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Voltage Pentode - Sharp Cutoff (single) ·Pentode

18GD6

Sharp-cutoff miniature pentode for RF and IF amplification in AC/DC receivers using 100 mA series-heater strings.

Directly heatedCold cathodeCommon cathodeDissimilar
Sections
1
Base
-
Socket code
B7G
Base pins
7
Nominal heater
18 V / 100 mA

Description

18GD6 — Sharp-Cutoff Pentode

The 18GD6 is a miniature, sharp-cutoff pentode featuring a coated unipotential cathode. It is designed primarily for radio frequency (RF) and intermediate frequency (IF) amplifier applications in AC/DC type radio receivers.

Mechanical Design and Pinout

The 18GD6 is constructed in a compact T-5 1/2 glass envelope with a miniature button 7-pin base (designated 7BK). The physical dimensions of the tube are characterized by a maximum diameter of 3/4 inch, a maximum bulb height of 1 7/8 inches, and a maximum overall height of 2 1/8 inches. The tube is designed to operate reliably in any mounting position.

The 7BK base pinout configuration, viewed from the bottom of the tube, is assigned as follows:

Pin NumberElectrode Connection
Pin 1Grid #1 (Control Grid, G1)
Pin 2Cathode (K)
Pin 3Heater (H)
Pin 4Heater (H)
Pin 5Plate (Anode, P)
Pin 6Grid #2 (Screen Grid, G2)
Pin 7Grid #3 (Suppressor Grid, G3) & Internal Shield (I.S.)

Heater Specifications and Design-Maximum Ratings

The 18GD6 is designed for series-string or AC/DC receiver applications, utilizing an 18-volt heater. The electrical ratings and maximum limits are established under the Design-Maximum System.

Heater Ratings

  • Heater Voltage: 18 V
  • Heater Current: 0.10 A (100 mA)
  • Calculated Heater Power: 1.8 W (derived from 18 V multiplied by 0.10 A)

Design-Maximum Limits

  • Maximum Plate Voltage: 150 V
  • Maximum Grid #2 (Screen Grid) Supply Voltage: 150 V
  • Maximum Grid #2 Voltage: Subject to the limits of the manufacturer's rating chart
  • Maximum Plate Dissipation: 2.5 W
  • Maximum Grid #2 Dissipation: 0.6 W
  • Maximum Heater-Cathode Voltage: 100 V

Typical Operating Conditions and Characteristics

In typical Class A1 amplifier service, the suppressor grid (Grid #3) is connected directly to the cathode at the tube socket. Under these conditions, the tube exhibits the following typical operating parameters:

ParameterValue
Heater Voltage18 V
Plate Voltage100 V
Grid #2 Voltage100 V
Grid #3 VoltageConnected to cathode at socket
Cathode Bias Resistor150 \u03a9
Plate Current5 mA
Grid #2 Current2.0 mA
Transconductance4300 \u03bcmhos
Plate Resistance (Approximate)0.5 M\u03a9
Grid #1 Voltage for Plate Current of 10 \u03bca (Approximate)-4.7 V

Direct Interelectrode Capacitances

The high-frequency performance of the 18GD6 is enhanced by its low internal capacitances. The following values are measured with an external shield (specifically shield #316) connected to Pin 7 (Grid #3 and Internal Shield):

  • Grid #1 to Plate (Maximum): 0.0035 \u03bc\u03bcf
  • Input Capacitance [G1 to (H + K + G2 + G3 + I.S.)]: 6.0 \u03bc\u03bcf
  • Output Capacitance [P to (H + K + G2 + G3 + I.S.)]: 5.0 \u03bc\u03bcf

The extremely low grid-to-plate capacitance of 0.0035 \u03bc\u03bcf is a critical parameter for sharp-cutoff pentodes in RF and IF stages, as it minimizes feedback and helps prevent unwanted oscillations in high-gain amplifier circuits.

Socket description

Miniature 7-contact

General specifications

Tube and section characteristics

Properties common to every published source and operating point.

Heater and base

Base
-
Socket code
B7G
Base pins
7
Nominal heater voltage
18 V
Nominal heater current
100 mA
Parallel heater voltage
-
Parallel heater current
-
Series capable
No

Terminal pinout

Electrical assignments shared by every tube using this base designation.

No verified pinout is recorded for this base designation.

Section ratings

1 physical section, each with unique specifications.

Section 1

Pentode

X-ray radiationInterelectrode capacitances
Plate resistance
500000 Ω
Transconductance
0.0043 S
Max plate voltage
150 V
Max plate dissipation
2.5 W
Max screen dissipation
0.6 W

Sharp-cutoff RF/IF pentode; screen voltage governed by rating chart.

Source-dependent data

Operating conditions by source

Each block preserves the test conditions and published values from one reference. Values from different sources are intentionally kept separate.

Data set 01

1961 Tung Sol

Published operating points and test conditions from this source.

SECTION 1

Pentode

Other

  • Plate Voltage

    100 V

Characteristic

  • TransconductancePublished

    4300 uS

Data set 02

1966 Tung Sol Electronic Tubes 3 of 4

Published operating points and test conditions from this source.

SECTION 1

Pentode

Characteristic

  • Grid 1-to-plate capacitance maximum

    0.0035 pF

    WholeTube

  • Input capacitance

    6 pF

    WholeTube

  • Output capacitance

    5 pF

    WholeTube

  • Grid 1 voltage for 10 µA plate current

    -4.7 V

    WholeTube

Other

  • Maximum plate voltage

    150 V

    WholeTube

  • Maximum screen supply voltage

    150 V

    WholeTube

  • Maximum plate dissipation

    2.5 W

    WholeTube

  • Maximum screen dissipation

    0.6 W

    WholeTube

  • Screen voltage

    100 V

    TypicalOperation

  • Cathode bias resistor

    150 ohm

    TypicalOperation

  • Plate current

    5 mA

    TypicalOperation

  • Screen current

    2 mA

    TypicalOperation

  • Transconductance

    4300 µS

    TypicalOperation

  • Plate resistance

    500000 ohm

    TypicalOperation