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Voltage - Triode (with diode, heptode or hexode) ·Heptode-Triode

19D8

Triode-heptode frequency changer for radio receivers, combining a dedicated oscillator triode with a heptode mixer. Manufacturer literature also permits the heptode to serve independently as an RF or IF amplifier.

Directly heatedCold cathodeCommon cathodeDissimilar
Sections
2
Base
-
Socket code
B9A
Base pins
9
Nominal heater
19 V / 100 mA

Description

19D8 — Triode Heptode Vacuum Tube

An indirectly heated triode heptode designed primarily for frequency changer applications, where the heptode section can also serve as an RF or IF amplifier.

Overview

The 19D8 (also designated as the UCH81) is an indirectly heated triode heptode vacuum tube. It is housed in a glass envelope with a B9A-Noval base and is designed to operate in any mounting position. The tube is primarily utilized as a frequency changer in radio receivers, with the heptode section capable of functioning as a radio-frequency (RF) or intermediate-frequency (IF) amplifier, and the triode section operating as an RF oscillator.

Physical Dimensions and Base Connections

The 19D8 features a compact physical construction with the following maximum dimensions:

  • Maximum overall length: 67.5 mm
  • Maximum seated height: 60.5 mm
  • Maximum bulb diameter: 22.2 mm

The tube utilizes a standard B9A-Noval nine-pin base. The pinout configuration is assigned as follows:

PinConnection
1Screen grids g2 and g4 (Heptode)
2Control grid g1 (Heptode)
3Cathode, suppressor grid g5, and internal shield
4Heater
5Heater
6Anode (Heptode)
7Mixer grid g3 (Heptode)
8Anode (Triode)
9Grid (Triode)

Heater and Heater-Cathode Ratings

The heater is designed for series or parallel AC or DC operation, making it suitable for a variety of receiver power supply configurations.

ParameterValue
Nominal heater voltage19.0 V
Nominal heater current0.1 A
Maximum heater-to-cathode voltage100 V
Maximum heater-to-cathode circuit resistance20 kΩ

Electrical Characteristics and Maximum Ratings

The 19D8 has separate maximum ratings and electrical characteristics defined for its heptode and triode sections. These limits must be observed to ensure reliable operation.

Heptode Section Ratings

  • Maximum supply voltage: 550 V
  • Maximum anode voltage: 250 V
  • Maximum screen grid voltage (Vg2,g4): 125 V (increases to 200 V if anode current Ia is less than 1 mA)
  • Maximum anode dissipation: 1.7 W
  • Maximum screen grid dissipation: 1.0 W
  • Maximum cathode current: 12.5 mA
  • Maximum control grid voltage (Vg1 at Ig1 = +0.3 µA): -1.3 V
  • Maximum mixer grid voltage (Vg3 at Ig3 = +0.3 µA): -1.3 V
  • Maximum control grid-to-cathode resistance (Rg1-k): 3.0 MΩ
  • Maximum mixer grid-to-cathode resistance (Rg3-k): 3.0 MΩ (reduced to 20 kΩ if switched without a direct connection between g3 and the triode grid gt)

Triode Section Ratings and Characteristics

  • Maximum anode voltage: 250 V
  • Maximum anode dissipation: 0.8 W
  • Maximum mean cathode current: 6.5 mA
  • Maximum grid voltage (Ig = +0.3 µA): -1.3 V
  • Maximum grid-to-cathode resistance (Rg-k): 3.0 MΩ

Under static Class A conditions (Va = 100 V, Vg = 0 V), the triode section exhibits the following typical characteristics:

  • Anode current (Ia): 13.5 mA
  • Amplification factor (µ): 22
  • Transconductance (gm): 3.7 mA/V

Typical Operating Conditions

The 19D8 can be configured in several standard operating modes depending on the receiver design requirements.

