Voltage - Dual Triode (similar) ·Triode-Triode
High-mu twin triode designed for low-level high-fidelity audio amplification, with manufacturer operating data emphasizing resistance-coupled Class-A service and favorable signal-to-noise performance.
The 12DM7 is a miniature, low-hum, high-mu duotriode vacuum tube designed for voltage amplification in low-level stages of high-fidelity amplifiers and other audio equipment. It contains two independent triode sections within a single glass envelope, sharing a common heater with a center tap that allows for either series or parallel heater operation. With an amplification factor of 100, the 12DM7 is optimized for high-gain applications where minimizing hum and noise is critical.
The 12DM7 is constructed in a T-6 1/2 miniature glass bulb. It features a standard 9-pin miniature base (designated as base 9A). The tube has a maximum overall height of 2 3/16 inches, a maximum seated height of 1 15/16 inches, and a maximum diameter of 7/8 inches. It is designed to be operated in any mounting position.
The 9A base pinout configuration provides independent connections for the electrodes of both triode sections, alongside a center-tapped heater:
| Pin Number | Electrode Connection |
|---|---|
| 1 | Plate (Section 2) |
| 2 | Control Grid (Section 2) |
| 3 | Cathode (Section 2) |
| 4 | Heater |
| 5 | Heater |
| 6 | Plate (Section 1) |
| 7 | Control Grid (Section 1) |
| 8 | Cathode (Section 1) |
| 9 | Heater Tap |
This layout allows the two triode sections to be biased and operated independently, provided that heater-to-cathode voltage limits are respected.
The heater of the 12DM7 is designed for versatility, supporting both series and parallel wiring configurations using AC or DC power. The center tap connected to Pin 9 allows the heater filaments to be operated at either a nominal 12.6 V or 6.3 V.
| Heater Configuration | Voltage (AC or DC) | Current |
|---|---|---|
| Series | 12.6 V | 0.13 A |
| Parallel | 6.3 V | 0.26 A |
The direct interelectrode capacitances of the two sections are highly symmetrical, with minor variations in output capacitance. These values are measured without an external shield:
| Capacitance Parameter | Section 1 | Section 2 |
|---|---|---|
| Grid to Plate (G to P) | 1.7 µµF | 1.7 µµF |
| Input (G to K+H) | 1.6 µµF | 1.6 µµF |
| Output (P to K+H) | 0.46 µµF | 0.34 µµF |
Under Class A amplifier service, the 12DM7 exhibits high voltage gain (amplification factor of 100) and relatively high plate resistance. The typical operating parameters for each independent triode section are documented at two distinct plate voltage points:
| Parameter | Operating Point I | Operating Point II |
|---|---|---|
| Plate Voltage | 100 V | 250 V |
| Control Grid Voltage | -1 V | -2 V |
| Plate Resistance (Approx.) | 80 kΩ | 62.5 kΩ |
| Transconductance | 1250 µmhos | 1600 µmhos |
| Amplification Factor | 100 | 100 |
| Plate Current | 0.5 mA | 1.2 mA |
The 12DM7 is specifically engineered for low-hum and low-noise performance in audio applications. When operated in a resistance-coupled (R-C) amplifier stage with a gain of 63 dB, the signal-to-noise ratio is specified as 57 dB down. This makes the tube highly effective for processing low-level audio signals without introducing objectionable hum.
The ratings for the 12DM7 are established under the Design Maximum System. These limits must not be exceeded under the worst-case operating conditions to ensure reliable operation and longevity of the tube. The ratings apply to each individual triode section:
| Rating Parameter | Limit Value | Unit |
|---|---|---|
| Maximum Plate Voltage | 330 | Volts |
| Maximum Negative Control Grid Voltage (-DC) | 50 | Volts |
| Maximum Positive Control Grid Voltage (+DC) | 0 | Volts |
| Maximum Plate Dissipation | 1.1 | Watts |
| Maximum Peak Heater-Cathode Voltage (Heater Negative to Cathode) | 180 | Volts |
| Maximum Peak Heater-Cathode Voltage (Heater Positive to Cathode) | 180 | Volts |
The 12DM7 is a high-mu, low-hum duotriode housed in a 9-pin miniature T-6 1/2 glass envelope. Featuring a center-tapped heater that supports 12.6 V series (0.13 A) or 6.3 V parallel (0.26 A) operation, it provides two independent, high-gain triode sections. Each section delivers an amplification factor of 100, with transconductance ranging from 1250 to 1600 µmhos and plate resistance between 62.5 kΩ and 80 kΩ depending on the operating point. With a design-maximum plate voltage rating of 330 V and a plate dissipation limit of 1.1 W per section, the 12DM7 is highly optimized for low-level, low-noise preamplification in high-fidelity audio systems.
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 row for identical repeated diode/triode sections.
Section 2
Physical triode row restored under current one-row-per-physical-section policy.
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.
PlateResistanceAtLowerCurrent
80000 ohm
TransconductanceAtLowerCurrent
1250 uS
Service
Low-level high-fidelity audio amplifier
Data set 02
Published operating points and test conditions from this source.
Plate resistance at 100 V
80000 ohm
ClassA
Transconductance at 100 V
1250 µS
ClassA
Plate current at 100 V
0.5 mA
ClassA
Signal-to-noise ratio in 63 dB F-C amplifier
57 dB down
AudioService
Plate voltage
250 V
ClassA
Grid voltage
-2 V
ClassA
Plate current
1.2 mA
ClassA