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Specialized - Switching Tube ·Thyratron

1267

Mullard 1267 cold-cathode gas-filled triggered switching triode with starter electrode, 225 V maximum operating anode voltage and 25 mA maximum continuous cathode current.

Directly heatedCold cathodeCommon cathodeDissimilarSpecialized
Sections
1
Base
-
Socket code
IO
Base pins
8
Nominal heater
-

Description

1267 — Cold-Cathode Gas-Filled Triode

The 1267 is a cold-cathode gas-filled triode designed for switching and control applications. As a cold-cathode device, it operates without a heater filament, eliminating the need for a heater power supply and avoiding any warm-up delay. The tube is classified under gas-filled triodes and tetrodes in the Mullard preferred types range.

Physical Construction and Base Connections

The 1267 is constructed with a glass envelope and is fitted with a standard octal base. The physical dimensions of the tube are specified as follows:

  • Maximum Overall Length (L): 100 mm
  • Maximum Diameter (D): 31 mm

The electrical connections for the active elements are routed to specific pins on the octal base:

  • Cathode: Connected to Pin 2
  • Anode: Connected to Pin 5
  • Grid (Starter Anode): Connected to Pin 7

Electrical Characteristics and Operating Limits

The operation of the 1267 is defined by specific ionization thresholds, conduction voltage drops, and current handling capabilities.

Voltage and Triggering Thresholds

  • Maximum Operating Anode Voltage: When the starter anode (grid) is connected directly to the cathode, the maximum operating anode voltage is 225 V. This represents the upper limit of anode voltage that can be applied without causing self-ionization in the absence of a trigger signal.
  • Starter Anode-Cathode Breakdown Voltage: The voltage required to initiate ionization between the starter anode and the cathode is between a minimum of 70 V and a maximum of 90 V.
  • Starter Anode Current for Anode Breakdown: To trigger the main anode-to-cathode discharge when the anode voltage (Va) is set to 140 V, the starter anode must draw a maximum current of 100 µA.

Conduction Voltage Drops

Once the tube is triggered and conducting, the voltage drops across the internal discharge paths are maintained at stable levels:

  • Starter Anode to Cathode Voltage Drop: The voltage drop across the starter-cathode path during conduction is 60 V.
  • Anode to Cathode Voltage Drop: The voltage drop across the main anode-cathode conduction path is 70 V.

Cathode Current Ratings

To ensure the longevity of the cold cathode and prevent damage, the current through the cathode must not exceed the following limits:

  • Maximum Peak Cathode Current: 100 mA
  • Maximum D.C. Cathode Current: 25 mA

Technical Summary

The 1267 is an octal-based, cold-cathode gas-filled triode with an overall length of 100 mm and a diameter of 31 mm. It features a three-electrode structure with the cathode connected to Pin 2, the anode to Pin 5, and the grid (starter anode) to Pin 7. Operating without a heater, the device relies on gas ionization, featuring a starter breakdown voltage range of 70 V to 90 V and a main anode-to-cathode conduction drop of 70 V. It is rated for a maximum continuous D.C. cathode current of 25 mA and a peak cathode current of 100 mA.

Socket description

International Octal

General specifications

Tube and section characteristics

Properties common to every published source and operating point.

Heater and base

Base
-
Socket code
IO
Base pins
8
Nominal heater voltage
-
Nominal heater current
-
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

Thyratron

X-ray radiationInterelectrode capacitances
Max plate voltage
225 V
Max cathode current
25 mA

Mullard 1951 p.163 1267 cold-cathode gas-filled switching triode, provisionally classified Thyratron by switching function (not necessarily conventional hot-cathode thyratron). Maximum operating anode voltage 225 V when starter anode connected to cathode. Starter-anode-to-cathode breakdown 70–90 V; max starter current 100 µA at main anode 140 V for breakdown; starter path drop 60 V, main anode-cathode drop 70 V. Max peak cathode current 0.1 A, max DC cathode current 0.025 A (promoted max_cathode_current is continuous DC rating). No heater. Octal base cathode pin2, anode pin5, starter pin7.

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

1951 Mullard Valve and Service Manual

Published operating points and test conditions from this source.

SECTION 1

Thyratron

Other

  • Maximum Operating Anode Voltage

    225 V

    Starter anode connected to cathode

  • Maximum Starter Anode Current

    100 uA

    Anode breakdown; Vs=140V

  • Maximum Peak Cathode Current

    100 mA

  • Maximum DC Cathode Current

    25 mA

Characteristics

  • Starter Anode-Cathode Breakdown Voltage Minimum

    70 V

  • Starter Anode-Cathode Breakdown Voltage Maximum

    90 V

  • Starter Anode-Cathode Voltage Drop

    60 V

  • Anode-Cathode Voltage Drop

    70 V