Heptode Section as an AM Frequency Changer

In this mode, the heptode section acts as a mixer. Typical operating parameters are specified for three supply voltages:

ParameterCondition ACondition BCondition C
Anode and supply voltage (Va = Vb)100 V170 V200 V
Screen grid resistor (Rg2g4)10 kΩ10 kΩ10 kΩ
Grid resistor (Rg3gt)47 kΩ47 kΩ47 kΩ
Grid current (Ig3gt)115 µA200 µA230 µA
Control grid voltage (Vg1)-1.2 V-2.2 V-2.6 V
Cathode resistor (Rk)150 Ω150 Ω150 Ω
Anode current (Ia)1.7 mA3.2 mA3.7 mA
Screen grid current (Ig2g4)3.7 mA6.8 mA8.1 mA
Conversion conductance (gc)620 µA/V750 µA/V775 µA/V
Anode resistance (ra)0.8 MΩ0.9 MΩ1.0 MΩ
Equivalent noise resistance (Req)62 kΩ70 kΩ75 kΩ
Grid voltage for 100:1 gc reduction-14.5 V-24 V-28 V

Heptode Section as an IF or RF Amplifier

When used as a straight amplifier, the mixer grid (g3) is held at 0 V.

ParameterCondition ACondition BCondition C
Anode and supply voltage (Va = Vb)100 V170 V200 V
Screen grid resistor (Rg2g4)18 kΩ18 kΩ18 kΩ
Screen grid voltage (Vg2g4)60 V100 V125 V
Mixer grid voltage (g3)0 V0 V0 V
Control grid voltage (Vg1)-1.2 V-2.2 V-2.6 V
Anode current (Ia)3.4 mA6.2 mA7.6 mA
Screen grid current (Ig2g4)2.2 mA3.8 mA4.3 mA
Transconductance (gm)2.0 mA/V2.3 mA/V2.4 mA/V
Anode resistance (ra)0.5 MΩ0.6 MΩ0.6 MΩ
Inner amplification factor (g1 to g2,g4)202020
Equivalent noise resistance (Req)5.8 kΩ8.8 kΩ9.7 kΩ
Grid voltage for 100:1 gm reduction-16.5 V-28 V-33 V

Triode Section as an RF Oscillator

When operating as the local oscillator in a frequency changer circuit, the triode section is typically configured with the following parameters:

ParameterCondition ACondition BCondition C
Supply voltage (Vb)100 V170 V200 V
Anode resistor (Rat)15 kΩ15 kΩ15 kΩ
Grid resistor (Rgt)47 kΩ47 kΩ47 kΩ
Grid current (Igt)120 µA200 µA240 µA
Anode current (Iat)2.5 mA4.5 mA5.4 mA
Effective transconductance (gm(eff))530 µA/V580 µA/V580 µA/V

Interelectrode and Inter-Section Capacitances

The internal capacitances of the 19D8 are critical for high-frequency performance and stability. The values are categorized by section and the coupling between sections.

Triode Section Capacitances

  • Input capacitance (Cin): 2.6 pF
  • Output capacitance (Cout): 2.2 pF
  • Grid-to-anode capacitance (Ca-g): 1.0 pF
  • Grid-to-heater capacitance (Cg-h): < 0.02 pF

Heptode Section Capacitances

  • Input capacitance, grid 1 (Cin(g1)): 4.8 pF
  • Input capacitance, grid 3 (Cin(g3)): 6.0 pF
  • Output capacitance (Cout): 7.9 pF
  • Anode-to-grid 1 capacitance (Ca-g1): < 0.01 pF
  • Grid 1-to-heater capacitance (Cg1-h): < 0.02 pF
  • Grid 1-to-grid 3 capacitance (Cg1-g3): < 0.3 pF
  • Grid 3-to-heater capacitance (Cg3-h): < 0.06 pF

Inter-Section Capacitances

  • Heptode anode to triode anode (Cah-at): 0.20 pF
  • Heptode anode to triode grid (Cah-gt): < 0.09 pF
  • Heptode anode to combined grid 3 and triode grid (Cah-g3gt): < 0.35 pF
  • Heptode grid 1 to triode grid (Cg1-gt): < 0.06 pF
  • Heptode grid 1 to combined triode grid and grid 3 (Cg1-gt,g3): < 0.17 pF
  • Heptode grid 1 to combined grid 3 and triode grid (Cg1-g3,gt): < 0.45 pF

Microphony and Operating Considerations

The 19D8 does not require special structural or mounting precautions against microphony under standard operating conditions, provided that the audio output power of the receiver is 50 mW or less, and the input signal voltage is at least 50 mV for the heptode section or at least 25 mV for the triode section.

