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15J12

Directly heated forced-air-cooled triode designed specifically for industrial RF-heating equipment, using a thoriated-tungsten filament for substantial continuous high-frequency power.

Directly heatedCold cathodeCommon cathodeDissimilar

Sections: 1
Base: -
Socket code: -
Base pins: -
Nominal heater: 6.3 V / 32.5 A

Description

15J12 — Forced-Air Cooled Power Triode

A directly heated, forced-air cooled power triode designed primarily for industrial radio-frequency (r.f.) heating applications and high-power amplification.

Overview

The 15J12 is a heavy-duty power triode featuring a directly heated thoriated tungsten filament and an external anode design. Developed by Associated Electrical Industries Limited (AEI) under the Ediswan brand, this tube is primarily engineered for industrial r.f. heating equipment, high-frequency oscillation, and class-level power amplification. The device is characterized by its robust construction, high power handling capabilities, and the requirement for forced-air cooling to manage anode dissipation.

Filament and Cooling Requirements

The 15J12 utilizes a high-current, directly heated thoriated tungsten filament. Due to the substantial power consumed by the filament, proper electrical contact and thermal management are critical.

Filament Parameter	Value
Nominal Filament Voltage ( $V_f$ )	6.3 V
Nominal Filament Current ( $I_f$ )	32.5 A
Calculated Filament Power ( $P_f$ )	204.75 W

Note: The filament power of 204.75 W is a calculation derived from the nominal voltage and current (6.3 V x 32.5 A).

Cooling Specifications

To maintain safe operating temperatures at maximum ratings, forced-air cooling is mandatory:

Anode Cooling: A minimum forced-air flow of 60 cubic feet per minute (ft³/min) is required. This air blast must be directed horizontally at the external anode structure.
Pin and Seal Cooling: At higher operating frequencies, a low-velocity auxiliary air blast directed onto the filament and grid pins is recommended to prevent overheating of the metal-to-glass seals and pins.

Physical Construction, Basing, and Mounting

The physical design of the 15J12 is optimized for high-power r.f. environments. It features an external anode integrated with a transverse-finned radiator assembly for efficient heat transfer.

Mechanical Dimensions

Maximum Overall Length: 200 mm
Maximum Radiator Diameter: 102 mm
Radiator Assembly Length: 175 mm (maximum)
Base Diameter: 74 mm (nominal)
Pin Length: 23 mm (nominal), with an 18 mm minimum exposure
Pin Diameter: 9 mm

Basing and Electrical Connections

The tube uses a special base configuration with four heavy-duty pins, each measuring 9 mm in diameter. The pinout consists of:

Filament (f): Two pins dedicated to the thoriated tungsten filament.
Grid (g): Two separate pins connected to the control grid.
Anode: Connection is made directly to the external radiator body.

To prevent localized overheating and excessive r.f. current concentration in a single terminal, it is essential to connect the external circuit to both grid pins simultaneously when operating at higher frequencies. This dual-connection design distributes the r.f. current evenly between the two pins.

Mounting Position

The 15J12 must be mounted vertically with the anode pointing upwards. It must also be protected against excessive mechanical vibration and shock to preserve the integrity of the internal filament structure and glass-to-metal seals.

Electrical Ratings and Characteristics

The maximum ratings represent absolute limits that must not be exceeded under any operational state.

Absolute Maximum Ratings

Maximum Anode Voltage ( $V_{a(max)}$ ): 7.0 kV
Maximum Anode Dissipation ( $P_{a(max)}$ ): 1.3 kW
Maximum Peak Cathode Current ( $i_{k(pk)max}$ ): 4.0 A
Maximum Operating Frequency ( $f_{max}$ ): 60 Mc/s (at full ratings)

Inter-Electrode Capacitances

Anode to Grid ( $C_{a-g}$ ): 11 pF
Grid to Filament ( $C_{g-f}$ ): 13 pF
Anode to Filament ( $C_{a-f}$ ): 0.6 pF

Static Characteristics

Measured at an anode voltage ( $V_a$ ) of 4.0 kV and an anode current ( $I_a$ ) of 190 mA:

Mutual Conductance ( $g_m$ ): 5.1 mA/V
Amplification Factor ( $\mu$ ): 22

Typical Operating Conditions

The 15J12 can be operated in several classes of service. The published operating points represent maximum conditions for each specific class.

Class B1 Audio Amplifier (Push-Pull Operation, Per Valve)

In Class B1 service, the grid is not driven into the positive region (no grid current flows).

Parameter	Value
Anode Voltage ( $V_a$ )	6.0 kV
Anode Current R.M.S. ( $I_{a(r.m.s.)}$ )	0.6 A
Power Input ( $P_{in}$ )	2.2 kW
Power Output ( $P_{out}$ )	0.9 kW
Anode Dissipation ( $P_a$ )	1.3 kW
Anode Efficiency	40%
Negative Grid Bias Voltage ( $V_g$ )	-225 V
Peak Signal Voltage ( $V_{sig(pk)}$ )	225 V

Class C Single Phase Full Wave (No Smoothing)

This operating mode is typical for industrial power supplies where raw, unsmoothed rectified AC is applied to the anode.

