Voltage - Triode (with diode, heptode or hexode) ·Diode-Diode-Triode
Double-diode very-high-mu triode for detector, AVC, and voltage-amplifier service. The paired diodes provide signal and control-voltage rectification while the high-gain triode supplies substantial amplification following the detector stage.
The 14X7 is a multi-unit vacuum tube containing a single high-mu triode and two independent diode units within a single envelope. It is designed for use in receiving equipment, particularly in applications requiring detection, automatic volume control (AVC), and audio amplification. The tube features a Loktal 8-pin base and is designed to operate with a nominal heater supply of either 12.6 V or 14.0 V, though specific operating conditions are also documented at other heater voltages.
The 14X7 is constructed with coated unipotential cathodes. It is housed in a T-9 glass bulb with an 8-pin Loktal base. The physical dimensions of the tube are:
The tube can be mounted in any position.
The 14X7 uses the 8BZ (or 8BZ-L-4) basing arrangement. The pin connections, viewed from the bottom of the base, are as follows:
This configuration shows that while Diode #1 shares its cathode (Cathode #1) with the triode unit, Diode #2 has an independent cathode (Cathode #2), allowing for flexible circuit configurations.
The heater of the 14X7 can be operated on either AC or DC. The nominal ratings and average characteristics of the heater are documented with slight variations:
The triode section of the 14X7 is a high-mu voltage amplifier.
Under Class A amplifier conditions, the average characteristics of the triode unit are documented at two distinct operating points:
| Parameter | Operating Point A | Operating Point B |
|---|---|---|
| Heater Voltage | 12.6 V | 12.6 V |
| Heater Current | 0.150 A | 0.150 A |
| Plate Voltage | 100 V | 250 V |
| Grid Voltage | 0 V | -1.0 V |
| Plate Current | 1.2 mA | 1.9 mA |
| Plate Resistance | 85,000 Ω | 67,000 Ω |
| Transconductance | 1,000 µmhos | 1,500 µmhos |
| Amplification Factor (μ) | 85 | 100 |
At the 250 V plate operating point, the triode exhibits a high amplification factor of 100 and a transconductance of 1,500 µmhos, with a plate current of 1.9 mA.
The 14X7 contains two diode units. Their characteristics are specified as follows:
The direct interelectrode capacitances of the 14X7, measured without an external shield, are:
These low capacitances help minimize unwanted coupling between the diode detector circuits and the high-gain triode grid.
The 14X7 is highly suited for resistance-coupled Class A amplifier service. The manufacturer documents specific typical operating conditions for a zero-bias configuration. Notably, these conditions are specified at a heater voltage of 6.3 V:
| Parameter | Condition 1 | Condition 2 |
|---|---|---|
| Heater Voltage | 6.3 V | 6.3 V |
| Plate Supply Voltage | 100 V | 300 V |
| Grid Leak of Following Stage | 10 MΩ | 10 MΩ |
| Load Resistance | 0.25 MΩ | 0.25 MΩ |
| Coupling Capacitance | 0.01 to 0.005 µµF | 0.01 to 0.005 µµF |
| Grid Resistor of Following Tube | 1.0 MΩ | 1.0 MΩ |
| External Grid Circuit Impedance | 0 MΩ | 0 MΩ |
| Voltage Gain | 30 | 40 |
| Voltage Output (RMS) at 5% Distortion | 6 V | 30 V |
These operating points demonstrate that even with a lower plate supply voltage of 100 V, a voltage gain of 30 is achievable, rising to 40 when the plate supply is increased to 300 V. The corresponding RMS voltage output at 5% distortion increases from 6 V to 30 V.
The 14X7 is a Loktal-base, duplex-diode high-mu triode designed for detector, AVC, and audio amplifier service. It features a heater rated nominally at 14.0 V (0.15 A) or 12.6 V (0.150 A), with additional zero-bias resistance-coupled amplifier operating points documented at 6.3 V. The high-mu triode section provides an amplification factor of up to 100, a transconductance of 1,500 µmhos, and a plate resistance of 67,000 Ω under typical Class A conditions. The two diode units are designed for efficient detection, with one diode sharing a cathode with the triode and the other having an independent cathode connection.
Loctal 8-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.
3 physical sections, each with unique specifications.
Section 1
No fixed ratings are recorded for this section.
Promoted ratings/characteristics read from the approved National Union datasheet.
Section 2
No fixed ratings are recorded for this section.
Promoted ratings/characteristics read from the approved National Union datasheet.
Section 3
Promoted ratings/characteristics read from the approved National Union datasheet.
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.
Plate voltage
250 V
ClassA
Control-grid voltage
-1 V
ClassA
Plate current
1.9 mA
ClassA
Plate resistance
67000 Ω
ClassA
Transconductance
1500 µS
ClassA
Amplification factor
100
ClassA