16GK6 — Power Pentode

The 16GK6 is a miniature, high-transconductance power pentode (also characterized as a beam power pentode) designed for use in the output stages of high-quality audio amplifiers and the video output stages of both color and black-and-white television receivers. It features a coated unipotential cathode and is specifically engineered for series heater string operation in television and audio equipment.

The 16GK6 is electrically identical to the 6GK6 and 10GK6 vacuum tubes, differing only in its heater voltage and current ratings. This shared design allows the 16GK6 to deliver high power output with low distortion while operating under standard pentode or push-pull configurations.

Construction, Physical Specifications, and Basing

The 16GK6 is constructed in a T-6 1/2 glass envelope with a miniature 9-pin button base (designated JEDEC E9-1). The tube is designed to operate in any mounting position, providing flexibility in chassis layout.

Physical Dimensions

• Maximum Diameter: 0.875 inches
• Maximum Seated Height: 2.812 inches
• Maximum Overall Height: 3.062 inches

Pinout and Basing Diagram (9GK)

The tube utilizes the 9GK basing arrangement. When viewed from the bottom of the tube, the pin connections are assigned as follows:

The internal connection of Grid No. 3 to the internal shield, accessible via both Pin 1 and Pin 9, assists in minimizing stray capacitances and shielding the sensitive control grid from the plate.

Heater Characteristics and Ratings

The 16GK6 is designed for series heater string operation, requiring a controlled current to ensure reliable operation when wired in series with other tubes.

The average heater warm-up time of 11 seconds is specifically defined under controlled conditions: it represents the time required for the voltage across the heater to reach 80% of its rated voltage after applying four times the rated heater voltage to a circuit consisting of the tube heater in series with an external resistance equal to three times the nominal heater operating resistance. This controlled warm-up characteristic prevents voltage surges across individual heaters in series-string television receivers during start-up.

Direct Interelectrode Capacitances

The 16GK6 exhibits low interelectrode capacitances, which is beneficial for maintaining high-frequency performance in video output stages:

• Grid No. 1 to Plate (Maximum): 0.14 pF
• Input (G1 to Cathode, Heater, G2, G3, and Internal Shield): 10 pF
• Output (Plate to Cathode, Heater, G2, G3, and Internal Shield): 7 pF

Maximum Ratings (Design-Maximum Values)

The maximum ratings of the 16GK6 must be strictly observed to prevent premature failure or degradation of the tube. These values are established under the Design-Maximum Rating System:

Vibrator Power Supply Derating

When the heater and positive voltages for the 16GK6 are obtained from a storage battery by means of a vibrator power supply, the maximum allowable ratings must be derated to protect the tube from voltage spikes and fluctuations. Under these specific conditions:

• Maximum Plate Voltage: 275 V
• Maximum Grid No. 2 Voltage: 275 V
• Maximum Plate Dissipation: 9.9 W

Maximum Circuit Values

• Grid No. 1 Circuit Resistance (Fixed-Bias Operation): 0.3 Megohm max
• Grid No. 1 Circuit Resistance (Cathode-Bias/Self-Bias Operation): 1.0 Megohm max

Typical Operating Conditions and Characteristics

The 16GK6 can be operated as a single-ended Class A1 amplifier, or in push-pull configurations under Class AB1 or Class B operation.

Class A1 Amplifier (Single Tube)

At a typical operating point, a single 16GK6 provides a power output of 5.7 Watts with 10% total harmonic distortion:

Push-Pull Class AB1 and Class B Amplifiers (Two Tubes)

For higher power output and lower distortion, two 16GK6 tubes can be operated in push-pull. The following table outlines typical operating parameters for both Class AB1 and Class B push-pull configurations:

Analysis of Characteristic Curves

The average plate characteristics of the 16GK6 demonstrate its high efficiency and high transconductance. When plate current ($I_b$) and screen current ($I_{c2}$) are plotted against plate voltage at a fixed screen voltage ($E_{c2} = 250$ V), several key behaviors are evident:

1. Sharp Pentode Knee: The plate current rises rapidly at very low plate voltages (below 50 V) before transitioning into a nearly flat, horizontal region. This sharp knee allows for a wide output voltage swing without entering the highly non-linear region of operation, which is critical for maximizing power output and minimizing distortion in audio and video applications.
2. Screen Current Behavior: The screen-grid current ($I_{c2}$) is highest when the plate voltage is near zero, as the screen grid intercepts a larger portion of the electron stream. As the plate voltage increases past the knee, the screen current drops significantly and stabilizes at a low value (typically 5.5 mA under zero-signal conditions), reducing screen dissipation and improving overall efficiency.
3. Grid Bias Spacing: The curves for different control-grid voltages ($E_{[c1](/tubes/C1)}$ from 0 V to -10 V) are evenly spaced, indicating a highly linear transfer characteristic over a wide operating range. This linearity is reflected in the low total harmonic distortion (3% to 4%) achieved in push-pull configurations.

Technical Summary

The 16GK6 is a high-performance, miniature power pentode featuring a 16.0 V, 0.3 A heater with a controlled 11-second warm-up time, making it ideal for series heater string applications. Utilizing a 9-pin miniature button base (E9-1) with a 9GK basing diagram, it provides separate connections for all electrodes, including dual pins for the suppressor grid and internal shield to optimize high-frequency stability.

With a high transconductance of 11,300 µmhos and a plate dissipation rating of 13.2 Watts, the 16GK6 is capable of delivering 5.7 Watts of audio power in single-ended Class A1 service, and up to 17 Watts in push-pull Class AB1 or Class B configurations. Its excellent linearity, low interelectrode capacitances, and robust design-maximum ratings make it an exceptionally versatile tube for both high-fidelity audio output stages and television video amplifiers.