17BQ6GTB — Beam Power Pentode

The 17BQ6GTB is a glass-envelope beam power amplifier designed primarily for service as a horizontal deflection amplifier in television receivers. It is particularly suited for use in both color and black-and-white television designs. Featuring a coated unipotential cathode, the tube is engineered to withstand high-voltage pulses and deliver the high peak currents required by electromagnetic deflection systems.

Construction, Physical Dimensions, and Base Pinout

The 17BQ6GTB is constructed in a T-9 glass bulb envelope equipped with a skirted miniature top cap (such as C1-2, C1-3, or C1-33) and an intermediate or short intermediate shell 7-pin or 8-pin octal base (such as B5-187, B6-81, B6-84, B7-7, or B7-59). The tube can be mounted and operated in any position.

The physical dimensions of the envelope are as follows:

• Maximum diameter: 1.188 inches (1-9/32 inches)
• Maximum seated height: 3.313 inches (3-5/16 inches)
• Maximum overall height: 3.875 inches (3-7/8 inches)

The tube utilizes the 6AM basing diagram, which is viewed from the bottom of the base. Depending on the specific manufacturing variant, pin 1 may be omitted, and the internal electrode connections are distributed as follows:

• Pin 1: No Connection (NC) (may be omitted)
• Pin 2: Heater (H)
• Pin 3: Grid No. 2 (G2) or No Connection (NC)
• Pin 4: Grid No. 1 (G1), Grid No. 2 (G2), or No Connection (NC)
• Pin 5: Grid No. 1 (G1) or No Connection (NC)
• Pin 7: Heater (H)
• Pin 8: Cathode (K) and Grid No. 3 (G3)
• Top Cap: Plate (P)

Heater Characteristics and Warm-up

The heater of the 17BQ6GTB is designed for series-string heater circuits, providing a controlled warm-up characteristic to prevent voltage surges across other tubes in the series chain.

• Heater Voltage (AC or DC): 16.8 V
• Heater Current: 0.45 A (450 mA)
• Heater Warm-up Time: Approximately 11.0 seconds

The heater warm-up time is defined as the time required for the heater voltage to reach 80% of its rated value when four times the rated heater voltage is applied to a series circuit consisting of the heater and a resistance equal to three times the nominal heater operating resistance.

The calculated nominal heater power is 7.56 W, derived from the nominal heater voltage of 16.8 V and heater current of 0.45 A.

Electrical Characteristics and Typical Operation

The 17BQ6GTB operates as a beam power pentode with high transconductance and a low plate knee voltage. Typical operating points and characteristics under Class A1 and zero-bias conditions are detailed below:

* These zero-bias values are measured using a recurrent waveform method to ensure that the maximum ratings of the tube are not exceeded. ** The triode amplification factor (Grid No. 2 to Grid No. 1) is measured under the conditions of $E_b = E_{c2} = 150\text{ V}$ and $E_{[c1](/tubes/C1)} = -22.5\text{ V}$.

Horizontal Deflection Amplifier Ratings

The 17BQ6GTB is rated under the Design Center Rating System for horizontal deflection amplifier service in a 525-line, 30-frame television system. The duty cycle of the voltage pulse must not exceed 15% of the scanning cycle, with a maximum pulse duration of 10 µs.

• Maximum DC Plate Supply Voltage (Boost + DC Power Supply): 600 V
• Maximum Peak Positive Pulse Plate Voltage (Absolute Maximum): 6,000 V
• Maximum Peak Negative Pulse Plate Voltage: 1,250 V
• Maximum DC Grid No. 2 Voltage: 200 V
• Maximum Peak Negative Pulse Grid No. 1 Voltage: 300 V
• Maximum Plate Dissipation: 11 W
• Maximum Grid No. 2 Dissipation: 2.5 W
• Maximum Average Cathode Current: 110 mA
• Maximum Peak Cathode Current: 400 mA
• Maximum Grid No. 1 Circuit Resistance: 0.47 MΩ
• Maximum Bulb Temperature (at hottest point): 220 °C

Heater-Cathode Voltage Ratings

• Heater Negative with respect to Cathode (Total DC and Peak): 200 V max.
• Heater Positive with respect to Cathode (DC): 100 V max.
• Heater Positive with respect to Cathode (Total DC and Peak): 200 V max.

Circuit Protection

When utilizing grid-leak bias, the circuit must incorporate an adequate cathode bias resistor or other protective means to prevent excessive plate and screen dissipation in the event that excitation is lost.

Interelectrode Capacitances and Curve Observations

Direct Interelectrode Capacitances

The approximate direct interelectrode capacitances of the unshielded tube are:

• Grid No. 1 to Plate: 0.6 pF
• Input (Grid No. 1 to Cathode, Heater, Grid No. 2, and Grid No. 3): 15 pF
• Output (Plate to Cathode, Heater, Grid No. 2, and Grid No. 3): 7.0 to 7.5 pF

Qualitative Curve Observations

The electrical characteristics of the 17BQ6GTB are characterized by a sharp knee in the plate current curves, which allows for efficient operation in deflection circuits:

• At $E_{c2} = 100\text{ V}$: The plate current ($I_b$) curves plotted for control grid voltages ($E_{[c1](/tubes/C1)}$) from $0\text{ V}$ to $-25\text{ V}$ show a knee occurring between $50\text{ V}$ and $60\text{ V}$ plate voltage. At $E_{[c1](/tubes/C1)} = 0\text{ V}$, the plate current reaches approximately $170\text{ to }175\text{ mA}$ at a plate voltage of $250\text{ V}$. The screen grid current ($I_{c2}$) peaks at low plate voltages (around $50\text{ mA}$) and drops below $10\text{ mA}$ as the plate voltage rises above $100\text{ V}$.
• At $E_{c2} = 150\text{ V}$: The plate current curves are plotted for $E_{[c1](/tubes/C1)}$ from $0\text{ V}$ to $-40\text{ V}$. At $E_{[c1](/tubes/C1)} = 0\text{ V}$, the knee occurs around $60\text{ V}$ to $75\text{ V}$ plate voltage, with the plate current reaching approximately $280\text{ to }300\text{ mA}$ at $250\text{ V}$ plate voltage. The screen grid current peaks sharply near $25\text{ V}$ plate voltage (reaching up to $100\text{ mA}$ at low plate voltages) and drops below $20\text{ mA}$ at higher plate voltages.

Related Designations

The 17BQ6GTB is identical to the 6BQ6GTB (and the combined 6BQ6GTB/6CU6 designation) except for its heater ratings. The 6BQ6GTB uses a 6.3 V, 1.2 A heater, whereas the 17BQ6GTB is designed with a 16.8 V, 0.45 A heater with a controlled warm-up time for series-string applications.

Technical Summary

The 17BQ6GTB is a glass-envelope, octal-based beam power pentode designed for horizontal deflection amplifier service in television receivers. It features a 16.8 V, 0.45 A heater with a controlled 11-second warm-up time, making it suitable for series-string heater designs. The tube is characterized by high transconductance (5,900 µmhos), a low plate knee voltage, and the ability to withstand peak positive plate pulses up to 6,000 V. With a plate dissipation rating of 11 W and a peak cathode current capability of 400 mA, the 17BQ6GTB provides robust performance in demanding electromagnetic deflection circuits.