration, all electrodes are connected to the base pins, and the control grid is marked with a diamond symbol:

• Pins 2, 3: Heater ($f, f$)
• Pin 4: Grid 2 ($g_2$)
• Pin 5: Metallization/Shield ($m$)
• Pin 6: Anode ($a$)
• Pin 7: Cathode, Grid 3, and Screen ($k, g_3, s$)
• Pin 10: Grid 1 ($g_1$) (marked with a diamond symbol)

Interelectrode Capacitances

The interelectrode capacitances of the 18016 are specified as follows:

• Anode Capacitance ($C_a$): 15 pF
• Grid 1 Capacitance ($C_{g1}$): 14.5 pF
• Anode to Grid 1 Capacitance ($C_{ag1}$): < 0.25 pF
• Grid 1 to Heater Capacitance ($C_{g1f}$): < 0.5 pF

Typical Electrical Characteristics

At a standard operating point, the 18016 exhibits the following typical characteristics:

• Anode Voltage ($V_a$): 125 V
• Grid 2 Voltage ($V_{[g2](/tubes/G2)}$): 125 V
• Cathode Resistor ($R_k$): 115 $\Omega$
• Anode Current ($I_a$): 48 mA
• Grid 2 Current ($I_{[g2](/tubes/G2)}$): 9.5 mA
• Mutual Conductance ($S$): 9 mA/V
• Amplification Factor (Grid 2 to Grid 1) ($\mu_{g2g1}$): 9.5
• Internal Resistance ($R_i$): 16.5 k$\Omega$

Circuit-Specific Operating Conditions

Pre-Amplifier Service

When operated as a pre-amplifier, the 18016 is configured with an anode load resistor ($R_a$) of 3.3 k$\Omega$ under the following conditions:

• Anode Voltage ($V_a$): 125 V
• Grid 2 Voltage ($V_{[g2](/tubes/G2)}$): 125 V
• Cathode Resistor ($R_k$): 115 $\Omega$
• Anode Current ($I_a$): 48 mA
• Grid 2 Current ($I_{[g2](/tubes/G2)}$): 9.5 mA
• Mutual Conductance ($S$): 9 mA/V
• Internal Resistance ($R_i$): 16.5 k$\Omega$
• Voltage Gain ($V_o / V_i$): 3.15 N (Nepers)
• Maximum Grid 1 Resistor ($R_{g1}$):
  • Automatic Bias: 1 M$\Omega$
  • Fixed Grid Bias: 0.5 M$\Omega$

Output Valve Service

When used as an output stage, the tube operates with the same DC bias conditions but is optimized for power delivery into a 3.3 k$\Omega$ load:

• Anode Voltage ($V_a$): 125 V
• Grid 2 Voltage ($V_{[g2](/tubes/G2)}$): 125 V
• Cathode Resistor ($R_k$): 115 $\Omega$
• Anode Current ($I_a$): 48 mA
• Grid 2 Current ($I_{[g2](/tubes/G2)}$): 9.5 mA
• Mutual Conductance ($S$): 9 mA/V
• Internal Resistance ($R_i$): 16.5 k$\Omega$
• Output Power ($W_o$): 0.8 W
• Total Distortion ($d_{tot}$): < 3%
• Maximum Grid 1 Resistor ($R_{g1}$):
  • Automatic Bias: 0.3 M$\Omega$
  • Fixed Grid Bias: 0.15 M$\Omega$

Limiting Values (Absolute Maxima)

The following maximum ratings must not be exceeded under any operating conditions:

• Cold Anode Voltage ($V_{a0}$): Max 300 V
• Anode Voltage ($V_a$): Max 150 V
• Anode Dissipation ($W_a$): Max 5.6 W
• Cold Grid 2 Voltage ($V_{g20}$): Max 300 V
• Grid 2 Voltage ($V_{[g2](/tubes/G2)}$): Max 150 V
• Grid 2 Dissipation ($W_{[g2](/tubes/G2)}$): Max 1.2 W
• Cathode Current ($I_k$): Max 70 mA
• Grid 1 Voltage ($V_{g1}$ at $I_{g1} = +0.3\ \mu\text{A}$): Max -1.3 V
• Heater-to-Cathode Voltage ($V_{fk}$): Max 50 V
• Heater-to-Cathode Resistance ($R_{fk}$): Max 3 k$\Omega$

Technical Summary

The 18016 is a specialized telephone-equipment pentode designed for high-reliability pre-amplifier and output applications. Operating with a 21 V, 0.335 A heater, it provides a mutual conductance of 9 mA/V and an internal resistance of 16.5 k$\Omega$ at a typical anode and screen potential of 125 V. The tube is capable of delivering 0.8 W of output power with less than 3% total distortion when configured as an output valve, or achieving a gain of 3.15 Nepers in pre-amplifier service. Its robust design is reflected in its strict limiting values, including a maximum anode dissipation of 5.6 W and a maximum cathode current of 70 mA.