Parameter	Mean	R.M.S.	Peak
Anode Voltage ( $V_a$ )	3.8 kV	4.25 kV	6.0 kV
Negative Grid Bias Voltage ( $V_g$ )	-80 V	—	—
Positive Grid Voltage ( $V_{sig}$ )	—	—	154 V
Grid Resistance ( $R_g$ )	0.7 kΩ	—	—
Mean Anode Current ( $I_{a(av)}$ )	730 mA	—	—
Mean Grid Current ( $I_{g(av)}$ )	120 mA	—	—
Peak Cathode Current ( $i_{k(pk)}$ )	2.5 A	2.8 A	4.0 A
Peak Anode Current ( $i_{a(pk)}$ )	—	—	1.9 A
Peak Grid Current ( $i_{g(pk)}$ )	—	—	0.6 A
Anode Dissipation ( $P_a$ )	1.3 kW	—	—
Grid Drive Power	30 W	—	—
Grid Dissipation ( $P_g$ )	20 W	—	—
Anode Efficiency	61%	—	—
Power Output (Amplifier) ( $P_{out}$ )	2.1 kW	—	—
Power Output (Oscillator, 100% Transfer)	2.1 kW	—	—
Power Output (Oscillator, 85% Transfer)	1.8 kW	—	—

Class C 3-Phase Rectified or D.C.

For operation with a smooth DC supply or a three-phase rectified supply, three distinct anode voltage operating points are established:

Parameter	4.0 kV Supply	5.0 kV Supply	6.0 kV Supply
Anode Voltage ( $V_a$ )	4.0 kV	5.0 kV	6.0 kV
Negative Grid Bias Voltage ( $V_g$ )	-140 V	-220 V	-300 V
Positive Grid Voltage ( $V_{sig}$ )	270 V	270 V	270 V
Grid Resistance ( $R_g$ )	553 Ω	982 Ω	1400 Ω
Mean Anode Current ( $I_{a(av)}$ )	1068 mA	993 mA	930 mA
Mean Grid Current ( $I_{g(av)}$ )	253 mA	224 mA	204 mA
Peak Cathode Current ( $i_{k(pk)}$ )	4.0 A	4.0 A	4.0 A
Peak Anode Current ( $i_{a(pk)}$ )	3.0 A	3.0 A	3.0 A
Peak Grid Current ( $i_{g(pk)}$ )	1.0 A	1.0 A	1.0 A
Anode Dissipation ( $P_a$ )	1.3 kW	1.3 kW	1.3 kW
Grid Drive Power	104 W	100 W	108 W
Grid Dissipation ( $P_g$ )	60 W	50 W	48 W
Anode Efficiency	69%	73%	76%
Power Output (Amplifier) ( $P_{out}$ )	2.9 kW	3.6 kW	4.2 kW
Power Output (Oscillator, 100% Transfer)	2.8 kW	3.5 kW	4.1 kW
Power Output (Oscillator, 85% Transfer)	2.4 kW	3.0 kW	3.5 kW

Installation and Operating Guidelines

Because the typical operating points utilize the tube near its absolute maximum ratings, strict control of operating conditions is required. Linear interpolation between the documented anode voltage steps is permissible.

Circuit Protection

In Class C self-oscillator service, precautions must be taken to protect the tube against excessive mains voltage variations. The following safety devices should be integrated into the system:

Current Overload Trips: Installed in both the anode and grid circuits to interrupt power in the event of an overcurrent condition.
Undercurrent Trip: Installed in the grid circuit to protect the tube from loss of bias, which would otherwise lead to runaway anode dissipation.

Industrial R.F. Heating Considerations

In industrial environments, it is often impractical to implement perfect voltage regulation and load matching. Under these conditions, the operating parameters must be reduced. This derating accommodates:

Widely fluctuating load impedances (common during the heating cycle of various materials).
Poor high-tension (h.t.) power supply regulation.
Mains supply voltage variations.

Because each industrial installation presents unique load-coupling and regulation challenges, no universal set of rules applies, and operating points must be adjusted empirically to keep the tube within its 1.3 kW anode dissipation limit.

Technical Summary

The 15J12 is a high-power, forced-air cooled triode designed for demanding industrial r.f. heating and amplification roles. Operating with a 6.3 V, 32.5 A thoriated tungsten filament, the tube provides an amplification factor of 22 and a mutual conductance of 5.1 mA/V under static conditions. It is rated for a maximum anode voltage of 7.0 kV and an anode dissipation of 1.3 kW, supported by a mandatory horizontal forced-air flow of 60 ft³/min. With its dual grid-pin design and external anode, the 15J12 delivers up to 4.2 kW of r.f. power output in Class C configurations, making it a highly capable component for heavy-duty industrial and high-frequency applications.

General specifications

Tube and section characteristics

Properties common to every published source and operating point.

Heater and base

Base: -
Socket code: -
Base pins: -
Nominal heater voltage: 6.3 V
Nominal heater current: 32.5 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

1 physical section, each with unique specifications.

Section 1

Triode

X-ray radiationInterelectrode capacitances

Transconductance: 0.0051 S
Amplification factor: 22
Max plate voltage: 7000 V
Max plate dissipation: 1300 W
Max cathode current: 4 A

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 operating frequency
60 MHz

Cooling

Minimum air flow at maximum dissipation
60 ft3/min

Capacitance

Anode-grid capacitance
11 pF
Grid-filament capacitance
13 pF

Data set 02

1961 Associated Electrical Industries

Published operating points and test conditions from this source.

SECTION 1

Triode

Other

Maximum operating frequency
60 MHz

Cooling

Minimum air flow at maximum dissipation
60 ft3/min

Capacitance

Anode-grid capacitance
11 pF
Grid-filament capacitance
13 pF