Voltage - Triode (with diode, heptode or hexode) ·Hexode-Triode
Triode-hexode frequency converter for superheterodyne receivers. The triode serves as local oscillator while the remote-cutoff hexode performs mixing, combining oscillator and converter functions with high output resistance for good circuit isolation.
An indirectly heated multi-unit vacuum tube containing a triode and a remote cut-off hexode, designed for frequency converter and mixer applications in radio receivers.
The 14K7 is a multi-unit frequency converter tube manufactured by N.V. Philips' Gloeilampenfabrieken. It combines a triode section and a hexode section within a single glass envelope. The hexode section is designed with remote cut-off characteristics, allowing for effective automatic gain control (AGC) or automatic volume control (AVC) without introducing significant distortion. In typical receiver designs, the triode section operates as the local oscillator, while the hexode section functions as the mixer/converter.
The 14K7 is constructed with a glass bulb and an E8-30 base. It can be mounted and operated in any position.
The physical dimensions of the device are:
The tube utilizes the 8GY basing arrangement. The pin connections, viewed from the underside of the base, are as follows:
| Pin | Connection |
|---|---|
| Pin 1 | Heater |
| Pin 2 | Hexode Plate |
| Pin 3 | Triode Plate |
| Pin 4 | Hexode Grid No. 3, Triode Grid (internally connected) |
| Pin 5 | Hexode Grids No. 2 & No. 4 |
| Pin 6 | Hexode Grid No. 1 |
| Pin 7 | Cathode |
| Pin 8 | Heater |
The internal connection between the hexode's third grid (Grid No. 3) and the triode's control grid on Pin 4 simplifies circuit layout by directly injecting the local oscillator signal into the mixing structure of the hexode.
The 14K7 features a coated unipotential cathode shared between both the triode and hexode sections. The heater is designed for series or parallel operation with the following nominal electrical ratings:
To prevent insulation breakdown and ensure reliable operation, the potential difference and resistance between the heater and cathode must be kept within the following limits:
The electrical characteristics of the 14K7 are specified separately for the hexode and triode sections under typical operating conditions.
Under typical operating conditions, the hexode section exhibits the following characteristics:
The triode section operates with the following typical characteristics:
The maximum ratings for the 14K7 are defined under the design centre rating system. These limits must not be exceeded to maintain tube longevity and performance.
The interelectrode capacitances of the 14K7 determine its performance at high frequencies. The capacitances are detailed below for both sections and between the sections:
The operational behavior of the 14K7 is further illustrated by its characteristic curves, which detail the relationships between electrode voltages, currents, and transconductance.
The triode section's plate family curves show plate current plotted against plate voltage for grid bias values ranging from 0 V down to -12 V in 2 V increments. At a grid bias of 0 V, the plate current rises rapidly with plate voltage, reaching approximately 10 mA at 100 V and exceeding 20 mA as the plate voltage approaches 150 V.
Additionally, at a fixed plate voltage of 100 V, the transconductance and plate current curves plotted against grid bias demonstrate that both parameters fall smoothly as the grid bias becomes more negative. The transconductance starts at 2,800 µmhos at 0 V bias and approaches zero near -10 V, while the plate current drops from 10 mA to zero over the same bias range.
The hexode section curves illustrate the remote cut-off characteristics of the mixer. Plate current and transconductance are plotted against Grid No. 1 bias for plate voltages between 170 V and 200 V, under typical oscillator conditions (oscillator grid leak of 47,000 ̩ and an oscillator grid current of 200 µA).
Curves are provided for various fixed Grids No. 2 and 4 voltages (40 V, 70 V, 100 V, 130 V, and 160 V), as well as for supply configurations using a potentiometer network (18,000 ̩ + 27,000 ̩) at supply voltages of 170 V and 200 V. These curves demonstrate that the transconductance decreases gradually from around 750–1000 µmhos at low bias values down to approximately 1 µmho at a Grid No. 1 bias of -40 V. This extended, smooth cut-off characteristic allows the tube to handle a wide range of input signal levels without cross-modulation or distortion when AGC voltage is applied.
The 14K7 is an E8-30 based, indirectly heated triode-hexode converter featuring a 14 V, 0.1 A heater and a shared cathode. It is designed for frequency conversion and mixing applications in radio receivers. The hexode section provides a remote cut-off characteristic with a conversion transconductance of 750 µmhos at a plate voltage of 200 V and screen voltage of 85 V, which can be controlled down to 7.5 µmhos at a bias of -27.5 V. The triode section serves as a local oscillator, featuring an amplification factor of 22 and a transconductance of 2,800 µmhos at a plate voltage of 100 V. With its internal connection between the triode grid and hexode Grid No. 3, the 14K7 offers an integrated, space-saving solution for superheterodyne receiver designs.
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.
2 physical sections, each with unique specifications.
Section 1
Conversion transconductance promoted.
Section 2
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
200 V
Screen voltage
85 V
Plate current
3 mA
Screen current
3 mA
Conversion transconductance
750 uS
Plate resistance
1000000 ohm
Grid-to-heater capacitance maximum
0.15 pF
Plate voltage
100 V
Plate current
10 mA
Transconductance
2800 uS
Amplification factor
22