Voltage - Dual Triode (similar) ·Triode-Triode
Twin triode intended for general voltage-amplifier and related signal applications, using two triode sections in a series-heater form suited to equipment with controlled heater strings.
An industrial-grade, indirectly heated double triode featuring separate cathodes and an octal base, designed for high-reliability applications in aircraft and industrial equipment.
The 13D1 is a specialized double triode vacuum tube designed by Brimar for use in aircraft and industrial systems where operational reliability is critical. It was introduced as a direct replacement for and supersedes the 25SN7GT designation.
The 13D1 contains two independent triode sections with separate cathodes, sharing a common heater. Except for its specific heater ratings, the electrical characteristics of the 13D1 are nominally identical to those of the standard 6SN7GT twin triode. This allows the 13D1 to be used in similar circuit topologies—such as voltage amplifiers, phase inverters, and oscillators—provided the heater supply is configured for its specific voltage and current requirements.
The 13D1 is constructed with two separate triode structures housed in a glass envelope with an eight-pin octal base. The separate cathodes allow each triode section to be biased independently, preventing unwanted coupling between stages.
The heater of the 13D1 is designed for series-string or higher-voltage industrial power supplies, distinguishing it from the 6.3 V heater of the 6SN7GT.
The tube utilizes a standard octal base with the following pin assignments (viewed from the underside of the base):
| Pin | Electrode Connection | Symbol |
|---|---|---|
| 1 | Grid, Triode Section 2 | g'' |
| 2 | Anode, Triode Section 2 | a'' |
| 3 | Cathode, Triode Section 2 | k'' |
| 4 | Grid, Triode Section 1 | g' |
| 5 | Anode, Triode Section 1 | a' |
| 6 | Cathode, Triode Section 1 | k' |
| 7 | Heater | h |
| 8 | Heater | h |
The 13D1 operates as a medium-mu double triode. The manufacturer specifies two typical Class A operating points for each individual triode section:
| Parameter | Operating Point A | Operating Point B |
|---|---|---|
| Anode Voltage | 100 V | 250 V |
| Grid Voltage | 0 V | -8 V |
| Cathode Bias Resistor | — | 1,100 Ω |
| Anode Current | 10.6 mA | 9.0 mA |
| Anode Impedance | 8,000 Ω | 7,700 Ω |
| Mutual Conductance | 2.5 mA/V | 2.6 mA/V |
| Amplification Factor (μ) | 20 | 20 |
The relationship between the parameters is consistent with standard triode operation, where the amplification factor (μ) is approximately equal to the product of mutual conductance (g_m) and anode impedance (r_p). For Operating Point B, this is illustrated by the calculation:
μ ≈ 0.0026 A/V × 7,700 Ω = 20.02
For further detailed characteristic curves and extended operating data, the tube shares nominal behavior with the 6SN7GT.
The 13D1 was specifically engineered to meet the demanding environmental and reliability requirements of aviation and industrial systems. It directly supersedes the 25SN7GT and can be used as a drop-in replacement in any circuit designed for that type.
Because its electrical characteristics (excluding the heater) are nominally identical to the 6SN7GT, the 13D1 can perform the same circuit functions—such as voltage amplification, phase inversion, and oscillation—provided the power supply is configured to deliver the required 25 V, 0.15 A heater service instead of the 6.3 V, 0.6 A service required by the 6SN7GT.
Small-button Noval 9-contact
General specifications
Properties common to every published source and operating point.
Electrical assignments shared by every tube using this base designation.
No verified pinout is recorded for this base designation.
2 physical sections, each with unique specifications.
Section 1
Representative of two identical sections.
Section 2
Second identical physical triode section; added to align rows with SectionCount.
Source-dependent data
Each block preserves the test conditions and published values from one reference. Values from different sources are intentionally kept separate.
Data set 01
Published operating points and test conditions from this source.
Anode Voltage
250 V
Each section
Anode Current
9 mA
Each section
Grid Voltage
-8 V
Each section
Cathode Bias Resistor
1100 ohm
Each section