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11D12

Dual low-mu power triode designed for booster-scanning circuits and series-regulator service in DC power supplies. Its sections withstand severe pulse conditions, including kilovolt-level inverse and control-grid pulse voltages.

Directly heatedCold cathodeCommon cathodeDissimilar

Sections: 2
Base: -
Socket code: -
Base pins: 8
Nominal heater: 6.3 V / 2.5 A

Description

11D12 — Low-Mu Power Double Triode Vacuum Tube

The 11D12 is an indirectly heated, low-mu power double triode designed with separate cathodes for each section. It is specifically engineered for demanding roles such as booster scanning circuits and as a series regulator in DC power supply units. Produced under the Ediswan brand by Associated Electrical Industries (AEI) Limited, this tentative design provides high current capability and substantial power handling within a single envelope.

Physical Dimensions, Mounting, and Base Configuration

The 11D12 is housed in a glass bulb with a maximum overall length of 103 mm, a maximum seated height of 88.5 mm, and a maximum base diameter of 43.5 mm. The tube is designed for unrestricted mounting positions, allowing flexibility in physical chassis layouts.

The tube utilizes a 108 base. The pin connections, viewed from the free end of the pins, are arranged as follows:

Pin	Connection	Symbol
Pin 1	Grid (Section 1)	g'
Pin 2	Anode (Section 1)	a'
Pin 3	Cathode (Section 1)	k'
Pin 4	Grid (Section 2)	g''
Pin 5	Anode (Section 2)	a''
Pin 6	Cathode (Section 2)	k''
Pin 7	Heater	h
Pin 8	Heater	h

Heater and Electrical Characteristics

The 11D12 features a high-power heater designed to support the heavy emission requirements of its two triode sections. The heater operates at a nominal voltage of 6.3 V and draws a nominal current of 2.5 A.

Calculated Heater Power: 15.75 W (derived from the nominal inputs of 6.3 V and 2.5 A).

Section Characteristics

Each independent triode section exhibits low anode resistance and low amplification factor, optimized for high-current regulation and booster scanning applications. The typical characteristics per section, measured at the absolute limit of anode current and dissipation, are:

Parameter	Value
Anode Supply Voltage ( $V_{a(b)}$ )	135 V
Anode Current ( $I_a$ )	125 mA
Cathode Bias Resistance ( $R_k$ )	250 Ω
Mutual Conductance ( $g_m$ )	7.0 mA/V
Amplification Factor ( $\mu$ )	2.0
Valve Anode Resistance ( $r_a$ , approx.)	280 Ω

The relationship between these parameters is consistent with standard triode behavior, where $g_m \times r_a \approx \mu$ (calculated as $0.007\text{ A/V} \times 280\ \Omega = 1.96$, which closely approximates the nominal amplification factor of 2.0).

Absolute Maximum Ratings and Circuit Constraints

The absolute maximum ratings for the 11D12 must be strictly observed to prevent premature failure or damage. These ratings apply to each section individually unless otherwise specified:

Rating Parameter	Absolute Maximum Value
Maximum Anode Supply Voltage ( $V_{a(b)\text{max}}$ )	550 V
Maximum Anode Voltage ( $V_{a(\text{max})}$ )	250 V
Maximum Peak Inverse Voltage (Booster Service)	3.0 kV *
Maximum Negative Control Grid Pulse Voltage (Booster Service)	2.3 kV *
Maximum Cathode Current ( $I_{k(\text{max})}$ )	125 mA
Maximum Anode Dissipation ( $P_{a(\text{max})}$ )	13 W
Maximum Heater-to-Cathode Voltage ( $V_{h-k(\text{max})}$ )	300 V †
Maximum Bulb Temperature ( $T_{\text{bulb}(\text{max})}$ )	230 °C

* Booster scanning service limits apply to a maximum pulse duration of 15% of one cycle, with an absolute maximum duration of 15 µs. † Operation is explicitly not recommended with a damper pulse between the heater and cathode.

Grid-to-Cathode Resistance Limits

Cathode Bias: The maximum allowable resistance between the grid and cathode is 1.0 MΩ per section.
Fixed Bias: The maximum allowable resistance between the grid and cathode is 0.1 MΩ per section.

