11MS8 — High-Mu Triode and Beam Power Tube

The 11MS8 is a multi-unit miniature vacuum tube containing a high-mu triode and a beam power tube in a single envelope. It is designed primarily for use in combined vertical-deflection-oscillator and vertical-deflection-amplifier applications in black-and-white television receivers.

Heater and Physical Specifications

The 11MS8 is constructed as a miniature tube requiring a standard miniature 9-contact socket. It features a controlled heater warm-up time, making it suitable for series-string heater arrangements.

Pinout and Electrode Connections

The 11MS8 uses the 9LY basing arrangement. The connections, viewed from the bottom of the tube, are assigned as follows:

• Pin 1: Grid (Triode Unit) — GT
• Pin 2: Plate (Triode Unit) — PT
• Pin 3: Cathode (Triode Unit) — KT
• Pin 4: Heater — H
• Pin 5: Heater — H
• Pin 6: Grid No. 1 / Control Grid (Beam Power Unit) — G1P
• Pin 7: Cathode and Grid No. 3 / Beam Plates (Beam Power Unit) — KP, G3P
• Pin 8: Grid No. 2 / Screen Grid (Beam Power Unit) — G2P
• Pin 9: Plate (Beam Power Unit) — PP

Class A1 Amplifier Characteristics

The triode and beam power units can be operated as Class A1 amplifiers. The triode unit is characterized by a high amplification factor, while the beam power unit provides higher current capability and power output.

Triode Unit Characteristics

The triode unit has two documented operating points under Class A1 conditions:

Beam Power Unit Characteristics

The beam power unit is characterized under the following Class A1 operating point:

• Plate Voltage: 120 V
• Grid-No. 2 (Screen-Grid) Voltage: 110 V
• Grid-No. 1 (Control-Grid) Voltage: -10 V
• Plate Current: 50 mA
• Grid-No. 2 Current: 3 mA
• Transconductance: 8500 µmhos
• Amplification Factor (with Grid-No. 2 connected to plate at socket): 5.8
• Plate Resistance (Approximate): 13,000 Ω

Vertical-Deflection Service and Maximum Ratings

For operation in a television receiver utilizing a 525-line, 30-frame system, the 11MS8 is rated under the Design-Maximum system. These ratings must not be exceeded under the worst-case operating conditions.

Design-Maximum Ratings

* Note on Peak Positive Pulse Plate Voltage: The pulse duration must not exceed 15% of a vertical scanning cycle, which corresponds to a maximum duration of 2.5 milliseconds.

Maximum Circuit Values

The maximum allowable grid-circuit resistance depends on the biasing method and the specific unit:

• Triode Unit Grid-No. 1 Circuit Resistance:
  • For fixed-bias operation: 1 megohm (maximum)
  • For cathode-bias operation: 3.3 megohms (maximum)
• Beam Power Unit Grid-No. 1 Circuit Resistance:
  • Maximum resistance: 2 megohms

Technical Summary

The 11MS8 is a versatile, space-saving television tube combining a high-mu triode and a beam power unit in a single 9-pin miniature envelope. With a heater rating of 11.6 V / 0.45 A and a controlled 11-second warm-up time, it is optimized for series-string television designs. The triode unit, featuring an amplification factor of up to 63, is well-suited for vertical-deflection oscillator service, while the beam power unit, capable of handling up to 2000 V peak positive plate pulses and 6 W of plate dissipation, is designed to drive the vertical-deflection amplifier stage.