13FD7 — Dissimilar Double Triode Vacuum Tube
The 13FD7 is a miniature, dissimilar double triode vacuum tube designed for use in television receivers. It contains two electrically independent and distinct triode units within a single glass envelope: a high-mu triode (Unit No. 1) and a low-mu triode (Unit No. 2). The tube is primarily designed to serve as a combined vertical-deflection oscillator and vertical-deflection amplifier in television receivers operating under 525-line, 30-frame systems.
The 13FD7 is identical to the 6FD7 and 10FD7 except for its heater ratings and heater warm-up characteristics.
Construction, Physical Specifications, and Basing
The 13FD7 is constructed with a 9T-9 glass envelope (also designated as a T9 outline) and utilizes a button 9-pin base (E9-68). It requires a miniature 9-contact socket.
The physical dimensions of the tube are as follows:
- Maximum Diameter: 1.188 inches
- Maximum Seated Height: 2.620 inches
- Maximum Overall Height: 2.900 inches
The tube employs the 9HF basing diagram, which provides the following pin connections (viewed from the bottom of the base):
- Pin 1: Plate of Unit No. 2 (Low-Mu Amplifier)
- Pin 2: Grid of Unit No. 2 (Low-Mu Amplifier)
- Pin 3: Grid of Unit No. 2 (Low-Mu Amplifier)
- Pin 4: Heater
- Pin 5: Heater
- Pin 6: Plate of Unit No. 1 (High-Mu Oscillator)
- Pin 7: Grid of Unit No. 1 (High-Mu Oscillator)
- Pin 8: Cathode of Unit No. 1 (High-Mu Oscillator)
- Pin 9: Cathode of Unit No. 2 (Low-Mu Amplifier)
Heater Characteristics and Ratings
The heater of the 13FD7 is designed for series-string or parallel operation in television receivers. It has the following electrical specifications:
- Heater Voltage (AC/DC): 13.0 V
- Heater Current: 0.450 A (with a tolerance of 0.030 A)
- Average Heater Warm-up Time: 11 seconds
For comparison, the related 6FD7 operates at a heater voltage of 6.3 V and a current of 0.925 A, while the 10FD7 operates at 9.7 V and 0.600 A.
Heater-Cathode Voltage Limits
To prevent insulation breakdown, the voltage difference between the heater and the cathodes must be kept within the following design-maximum limits:
- Heater Negative with Respect to Cathode: 200 V maximum (total DC and peak)
- Heater Positive with Respect to Cathode: 100 V maximum DC, 200 V maximum (total DC and peak)
Electrical Characteristics and Class A1 Operation
The two triode sections of the 13FD7 have highly dissimilar electrical characteristics, optimized for their respective roles as oscillator and power amplifier.
Unit No. 1 (High-Mu Triode)
Unit No. 1 is characterized by high amplification factor and high plate resistance, making it suitable for voltage amplification and oscillation. Under typical Class A1 operating conditions, its characteristics are:
- Plate Voltage: 250 V
- Grid No. 1 Voltage: -3 V
- Amplification Factor: 64
- Plate Resistance (Approximate): 40,000 ̩
- Transconductance: 1,600 µmhos
- Plate Current: 1.4 to 1.5 mA
- Grid Voltage for Plate Current of 10 µA (Approximate): -5.5 V
Unit No. 2 (Low-Mu Triode)
Unit No. 2 is a low-impedance, high-current triode designed for power amplification. Its typical Class A1 characteristics are:
- Plate Voltage: 150 V
- Grid No. 1 Voltage: -17.5 V
- Amplification Factor: 6.0
- Plate Resistance (Approximate): 800 ̩
- Transconductance: 7,500 µmhos
- Plate Current: 40 mA
- Grid Voltage for Plate Current of 100 µA (Approximate): -40 V
- Transconductance at Plate Current of 1.0 mA: 500 µmhos
- Plate Current at Grid Voltage of -25 V (Approximate): 6 mA
An additional instantaneous operating point is specified for Unit No. 2 to illustrate its peak current capability:
- Plate Voltage: 60 V
- Grid No. 1 Voltage: 0 V
- Plate Current: 95 mA (measured using a recurrent waveform method to prevent exceeding the maximum ratings of the tube)
Vertical-Deflection Service Ratings
When operated as a combined vertical-deflection oscillator and vertical-deflection amplifier in a 525-line, 30-frame television system, the 13FD7 must be operated within the following Design-Maximum ratings:
Operating Conditions and Circuit Values
- Grid-Circuit Resistance: For both Unit No. 1 and Unit No. 2, the maximum grid-circuit resistance is 2.2 megohms under either grid-resistor-bias or cathode-bias (self-bias) operation.
- Pulse Duration Limit: For the peak ratings of Unit No. 2, the pulse duration must not exceed 15% of a vertical scanning cycle (equivalent to 2.5 milliseconds in a standard system).
- Grid Leak Bias Protection: In stages operating with grid leak bias, an adequate bias resistor or other suitable means is required to protect the tube from damage in the event that excitation is lost.
Interelectrode Capacitances
The direct interelectrode capacitances of the 13FD7 are measured without an external shield. The approximate values for each section are:
Technical Summary
The 13FD7 is a versatile, 9-pin miniature dissimilar double triode designed specifically for television vertical deflection circuits. It combines a high-mu triode (Unit No. 1, μ = 64) for oscillator service and a high-dissipation, low-impedance triode (Unit No. 2, r_p ≈ 800 ̩, P_d = 10 W) for vertical output amplification. Operating with a 13.0 V, 450 mA heater, it is well-suited for series-string heater chains. By integrating these two highly specialized triode units into a single compact envelope, the 13FD7 provides an efficient and space-saving solution for television receiver designs.
