Data set 01
1961 Tung Sol
Published operating points and test conditions from this source.
SECTION 1
Pentode
Other
Plate voltage
90 V
ClassA
Characteristic
Average diode current
0.7 mA
40VDC
Capacitance
Grid to plate
0.2 pF
Voltage Pentode or Tetrode (with diode) ·Diode-Pentode
1AF5
Source mismatch prevents a defensible functional classification: the supplied manufacturer page does not contain a printed 1AF5 entry, so neighboring tube data were not inferred.
Directly heatedCold cathodeCommon cathodeDissimilar
- Sections
- 2
- Base
- 6AU
- Socket code
- B7G
- Base pins
- 7
- Nominal heater
- 1.4 V / 25 mA
Description
1AF5 — Diode Sharp-Cutoff Pentode Vacuum Tube
A miniature, filament-type diode-pentode designed for use in portable radio receivers as a combined detector and audio-frequency (AF) amplifier.
Overview
The 1AF5 is a multi-unit miniature vacuum tube containing a single diode and a sharp-cutoff pentode within a single envelope. It was specifically engineered for portable, battery-operated receivers, where power conservation is critical. By reducing the filament power consumption by half compared to earlier tubes in similar service, the 1AF5 allowed for longer battery life in portable equipment.
The tube features a coated filament designed for low-current DC operation, though it can also be operated from AC sources. It is housed in a standard T-5 1/2 glass bulb with a miniature 7-pin button base.
Physical Construction and Filament Ratings
The 1AF5 is constructed in a miniature T-5 1/2 glass envelope with a miniature button 7-pin base. The tube can be mounted and operated in any position.
Physical Dimensions
- Maximum Diameter: 3/4 inch
- Maximum Overall Length: 2 1/8 inches
- Maximum Seated Height: 1 7/8 inches
- Outline Drawing: 5-2
Filament Characteristics
The tube utilizes a coated filament designed for highly efficient battery operation. For power-line applications, the filament voltage is centered at 1.4 V when operating from a normal 117 V line supply.
- Filament Voltage: 1.4 V (AC or DC)
- Filament Current: 25 mA (0.025 A)
- Filament Heating: Direct (coated filament)
Basing and Pinout Configurations
The 1AF5 is documented with three distinct pinout configurations across different specifications. Designers must verify the specific basing arrangement of the target component, as the pin assignments for the diode plate, pentode plate, and grids vary significantly.
Configuration A (Base Connection 6AU)
In this configuration, the pins are assigned as follows:
- Pin 1: Filament Negative (F-), Grid No. 3 (G3)
- Pin 2: Diode Plate (DP)
- Pin 3: Grid No. 1 (G1)
- Pin 4: Grid No. 2 (G2)
- Pin 5: Pentode Plate (P)
- Pin 6: No Connection (NC)
- Pin 7: Filament Positive (F+), Grid No. 3 (G3)
Configuration B (Basing 6AU-0-0)
An alternative standard assigns the pins as:
- Pin 1: Filament Negative (F-), Grid No. 3 (G3)
- Pin 2: No Connection (NC)
- Pin 3: Diode Plate (DP)
- Pin 4: Grid No. 2 (G2)
- Pin 5: Pentode Plate (P)
- Pin 6: Grid No. 1 (G1)
- Pin 7: Filament Positive (F+)
Configuration C (Bottom View 6AU)
A third documented variant lists the following layout:
- Pin 1: Filament Negative (F-), Grid No. 3 (G3)
- Pin 2: Diode Plate (Pd)
- Pin 3: Grid No. 2 (G2)
- Pin 4: Grid No. 1 (G1)
- Pin 5: No Connection (NC)
- Pin 6: Pentode Plate (P)
- Pin 7: Filament Positive (F+)
Electrical Ratings
The maximum ratings for the 1AF5 are established under the Design Center system (RMA Standard M8-210). These limits must not be exceeded under the worst-case operating conditions.
| Parameter | Maximum Rating |
|---|---|
| Plate Voltage (DC) | 110 V |
| Grid No. 2 (Screen) Voltage (DC) | 110 V |
| Positive Grid No. 1 Voltage (DC) | 0 V |
| Cathode Current | 2.5 mA |
| Diode Current (Continuous Operation) | 0.25 mA |
Typical Operating Conditions and Characteristics
The pentode section of the 1AF5 operates as a Class A (or Class A1) amplifier. Two primary operating points are documented, corresponding to typical portable battery supply voltages of 67.5 V and 90 V.
