Voltage - Triode (with diode, heptode or hexode) ·Diode-Diode-Triode
Double-diode high-mu triode for detector, AVC, and voltage-amplifier service in series-heater receivers. The paired diodes provide signal and control-voltage rectification while the triode supplies substantial gain for the recovered audio signal.
A miniature multi-unit vacuum tube containing a high-mu triode and two independent diodes, designed for detector and amplifier applications in AC/DC radio receivers.
The 18FY6 is a miniature, multi-unit vacuum tube featuring a high-mu triode and two diodes within a single T-5½ glass envelope. It is designed primarily for detector-amplifier service in AC/DC-type radio receivers. The tube utilizes a miniature button 7-pin base (7BT) and is equipped with a coated unipotential cathode. Its physical design allows it to be mounted and operated in any position.
The 18FY6 is designed for series-string or parallel heater circuits, requiring a nominal heater supply of 18 volts (AC or DC) at a current of 0.10 amperes (100 mA).
The design-maximum ratings for the tube, interpreted according to the Design-Maximum System, establish the limits within which the device must be operated to ensure reliability:
| Parameter | Rating |
|---|---|
| Heater Voltage | 18 V |
| Maximum Plate Voltage | 150 V |
| Maximum Plate Dissipation | 0.5 W |
| Maximum Positive Grid Voltage | 0 V |
| Maximum Diode Plate Current (Each Diode) | 1.0 mA |
| Maximum Heater-Cathode Voltage | 100 V |
The 18FY6 uses a miniature button 7-pin base (7BT). Published specifications describe two distinct pinout configurations (viewed from the bottom of the base). Designers must verify the specific pinout of the target device:
In this layout, the heater connections are located on adjacent pins near the center of the sequence:
In this alternative layout, the heater pins are shifted, and the cathode and diode connections are rearranged:
In both configurations, Pin 1 remains the control grid of the triode section, and Pin 7 remains the triode plate.
The direct interelectrode capacitances of the 18FY6 vary depending on whether an external shield is employed. The values below are measured with and without Shield #316 (connected to Pin #2):
The significant reduction in output capacitance when operating without a shield (from 2.0 μμF down to 0.22 μμF) highlights the impact of external shielding on the RF/IF characteristics of the triode plate circuit.
For Class A1 amplifier service, the typical operating parameters and characteristics of the triode section are as follows:
The high amplification factor of 100 makes the triode section highly suitable for high-gain voltage preamplification.
The two diode sections are intended for detection and automatic volume control (AVC) or automatic gain control (AGC) functions. Under a specific test condition with 10 volts applied, each diode exhibits an average diode current of 2.0 mA. This is a test condition only and does not represent a continuous operating rating; the maximum continuous diode plate current is limited to 1.0 mA per diode.
The 18FY6 is a versatile miniature high-mu triode double diode housed in a T-5½ glass envelope with a 7-pin miniature button base (7BT). Operating with an 18 V, 0.10 A heater, it combines a high-gain triode (amplification factor of 100) with two independent detector diodes. The triode section is optimized for Class A1 voltage amplification, featuring a transconductance of 1,300 μmhos and a plate resistance of 77,000 Ω at a typical plate voltage of 100 V. With its dual-diode structure and high-mu triode, the 18FY6 serves as a compact, single-tube solution for signal detection, AVC/AGC generation, and audio preamplification in AC/DC radio receivers.
Miniature 7-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.
Detector diode section; maximum continuous plate current 1 mA.
Section 2
No fixed ratings are recorded for this section.
Second detector diode section; maximum continuous plate current 1 mA.
Section 3
High-mu triode section.
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.
Average Diode Current
2 mA
EachDiode;10VApplied
Plate Voltage
100 V
ClassA
Plate Current
0.6 mA
ClassA
Data set 02
Published operating points and test conditions from this source.
Maximum diode plate current
1 mA
WholeTube
Average diode current with 10 V applied
2 mA
Section2
Maximum diode plate current
1 mA
WholeTube
Average diode current with 10 V applied
2 mA
Section3
Triode grid-to-plate capacitance
1.8 pF
WholeTube
Triode input capacitance
2.4 pF
WholeTube
Grid-to-diode plate capacitance maximum
0.2 pF
WholeTube
Maximum triode plate voltage
150 V
WholeTube
Maximum triode plate dissipation
0.5 W
WholeTube
Triode grid voltage
-1 V
TypicalOperation
Triode plate current
0.8 mA
TypicalOperation
Triode transconductance
1300 µS
TypicalOperation
Triode plate resistance
77000 ohm
TypicalOperation
Triode amplification factor
100
TypicalOperation