Characteristic Curves and Design Interpretation

The performance of the 19D8 under dynamic conditions is illustrated by its characteristic relationships:

  • Heptode Characteristics vs. Oscillator Grid Current: At fixed operating potentials (Va = Vb = 200 V, Rg2g4 = 10 kΩ, Rgtg3 = 47 kΩ, and Vg1 = -2.6 V), parameters such as anode current (Ia), screen grid current (Ig2g4), conversion conductance (gc), anode resistance (ra), and oscillator voltage (Vosc) vary systematically as the oscillator grid current is swept from 0 to 500 µA.
  • Conversion Conductance vs. Control Grid Voltage (Vg1): The conversion conductance (gc) is highly dependent on the control grid bias. At supply voltages of 170 V and 200 V, the relationship is plotted across various screen grid voltages (Vg2g4 = 50, 100, 150, and 200 V), demonstrating the automatic volume control (AVC) or automatic gain control (AGC) capability of the heptode section.

Technical Summary

The 19D8 is a versatile, indirectly heated triode heptode designed for frequency changer and RF/IF amplification duties. Operating with a 19.0 V, 0.1 A heater, it integrates a high-performance heptode section and a triode section within a single B9A-Noval envelope. The heptode section provides excellent conversion and amplification characteristics with robust AGC capabilities, while the triode section serves as an efficient local oscillator. With low inter-section capacitances and minimal microphonic sensitivity under standard operating conditions, the 19D8 is a highly integrated solution for compact receiver designs.

Socket description

Small-button Noval 9-contact

General specifications

Tube and section characteristics

Properties common to every published source and operating point.

Heater and base

Base
-
Socket code
B9A
Base pins
9
Nominal heater voltage
19 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

2 physical sections, each with unique specifications.

Section 1

Triode

X-ray radiationInterelectrode capacitances
Plate resistance
19000 Ω
Transconductance
0.004 S
Amplification factor
22
Max plate voltage
250 V
Max plate dissipation
1.5 W
Max cathode current
15 mA

Published ratings and characteristics promoted from the approved German source.

Section 2

Heptode

X-ray radiationInterelectrode capacitances
Plate resistance
1000000 Ω
Transconductance
0.000775 S
Max plate voltage
250 V
Max screen voltage
250 V
Max plate dissipation
1.5 W
Max screen dissipation
1 W
Max cathode current
25 mA

Published ratings and characteristics promoted from the approved German source.

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

1953 RFT Rundfunk Technik

Published operating points and test conditions from this source.

SECTION 1

Triode

Other

  • HeaterVoltageNominal

    6.3 V

    Nominal

  • HeaterCurrentNominal

    300 mA

    Nominal

  • Maximum Plate Voltage

    250 V

  • Maximum Plate Dissipation

    1.5 W

  • Maximum Cathode Current

    15 mA

Characteristic

  • Transconductance

    3800 µS

    Typical

  • Amplification Factor

    22

    Typical

  • Plate Resistance

    19000 ohm

    Typical

SECTION 2

Heptode

Other

  • HeaterVoltageNominal

    6.3 V

    Nominal

  • HeaterCurrentNominal

    300 mA

    Nominal

  • Maximum Plate Voltage

    300 V

  • Maximum Screen Voltage

    250 V

  • Maximum Plate Dissipation

    1.5 W

  • Maximum Screen Dissipation

    1 W

  • Maximum Cathode Current

    25 mA

Characteristic

  • Transconductance

    775 µS

    Typical

  • Plate Resistance

    1000000 ohm

    Typical

Data set 02

1961 Ferranti Technical Handbook

Published operating points and test conditions from this source.

SECTION 1

Triode

Application

  • Application

    Oscillator

SECTION 2

Heptode

Application

  • Application

    Frequency changer / RF-IF amplifier