Power - TV Vertical Output ·Pentode-Triode
11BM8
Miniature triode-pentode used for television vertical-deflection oscillator/amplifier service and AF voltage/power amplification. It combines a small-signal triode with a power pentode in one envelope.
- Sections
- 2
- Base
- 9EX
- Socket code
- B9A
- Base pins
- 9
- Nominal heater
- 10.7 V / 450 mA
Description
11BM8 — High-Mu Triode and Power Pentode
The 11BM8 is a miniature multi-unit vacuum tube containing a high-mu triode and a power pentode within a single envelope. It is designed for use in television receivers, where it serves as a vertical deflection oscillator or audio-frequency (AF) amplifier in its triode section, and as a vertical deflection amplifier or AF power amplifier in its pentode section. The 11BM8 is electrically identical to the 16A8/PCL82 and related to the 8B8, differing only in its heater characteristics.
Physical Construction, Heater, and Pinout
The 11BM8 is constructed in a T-6 1/2 miniature glass envelope with a 9-pin button base (E9-1). The physical dimensions of the tube are as follows:
| Physical Parameter | Value |
|---|---|
| Maximum Diameter | 0.875 inches |
| Maximum Seated Height | 2.812 inches |
| Maximum Overall Height | 3.062 inches |
| Outline Designation | 6-4 (also designated as 6G) |
Heater Operation
The heater is designed for series or parallel AC/DC operation with the following nominal ratings:
| Heater Parameter | Value |
|---|---|
| Heater Voltage | 10.7 V |
| Heater Current | 0.45 A (450 mA) |
| Maximum Heater-Cathode Voltage (Heater Negative with Respect to Cathode) | 200 V |
| Maximum Heater-Cathode Voltage (Heater Positive with Respect to Cathode) | 200 V |
Pinout and Basing
The tube utilizes the 9EX basing arrangement, which provides separate connections for the triode and pentode sections, with the exception of the shared heater. The pin connections, viewed from the bottom of the tube, are:
| Pin Number | Connection | Symbol |
|---|---|---|
| 1 | Grid No. 1 (Pentode) | G1p |
| 2 | Cathode, Grid No. 3, and Internal Shield (Pentode) | Kp, G3p, IS |
| 3 | Grid (Triode) | G1t |
| 4 | Heater | H |
| 5 | Heater | H |
| 6 | Plate (Pentode) | Pp |
| 7 | Grid No. 2 (Pentode) | G2p |
| 8 | Cathode (Triode) | Kt |
| 9 | Plate (Triode) | Pt |
Direct Interelectrode Capacitances
The direct interelectrode capacitances of the 11BM8 are measured without an external shield. These values define the capacitive coupling within each section and between the independent triode and pentode structures.
Triode Section Capacitances
| Parameter | Value |
|---|---|
| Grid to All Other Elements Except Plate | 2.7 pF |
| Plate to All Other Elements Except Grid | 4.3 pF |
| Plate to Grid | 4.2 pF |
| Grid to Heater (Maximum) | 0.02 pF |
Pentode Section Capacitances
| Parameter | Value |
|---|---|
| Grid No. 1 to All Other Elements Except Plate | 9.3 pF |
| Plate to All Other Elements Except Grid No. 1 | 8.0 pF |
| Plate to Grid No. 1 (Maximum) | 0.3 pF |
| Grid No. 1 to Heater (Maximum) | 0.3 pF |
Section-to-Section Coupling Capacitances
| Parameter | Value |
|---|---|
| Triode Plate to Pentode Grid No. 1 (Maximum) | 0.02 pF |
| Triode Grid to Pentode Plate (Maximum) | 0.02 pF |
| Triode Grid to Pentode Grid No. 1 (Maximum) | 0.025 pF |
| Triode Plate to Pentode Plate (Maximum) | 0.25 pF |
Maximum Ratings
The maximum ratings for the 11BM8 are established under the Design Center Rating System. These limits must be observed to ensure reliable operation and prevent premature tube failure.
Pentode Section Ratings
| Parameter | Maximum Value |
|---|---|
| Plate Voltage Without Plate Current | 550 V |
| Plate Voltage | 250 V |
| Peak Plate Voltage (Pulse duration ≤ 4% of one cycle, max 0.8 ms) | 2500 V |
| Peak Inverse Plate Voltage | 500 V |
| Plate Dissipation | 5 W |
| Peak Plate Dissipation | 7 W |
| Grid No. 2 Voltage Without Current | 550 V |
| Grid No. 2 Voltage | 250 V |
| Grid No. 2 Dissipation | 1.8 W |
| Peak Grid No. 2 Dissipation | 3.2 W |
| Cathode Current | 50 mA |
| Grid No. 1 Circuit Resistance (with Automatic Bias) | 2 M̤ |
| Grid No. 1 Circuit Resistance (with Fixed Bias) | 1 M̤ |
| Circuit Resistance Between Heater and Cathode | 20,000 ̩ |
Triode Section Ratings
| Parameter | Maximum Value |
|---|---|
| Plate Voltage Without Plate Current | 550 V |
| Plate Voltage | 250 V |
| Peak Plate Voltage (Pulse duration ≤ 4% of one cycle, max 0.8 ms) | 600 V |
| Plate Dissipation | 1 W |
| Cathode Current | 15 mA |
| Grid Circuit Resistance (with Automatic Bias) | 3 M̤ |
| Grid Circuit Resistance (with Fixed Bias) | 1 M̤ |
| Voltage Between Heater and Cathode | 200 V |
| Circuit Resistance Between Heater and Cathode | 20,000 ̩ |
| Grid Circuit Impedance (at 50 Hz) | 0.5 M̤ |
Typical Operating Characteristics
The triode and pentode sections of the 11BM8 can be operated under several typical Class A1 amplifier conditions.