Pentode Section Operating Points
| Parameter | Operating Point 1 | Operating Point 2 |
|---|---|---|
| Plate Voltage | 67.5 V | 90 V |
| Grid No. 2 (Screen) Voltage | 67.5 V | 90 V |
| Grid No. 1 (Control Grid) Voltage | 0 V | 0 V |
| Plate Current | 0.7 mA | 1.1 mA |
| Grid No. 2 Current | 0.25 mA | 0.4 mA |
| Plate Resistance (rp) | 2.3 Megohms or 2.8 Megohms | 2.0 Megohms |
| Transconductance (gm) | 500 micromhos or 550 micromhos | 600 micromhos |
| Grid No. 1 Voltage (for gm = 10 micromhos) | -2.5 V | -3.5 V |
Note: At the 67.5 V operating point, different specifications list the plate resistance as either 2.3 Megohms or approximately 2.8 Megohms, with corresponding transconductance values of 500 or 550 micromhos.
Diode Section Characteristics
The diode unit is designed for signal detection. Under typical test conditions with 10 V DC applied, the average diode current is 0.7 mA.
Interelectrode Capacitances
The direct interelectrode capacitances of the 1AF5 are documented both with and without an external shield (specifically Shield #316 connected to Pin 1).
| Capacitance Parameter | Without Shield | With Shield | Unit |
|---|---|---|---|
| Grid No. 1 to Plate (G1 to P) | 0.2 (or 0.17) | 0.2 | uuf |
| Input: G1 to (F + G3 + G2) | 2.3 | 2.5 | uuf |
| Output: P to (F + G3 + G2) | 2.4 (or 4.8) | 4.3 | uuf |
| Diode Plate to Grid No. 1 (Pd to G1) Max. | 0.03 | 0.03 | uuf |
Technical Summary
The 1AF5 is a highly efficient, miniature diode-pentode vacuum tube designed for portable receiver applications. Operating with a filament current of only 25 mA at 1.4 V, it represents a significant reduction in power consumption compared to older tube designs. The sharp-cutoff pentode section provides high plate resistance (up to 2.8 Megohms) and moderate transconductance (up to 600 micromhos), making it an effective voltage amplifier, while the independent diode section serves as an AM detector. Designers must exercise caution regarding the physical pinout, as three distinct basing configurations exist in historical documentation.
Socket description
Miniature 7-contact
General specifications
Tube and section characteristics
Properties common to every published source and operating point.
Heater and base
- Base
- 6AU
- Socket code
- B7G
- Base pins
- 7
- Nominal heater voltage
- 1.4 V
- Nominal heater current
- 25 mA
- Parallel heater voltage
- -
- Parallel heater current
- -
- Series capable
- No
6AU - Terminal pinout
Electrical assignments shared by every tube using this base designation.
| Terminal | Section | Connection | Evidence |
|---|---|---|---|
| PIN11G3 | A | G3 — Suppressor GridGroup 6AU1 Original EIA label 1G3; independent manufacturer confirmation pending | Unverified EIA Base Connections, printed page 127, 6AU |
| PIN1F | — | F — FilamentGroup 6AU1 Original EIA label F; independent manufacturer confirmation pending | Unverified EIA Base Connections, printed page 127, 6AU |
| PIN32P | B | P — Plate (Anode) Original EIA label 2P; independent manufacturer confirmation pending | Unverified EIA Base Connections, printed page 127, 6AU |
| PIN41G2 | A | G2 — Screen Grid Original EIA label 1G2; independent manufacturer confirmation pending | Unverified EIA Base Connections, printed page 127, 6AU |
| PIN51P | A | P — Plate (Anode) Original EIA label 1P; independent manufacturer confirmation pending | Unverified EIA Base Connections, printed page 127, 6AU |
| PIN61G1 | A | G1 — Control Grid Original EIA label 1G1; independent manufacturer confirmation pending | Unverified EIA Base Connections, printed page 127, 6AU |
| PIN7F | — | F — Filament Original EIA label F; independent manufacturer confirmation pending | Unverified EIA Base Connections, printed page 127, 6AU |
Section ratings
2 physical sections, each with unique specifications.
Section 1
Pentode
X-ray radiationInterelectrode capacitances
- Plate resistance
- 2000000 Ω
- Transconductance
- 0.0006 S
- Max plate voltage
- 110 V
- Max screen voltage
- 110 V
- Max cathode current
- 2.5 mA
Source mismatch exception: approved PDF contains 1AF4 and 1AF6 rows but no printed 1AF5 row. Electrical values intentionally left unpopulated rather than inferred from a neighboring designation.
Section 2
Diode
X-ray radiationInterelectrode capacitances
No fixed ratings are recorded for this section.
Source-dependent data
Operating conditions by source
Each block preserves the test conditions and published values from one reference. Values from different sources are intentionally kept separate.