Circuit Design and Biasing Guidelines

Specific circuit precautions must be followed when operating the 11D12 under various biasing and configuration states:

Fixed Bias Protection: When utilizing fixed bias, the anode circuit must contain a protective resistance designed to provide a minimum voltage drop of 15 V DC under normal operating conditions.
Parallel Operation: If two or more triode sections are operated in parallel at dissipations approaching their rated maximums, separate anode and cathode resistors must be employed to assist in proper load sharing.
Combined Bias: When a combination of fixed and cathode bias is used, the cathode bias portion must provide a minimum value of 7.5 V DC under normal operating conditions, with a grid-to-cathode resistance of 100 kΩ.
Booster Scanning Restriction: The use of fixed bias is not recommended when the valve is employed in booster scanning circuits.

Inter-electrode Capacitances

The inter-electrode capacitances for each section of the 11D12 are measured in a fully shielded socket without an external can. These values define the capacitive coupling between elements:

Capacitance Parameter	Value
Anode to Grid ( $C_{a-g}$ )	7.3 pF
Heater to Cathode ( $C_{h-k}$ )	9.6 pF
Anode 2 to Anode 1 ( $C_{a''-a'}$ )	2.7 pF
Grid 2 to Grid 1 ( $C_{g''-g'}$ )	0.25 pF
Grid 1 or Grid 2 to Earth ( $C_{in}$ )	6.9 pF
Anode 1 or Anode 2 to Earth ( $C_{out}$ )	2.5 pF

The low grid-to-grid capacitance ( $C_{g''-g'} = 0.25\text{ pF}$ ) indicates relatively good isolation between the control grids of the two sections, despite their proximity within the same envelope. However, the anode-to-anode capacitance ( $C_{a''-a'}$ ) is 2.7 pF, which must be accounted for in high-frequency or pulse-based circuit designs.

Technical Summary

The 11D12 is a robust, high-current, low-mu power double triode featuring separate cathodes and a common 6.3 V, 2.5 A heater. Designed for heavy-duty applications, it is highly suited for booster scanning circuits and series regulation in DC power supplies. Each section is capable of dissipating up to 13 W and handling up to 125 mA of continuous cathode current. With an exceptionally low anode resistance of approximately 280 Ω and an amplification factor of 2.0 at its operating limit, the 11D12 provides the low-impedance drive necessary for efficient power control and voltage regulation.

General specifications

Tube and section characteristics

Properties common to every published source and operating point.

Heater and base

Base: -
Socket code: -
Base pins: 8
Nominal heater voltage: 6.3 V
Nominal heater current: 2.5 A
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: 280 Ω
Transconductance: 0.007 S
Amplification factor: 2
Max plate voltage: 550 V
Max plate dissipation: 13 W
Max cathode current: 125 mA

Representative section for repeated identical sections.

Section 2

Triode

X-ray radiationInterelectrode capacitances

Plate resistance: 280 Ω
Transconductance: 0.007 S
Amplification factor: 2
Max plate voltage: 550 V
Max plate dissipation: 13 W
Max cathode current: 125 mA

Identical second physical section; duplicated from representative section per physical-section-row policy.

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 AEI Industrial Valves

Published operating points and test conditions from this source.

SECTION 1

Triode

Other

Maximum anode supply voltage
550 V
EachSection
Maximum peak inverse voltage
3 kV
BoosterScanning
Maximum negative control-grid pulse voltage
2.3 kV
BoosterScanning
Maximum heater-cathode voltage
300 V
EachSection

Capacitance

Anode-grid capacitance
7.3 pF
EachSection
Heater-cathode capacitance
9.6 pF
EachSection
Inter-anode capacitance
2.7 pF
BetweenSections
Inter-grid capacitance
0.25 pF
BetweenSections

Data set 02

1961 Associated Electrical Industries

Published operating points and test conditions from this source.

SECTION 1

Triode

Other

Maximum anode supply voltage
550 V
EachSection
Maximum peak inverse voltage
3 kV
BoosterScanning
Maximum negative control-grid pulse voltage
2.3 kV
BoosterScanning
Maximum heater-cathode voltage
300 V
EachSection

Capacitance

Anode-grid capacitance
7.3 pF
EachSection
Heater-cathode capacitance
9.6 pF
EachSection
Inter-anode capacitance
2.7 pF
BetweenSections
Inter-grid capacitance
0.25 pF
BetweenSections