10AF11 — Triple-Section Compactron Vacuum Tube

The 10AF11 is a multi-section vacuum tube designed in the Compactron envelope configuration. It integrates three distinct active electronic systems within a single glass envelope: a high-mu triode (designated Triode No. 1), a medium-mu triode (designated Triode No. 2), and a sharp-cutoff pentode. This combination of diverse tube structures is specifically tailored for television receiver applications, serving functions such as an automatic gain control (AGC) keyer, a sync separator, and a video amplifier.

Mechanical Construction, Base, and Physical Dimensions

The 10AF11 is built using the Compactron T-9 construction style, which provides a compact, multi-pin layout suitable for high-density chassis designs. The tube features a button 12-pin base, designated as the E12-70 type, and utilizes the 12DP basing arrangement.

The physical dimensions of the device are defined by the 9-58 outline specification:

• Maximum Diameter: 1.188 inches
• Maximum Seated Height: 2.250 inches
• Maximum Overall Height: 2.625 inches

Heater Specifications and Ratings

The heater of the 10AF11 is designed for series-string operation, featuring a controlled warm-up characteristic. The heater parameters and electrical insulation limits between the heater and the cathodes are as follows:

Heater-Cathode Voltage Limits

To prevent insulation breakdown and minimize noise, the potential difference between the heater and the individual cathodes must be kept within the following design-maximum limits:

• Heater Negative with Respect to Cathode: 200 Volts maximum (Total DC and Peak)
• Heater Positive with Respect to Cathode:
  • DC: 100 Volts maximum
  • Total DC and Peak: 200 Volts maximum

Electrical Characteristics and Typical Operating Points

Each of the three sections in the 10AF11 exhibits distinct electrical characteristics optimized for its respective role.

Triode No. 1 (High-Mu Triode)

Triode No. 1 is designed for high voltage gain. Under typical operating conditions, it exhibits the following characteristics:

• Plate Voltage: 200 V
• Grid Voltage: -2.0 V
• Amplification Factor (\u03bc): 68
• Plate Resistance (Approximate): 12,400 \u03a9
• Transconductance ($g_m$): 5,500 \u03bcmhos
• Plate Current: 7.0 mA
• Grid Voltage for Cutoff (at $I_b = 10\ \mu\text{A}$): -5.5 V (approximate)

Triode No. 2 (Medium-Mu Triode)

Triode No. 2 offers moderate amplification with lower plate resistance and higher current capability. Its typical operation is specified using cathode bias:

• Plate Voltage: 200 V
• Cathode-Bias Resistor: 220 \u03a9
• Amplification Factor (\u03bc): 41
• Plate Resistance (Approximate): 9,400 \u03a9
• Transconductance ($g_m$): 4,400 \u03bcmhos
• Plate Current: 9.2 mA
• Grid Voltage for Cutoff (at $I_b = 10\ \mu\text{A}$): -6.5 V (approximate)

Pentode Section (Sharp Cutoff)

The pentode section is characterized under two distinct operating conditions to illustrate its performance in different circuit configurations:

Design-Maximum Ratings

The design-maximum rating system defines the absolute limits within which the 10AF11 must be operated to ensure reliability and longevity. These ratings are specified individually for each section:

Triode No. 1

• Plate Voltage: 330 V maximum
• Positive DC Grid Voltage: 0 V maximum
• Plate Dissipation: 1.1 W maximum
• Maximum Grid Circuit Resistance:
  • Fixed Bias: 0.5 M\u03a9
  • Cathode Bias: 1.0 M\u03a9

Triode No. 2

• Plate Voltage: 330 V maximum
• Positive DC Grid Voltage: 0 V maximum
• Plate Dissipation: 2.0 W maximum
• Maximum Grid Circuit Resistance:
  • Fixed Bias: 0.5 M\u03a9
  • Cathode Bias: 1.0 M\u03a9

Pentode Section

• Plate Voltage: 330 V maximum
• Screen Supply Voltage: 330 V maximum
• Positive DC Grid No. 1 Voltage: 0 V maximum
• Plate Dissipation: 5.0 W maximum
• Screen Dissipation: 1.25 W maximum
• Maximum Grid No. 1 Circuit Resistance:
  • Fixed Bias: 0.25 M\u03a9
  • Cathode Bias: 1.0 M\u03a9

Direct Interelectrode Capacitances

The direct interelectrode capacitances of the 10AF11 are measured without an external shield. The input and output capacitance values are referenced to specific internal elements and the heater.

Section-Specific Capacitances

• Triode No. 1:
  • Grid to Plate: 1.9 pF
  • Input ($1Tg1$ to [$1Tk + 2Tk + Pk + Pg3 + h + IS$]): 3.0 pF
  • Output ($1Tp$ to [$1Tk + 2Tk + Pk + Pg3 + h + IS$]): 2.2 pF
• Triode No. 2:
  • Grid to Plate: 3.6 pF
  • Input ($2Tg1$ to [$2Tk + Pk + Pg3 + h + IS$]): 2.4 pF
  • Output ($2Tp$ to [$2Tk + Pk + Pg3 + h + IS$]): 3.8 pF
• Pentode Section:
  • Grid to Plate: 0.12 pF
  • Input ($Pg1$ to [$2Tk + Pk + Pg2 + Pg3 + h + IS$]): 10.0 pF
  • Output ($Pp$ to [$2Tk + Pk + Pg2 + Pg3 + h + IS$]): 4.5 pF

(Note: $1Tg1$, $2Tg1$, and $Pg1$ represent the control grids; $1Tp$, $2Tp$, and $Pp$ represent the plates; $1Tk$, $2Tk$, and $Pk$ represent the cathodes; $Pg2$ and $Pg3$ represent the pentode screen and suppressor grids; $h$ represents the heater; and $IS$ represents the internal shield.)

Inter-Section Coupling

To minimize crosstalk and unwanted feedback between the independent sections, the internal layout is designed for low capacitive coupling:

• Pentode Plate to Triode No. 2 Plate: 0.045 pF maximum
• Triode No. 1 Plate to Triode No. 2 Plate: 0.06 pF maximum

Technical Summary

The 10AF11 is a versatile Compactron vacuum tube containing three independent active sections: a high-mu triode, a medium-mu triode, and a sharp-cutoff pentode. Operating with a 9.8 V, 600 mA series heater, it is optimized for television receiver circuitry, specifically as an AGC keyer, sync separator, and video amplifier. By combining these three distinct structures into a single T-9 envelope with a 12-pin button base, the 10AF11 reduces component count and space requirements while maintaining high performance across all three stages.