17GV5 — Beam Power Pentode

An indirectly heated Compactron beam power tube designed for horizontal-deflection amplifier service in television receivers.

Overview

The 17GV5 is a high-performance beam power pentode constructed in a Compactron (or duodecar) envelope. It is designed primarily for use as a horizontal-deflection amplifier in television receivers operating under 525-line, 30-frame scanning systems. The 17GV5 is electrically identical to the 6GV5 except for its heater ratings, which are tailored for series-string heater circuits.

The tube features high peak plate current capabilities at low plate voltages, a characteristic essential for efficient horizontal-deflection service. It is designed to withstand high-voltage pulses on the plate and contains internal beam-confining electrodes (Grid No. 3) connected internally to the cathode.

Mechanical Construction and Physical Dimensions

The 17GV5 is housed in a T-12 glass bulb with a 12-pin button base (E12-74) conforming to the JEDEC 12-79 outline. The plate connection is made via a miniature top cap (C1-3) to isolate the high-voltage pulse from the base pins, although some documentation also associates the plate with a base pin. The tube can be mounted in any position.

The physical dimensions of the envelope are as follows:

• Maximum Diameter: 1.563 inches
• Maximum Seated Height: 3.250 inches
• Maximum Overall Height: 3.625 inches

Basing and Pin Configuration

The 17GV5 utilizes a 12-pin button base requiring a duodecar 12-contact socket. While the basing arrangement is designated as 12DR, different technical specifications record varying pin assignments for this configuration. The variations in published pinout descriptions are summarized below:

These variations highlight the importance of verifying the specific socket wiring against the physical tube structure in practical applications.

Heater Ratings and Characteristics

The 17GV5 incorporates a coated unipotential cathode. The heater is designed for series-string operation with a controlled warm-up time to ensure reliable performance in series-connected heater chains.

• Heater Voltage (Average): 16.8 V (AC or DC)
• Heater Current (Average): 0.45 A (450 mA)
• Heater Supply Limits (Current Operation): 450 ± 30 mA
• Heater Warm-up Time (Average): 11 seconds
  (Defined as the time required to reach 80% of the rated heater voltage when four times the rated voltage is applied in series with three times the nominal heater resistance.)

Heater-Cathode Voltage Limits

To prevent insulation breakdown between the heater and cathode, the following design-maximum voltage limits must be observed:

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

Direct Interelectrode Capacitances

The approximate direct interelectrode capacitances of the 17GV5, measured without an external shield, are:

• Grid No. 1 to Plate ($G_1$ to $P$): 0.6 pF
• Input ($G_1$ to $H + K + G_2 + \text{Beam Plates}$): 16 pF
• Output ($P$ to $H + K + G_2 + \text{Beam Plates}$): 7.0 pF

Electrical Characteristics and Operating Points

The electrical characteristics of the 17GV5 are documented under three distinct pentode operating conditions, as well as a triode-connected configuration.

Pentode Connection Characteristics

• Condition A (High-Voltage Cutoff):

  • Plate Voltage: 5000 V
  • Grid No. 2 Voltage: 150 V
  • Grid No. 1 Voltage (Approximate for $I_b = 1.0\text{ mA}$): $-100\text{ V}$

• Condition B (Peak Current / Knee):

  • Plate Voltage: 60 V
  • Grid No. 2 Voltage: 150 V
  • Grid No. 1 Voltage: 0 V
  • Plate Current ($I_b$): 345 mA (measured via a recurrent waveform applied for a maximum duration of 2 seconds to prevent thermal damage)
  • Grid No. 2 Current ($I_{c2}$): 27 mA (measured via recurrent waveform)

• Condition C (Class A / Normal Operation):

  • Plate Voltage: 250 V
  • Grid No. 2 Voltage: 150 V
  • Grid No. 1 Voltage: $-22.5\text{ V}$
  • Plate Current ($I_b$): 65 mA
  • Grid No. 2 Current ($I_{c2}$): 1.8 mA
  • Transconductance ($g_m$): 7300 µmhos
  • Plate Resistance ($r_p$, Approx.): 18,000 Ω
  • Grid No. 1 Voltage (Approximate for $I_b = 1.0\text{ mA}$): $-42\text{ V}$

Triode Connection Characteristics

When the screen grid (Grid No. 2) is tied directly to the plate, the 17GV5 operates as a low-mu triode under the following conditions:

• Plate Voltage: 150 V
• Grid No. 2 Voltage: 150 V
• Grid No. 1 Voltage: $-22.5\text{ V}$
• Amplification Factor ($\mu$): 4.4

Horizontal-Deflection Service Ratings

The 17GV5 is rated under the Design-Maximum System (EIA Standard RS-239) for horizontal-deflection amplifier service in television receivers. These ratings represent the absolute limits within which the tube must be operated to ensure reliable service life.

Circuit-Specific Operating and Protection Notes

In horizontal-deflection circuits, the control grid (Grid No. 1) often operates with grid-leak bias. Because grid-leak bias depends entirely on the presence of an active drive signal (excitation), any failure in the oscillator or drive stage will cause the bias to collapse to zero.

To prevent catastrophic thermal runaway and destruction of the tube under such conditions, the 17GV5 requires a protective cathode-bias resistor or other suitable automatic protection means to limit the plate and screen currents in the absence of excitation.

Technical Summary

The 17GV5 is a robust Compactron beam power pentode designed specifically for the demanding role of a horizontal-deflection amplifier in television receivers. It features a 16.8 V, 450 mA heater with a controlled 11-second warm-up time, making it ideal for series-string heater configurations.

Electrically, the tube is capable of delivering high peak currents (up to 345 mA plate current at a plate voltage of only 60 V) and is rated to withstand peak positive plate pulses of up to 6500 V. With a plate dissipation rating of 17.5 W and a transconductance of 7300 µmhos under typical Class A conditions, the 17GV5 provides the high power handling and efficiency required for electromagnetic deflection systems. Proper circuit design must incorporate protective biasing measures to safeguard the tube against excitation loss.