19HR6 — Semiremote-Cutoff Pentode
The 19HR6 is a miniature, semiremote-cutoff pentode designed primarily for use as an intermediate-frequency (IF) amplifier in FM receivers. It features a high transconductance and is constructed in a compact 7-pin miniature envelope.
Mechanical Specifications and Pinout
The 19HR6 is housed in a miniature T-5½ glass envelope with a button 7-pin base (E7-1 designation). It requires a standard miniature 7-contact socket. The physical dimensions of the tube are:
- Maximum Overall Height: 2.125 inches
- Maximum Seated Height: 1.875 inches
- Maximum Diameter: 0.750 inches
The tube utilizes the 7BK basing diagram. The pin connections, viewed from the bottom of the base, are as follows:
Heater and Heater-Cathode Ratings
The 19HR6 is designed for series-string or parallel heater circuits, featuring a controlled warm-up time. Its heater ratings and heater-cathode limits are:
- Heater Voltage (AC or DC): 18.9 V
- Heater Current: 0.150 A (150 mA) ± 0.010 A
- Average Heater Warm-up Time: 17 seconds
- Calculated Heater Power: 18.9 V × 0.150 A = 2.835 W (calculated from nominal voltage and current)
Heater-Cathode Voltage Limits (Design-Maximum Values)
- Heater Negative with Respect to Cathode (Total DC and Peak): 200 V max
- Heater Positive with Respect to Cathode (DC): 100 V max
- Heater Positive with Respect to Cathode (Total DC and Peak): 200 V max
- Peak Heater-Cathode Voltage: 200 V max
- Average Heater-Cathode Voltage: 100 V max
Direct Interelectrode Capacitances
The capacitances of the 19HR6 are specified for an unshielded tube:
- Grid No. 1 to Plate (Maximum): 0.006 pF
- Grid No. 1 to Cathode, Grid No. 3, Internal Shield, Grid No. 2, and Heater: 8.8 pF
- Plate to Cathode, Grid No. 3, Internal Shield, Grid No. 2, and Heater: 5.2 pF
Maximum Ratings (Design-Maximum System)
The following maximum ratings are established for Class A1 amplifier service:
- Plate Supply Voltage: 300 V max
- Grid No. 3 (Suppressor-Grid) Positive Voltage: 0 V max (Grid No. 3 should be connected to the cathode at the socket)
- Grid No. 2 (Screen-Grid) Supply Voltage: 300 V max
- Grid No. 2 Voltage: Dependent on operating conditions (subject to rating curves)
- Grid No. 1 (Control-Grid) Positive-Bias Voltage: 0 V max
- Grid No. 1 (Control-Grid) Negative-Bias Voltage: 50 V max
- Plate Dissipation: 3 W max
- Grid No. 2 Input:
- For Grid No. 2 voltages up to 150 V: 1 W max
- For Grid No. 2 voltages between 150 V and 300 V: Subject to rating curves
Maximum Circuit Values
- Grid No. 1 Circuit Resistance (Fixed-bias): 0.5 MΩ max
- Grid No. 1 Circuit Resistance (Cathode-bias): 1 MΩ max
Typical Characteristics and Class A1 Operation
Under typical operating conditions as a Class A1 amplifier, the 19HR6 exhibits high transconductance and high plate resistance. The typical operating parameters are:
- Plate Supply Voltage: 200 V
- Grid No. 3 (Suppressor-Grid): Connected to cathode at the socket
- Grid No. 2 Supply Voltage: 115 V
- Grid No. 1 Supply Voltage: 0 V
- Cathode-Bias Resistor: 68 Ω
- Plate Resistance (Approximate): 0.5 MΩ
- Transconductance: 8500 µmhos
- Plate Current: 13.2 mA
- Grid No. 2 Current: 4.3 mA
- Grid No. 1 Voltage for Transconductance of 60 µmhos (Approximate): -15 V
Electrical Behavior and Curve Observations
The 19HR6 exhibits typical pentode characteristics. When plate current and Grid No. 2 current are plotted against plate voltage up to 300 V (with Grid No. 2 held at 115 V and Grid No. 3 connected to the cathode), the following behaviors are observed:
- Pentode Knee: A distinct pentode knee is present below 50 V plate voltage, where plate current rises rapidly before flattening into a relatively constant region.
- Control Grid Bias: The Grid No. 1 bias curves range from 0 V to -8 V.
- Semiremote-Cutoff Characteristic: The tube's semiremote-cutoff design is demonstrated by its transconductance behavior. At a typical bias point, the transconductance is 8500 µmhos, but it is reduced to approximately 60 µmhos when the Grid No. 1 bias is increased to -15 V. This allows the tube to handle a wide range of signal levels without excessive distortion, making it highly suitable for automatic volume control (AVC) or automatic gain control (AGC) circuits in IF stages.
Related Designations
The 19HR6 is identical to the 6HR6 except for its heater characteristics and ratings. The 6HR6 is designed for a different heater supply, whereas the 19HR6 is optimized for series-string heater chains requiring a 0.150 A current and an 18.9 V drop.
Technical Summary
The 19HR6 is a 7-pin miniature semiremote-cutoff pentode designed for IF-amplifier service in FM receivers. It features an 18.9 V, 150 mA heater with a controlled 17-second warm-up time. Operating at a typical plate supply of 200 V and a screen supply of 115 V, it provides a high transconductance of 8500 µmhos and a plate resistance of approximately 0.5 MΩ. Its semiremote-cutoff characteristic allows for effective gain control, while its low grid-to-plate capacitance of 0.006 pF ensures stable high-frequency amplification.
