Voltage - Triode (with diode, heptode or hexode) ·Diode-Diode-Triode
Miniature double-diode triode for detector and amplifier service. Two diodes provide signal detection or related rectification while the lower-mu triode supplies comparatively strong current capability.
The 12BU6 is a miniature, double-diode triode vacuum tube designed for use as a combined low-mu triode voltage amplifier and double diode detector. Constructed in a compact 7-pin miniature envelope, it is engineered to deliver high rectification efficiency at low signal levels while providing a triode section capable of handling large output signals with minimal distortion.
The 12BU6 features a T-5 1/2 glass bulb and utilizes a 7-pin miniature button base (E7-1 designation, with a 7BT or 7BT-0-2 basing arrangement). The tube incorporates a coated, unipotential cathode.
The physical dimensions of the device are characterized by the following maximum limits:
The tube is designed to operate in any mounting position. To prevent unwanted interaction between the high-frequency diode signals and the sensitive triode section, the 12BU6 includes internal diode shielding. This shielding reduces undesirable audio coupling between the diodes and the triode.
The 12BU6 is equipped with a heater designed for series or parallel operation with AC or DC power.
| Heater Parameter | Value |
|---|---|
| Nominal Heater Voltage | 12.6 V |
| Nominal Heater Current | 150 mA |
Viewed from the bottom of the miniature button 7-pin base, the electrical connections are assigned as follows:
The capacitances of the internal elements are specified both with and without an external shield (specifically, an RMA shield #316 connected directly to Pin 2):
| Capacitance Parameter | Without Shield | With Shield |
|---|---|---|
| Diode #2 Input: Plate #2 to (Heater + Cathode + Internal Shield) | 1.0 µµF | 1.0 µµF |
| Diode #1 Input: Plate #1 to (Heater + Cathode + Internal Shield) | 1.0 µµF | 1.0 µµF |
| Diode #1 Plate to Control Grid (Maximum) | 0.013 µµF | 0.01 µµF |
The maximum ratings for the 12BU6 are established under the Design Center system (interpreted according to RMA Standard MB-210):
| Rating Parameter | Limit |
|---|---|
| Maximum Plate Voltage (DC) | 300 V |
| Maximum Positive Grid Voltage (DC) | 0 V |
| Maximum Heater-Cathode Voltage | 90 V |
| Maximum Continuous Diode Current (Each Plate) | 1.0 mA |
The triode section of the 12BU6 can be operated under different plate voltage conditions. The following table outlines typical operating parameters for two distinct plate voltages:
| Parameter | Low-Voltage Condition | High-Voltage Condition |
|---|---|---|
| Plate Voltage | 100 V | 250 V |
| Grid Voltage | -3 V | -9 V |
| Self-Bias Resistor | 770 Ω | 950 Ω |
| Plate Current | 3.9 mA | 9.5 mA |
| Plate Resistance | 11,000 Ω | 8,500 Ω |
| Transconductance | 1,500 µmhos | 1,900 µmhos |
| Amplification Factor | 16.5 | 16 |
| Load Resistance | — | 10,000 Ω |
| Total Harmonic Distortion | — | 6.5% |
| Power Output | — | 300 mW |
The two diode units are designed with high perveance to ensure efficient detection. When a DC potential of 10 volts is applied to each diode plate, the current characteristics are:
The 12BU6 is primarily employed in receiver circuits where it performs the dual roles of AM detection (or automatic volume control rectification) and audio voltage amplification.
The low amplification factor (approximately 16) of the triode unit is a deliberate design choice. It allows the stage to handle large input signal swings and deliver substantial output voltages with low distortion. At a plate voltage of 250 V and a load resistance of 10,000 Ω, the triode can deliver 300 mW of power with only 6.5% total harmonic distortion.
Analysis of the triode characteristic curves shows that:
The high-perveance diodes provide highly efficient rectification even when operating with weak input signals. Performance curves for each diode unit demonstrate the relationship between the rectified microamperes and the DC voltage developed across various load resistors (ranging from 0.1 Megohm to 2.0 Megohms) under RMS signal inputs up to 30 V. The internal shield connected to Pin 2 ensures that these high-frequency rectified signals do not couple into the triode grid circuit, preserving audio signal purity.
The 12BU6 is closely associated with the 6BU6 designation. The two types share identical physical construction, electrode configurations, and typical operating characteristics, differing primarily in their heater ratings (the 6BU6 utilizing a 6.3 V heater supply).
The 12BU6 is a versatile, 7-pin miniature double-diode triode featuring a 12.6 V, 150 mA heater and a unipotential cathode. It combines a low-mu (\mu \approx 16) triode voltage amplifier with two high-perveance diode detectors in a single T-5 1/2 glass envelope. With built-in diode shielding to minimize internal capacitive coupling, a maximum plate voltage rating of 300 V, and the ability to operate in any mounting position, the 12BU6 serves as an efficient and compact solution for detection and audio pre-amplification in electronic receiver designs.
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
Published source values promoted where applicable.
Section 2
Published source values promoted where applicable.
Section 3
Published source values promoted where applicable.
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.
Heater voltage
12.6 V
Nominal
Heater current
300 mA
Nominal
Plate voltage
300 V
Typical operating conditions
Plate current
3.99.5 mA
Typical operating conditions