Pentode Section Characteristics
The pentode section exhibits high transconductance and moderate plate resistance, making it suitable for power amplification and vertical deflection output stages. The table below outlines four typical operating points:
| Parameter | Point A | Point B | Point C | Point D |
|---|---|---|---|---|
| Plate Voltage | 100 V | 170 V | 200 V | 200 V |
| Grid No. 2 Voltage | 100 V | 170 V | 200 V | 200 V |
| Grid No. 1 Bias | -6.0 V | -11.5 V | -12.5 V | -16 V |
| Plate Current | 26 mA | 41 mA | 35 mA | 35 mA |
| Grid No. 2 Current | 5.0 mA | 8.0 mA | 6.5 mA | 7.0 mA |
| Transconductance | 6800 ̧mhos | 7500 ̧mhos | 6800 ̧mhos | 6400 ̧mhos |
| Plate Resistance (Approx.) | 15,000 ̩ | 16,000 ̩ | 20,500 ̩ | 20,000 ̩ |
| Amplification Factor (Grid No. 2 wrt Grid No. 1) | 10 | 9.5 | 9.5 | 9.5 |
Triode Section Characteristics
The high-mu triode section is optimized for voltage amplification or oscillator service. Under typical Class A1 conditions, its characteristics are:
| Parameter | Value |
|---|---|
| Plate Voltage | 100 V |
| Grid Voltage | 0 V |
| Plate Current | 3.5 mA |
| Transconductance | 2500 ̧mhos |
| Amplification Factor | 70 |
Technical Summary
The 11BM8 is a versatile, space-saving miniature 9-pin high-mu triode and power pentode designed primarily for television receiver applications. Featuring a 10.7 V, 450 mA heater, it integrates two distinct, high-performance electron systems in a single T-6 1/2 envelope. The triode section provides an amplification factor of 70 with a transconductance of 2500 ̧mhos at its typical operating point, while the pentode section delivers up to 5 W of plate dissipation and a transconductance of up to 7500 ̧mhos. By offering independent cathode connections and low inter-section coupling capacitances, the 11BM8 allows designers to implement vertical deflection, oscillator, and audio power amplification circuits with minimal component count and high electrical isolation between stages.
Socket description
Small-button Noval 9-contact
General specifications
Tube and section characteristics
Properties common to every published source and operating point.
Heater and base
- Base
- 9EX
- Socket code
- B9A
- Base pins
- 9
- Nominal heater voltage
- 10.7 V
- Nominal heater current
- 450 mA
- Parallel heater voltage
- -
- Parallel heater current
- -
- Series capable
- No
9EX - Terminal pinout
Electrical assignments shared by every tube using this base designation.
| Terminal | Section | Connection | Evidence |
|---|---|---|---|
| PIN1Base Pin | B | G1 — Control Grid Original chart label: 2G1; manufacturer verification pending | Unverified EIA Base Connections, printed page 132, 9EX |
| PIN2Base Pin | A | G3 — Suppressor GridGroup 9EX2 Original chart label: 1G3; manufacturer verification pending | Unverified EIA Base Connections, printed page 132, 9EX |
| PIN2Base Pin | A | K — CathodeGroup 9EX2 Original chart label: 1K; manufacturer verification pending | Unverified EIA Base Connections, printed page 132, 9EX |
| PIN3Base Pin | A | G1 — Control Grid Original chart label: 1G1; manufacturer verification pending | Unverified EIA Base Connections, printed page 132, 9EX |
| PIN4Base Pin | — | H — Heater Original chart label: H; manufacturer verification pending | Unverified EIA Base Connections, printed page 132, 9EX |
| PIN5Base Pin | — | H — Heater Original chart label: H; manufacturer verification pending | Unverified EIA Base Connections, printed page 132, 9EX |
| PIN6Base Pin | A | P — Plate (Anode) Original chart label: 1P; manufacturer verification pending | Unverified EIA Base Connections, printed page 132, 9EX |
| PIN7Base Pin | A | G2 — Screen Grid Original chart label: 1G2; manufacturer verification pending | Unverified EIA Base Connections, printed page 132, 9EX |
| PIN8Base Pin | B | K — Cathode Original chart label: 2K; manufacturer verification pending | Unverified EIA Base Connections, printed page 132, 9EX |
| PIN9Base Pin | B | P — Plate (Anode) Original chart label: 2P; manufacturer verification pending | Unverified EIA Base Connections, printed page 132, 9EX |
Section ratings
2 physical sections, each with unique specifications.
Section 1
Triode
- Transconductance
- 0.0025 S
- Amplification factor
- 70
- Max plate voltage
- 250 V
Vertical-deflection oscillator or AF voltage-amplifier section; ratings by explicit cross-reference to 16A8/PCL82.
Section 2
Pentode
- Plate resistance
- 20000 Ω
- Transconductance
- 0.0064 S
- Max plate voltage
- 250 V
- Max screen voltage
- 250 V
- Max plate dissipation
- 7 W
- Max screen dissipation
- 1.8 W
- Max cathode current
- 50 mA
Vertical-deflection or AF power-amplifier section; ratings by explicit cross-reference to 16A8/PCL82.
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.