1610 — Crystal-Oscillator Power Pentode

The 1610 is a filament-type power pentode designed primarily for use as a crystal oscillator and radio-frequency (RF) power amplifier. It features a coated filament and is capable of operating at maximum ratings at frequencies up to 20 megacycles, and with reduced input at frequencies up to 110 megacycles. In historical catalogs, the 1610 is classified as a discontinued type listed for reference.

Filament, Mechanical, and Pin Connections

The 1610 is constructed with a coated filament and housed in an ST 16 glass bulb with a medium 5-pin base. It requires a small five-contact socket for installation. To ensure proper operation, the socket should preferably be installed to hold the tube in a vertical position, mounted either base up or base down.

The filament is designed for either alternating current (AC) or direct current (DC) operation. The filament and base pin connections, viewed from the top of the socket, are as follows:

• Pin 1: Filament (+)
• Pin 2: Plate
• Pin 3: Grid (Grid No.1)
• Pin 4: Screen (Grid No.2)
• Pin 5: Filament (-)

Electrical Characteristics and Capacitances

The 1610 exhibits a transconductance of 2500 micromhos (µmhos) when measured at a plate current of 31 milliamperes. The direct interelectrode capacitances of the tube are defined with respect to the filament mid-tap, grid No.3 (suppressor grid), and grid No.2 (screen grid) as follows:

Maximum Ratings (Continuous Commercial Service)

For RF power amplifier and oscillator service under Class C Telegraphy (key-down conditions per tube without amplitude modulation), the maximum Continuous Commercial Service (CCS) ratings are:

When operated at these maximum CCS ratings, the plate of the 1610 shows no color. Under modulated conditions, essentially negative amplitude modulation may be used, provided that the positive peak of the audio-frequency envelope does not exceed 115% of the carrier conditions.

Typical Class C Operating Conditions

The 1610 can be operated under typical Class C Telegraphy conditions at two distinct plate voltage levels. The typical operating parameters for these points are outlined below:

Application and Circuit Design

When utilized as a crystal-controlled oscillator, the 1610 requires specific circuit values to ensure stable and reliable operation:

• Grid-Leak Resistance: The grid circuit should be operated with a grid-leak resistance of approximately 30,000 ohms, with a power rating of at least 1 watt.
• Screen Voltage Supply: When the tube is configured as an oscillator, the screen voltage should not be left floating; it must be obtained either from a fixed voltage supply or from a potentiometer connected across the main plate-voltage supply.
• High-Frequency Limits: While the tube can be operated at its maximum ratings up to 20 megacycles, operation at higher frequencies up to 110 megacycles is permissible only with reduced input.

Technical Summary

The 1610 is a specialized 2.5 V filament-type power pentode designed for crystal oscillator and RF power amplifier applications. It features a robust 6-watt maximum plate dissipation rating under Class C service, a transconductance of 2500 µmhos, and low grid-to-plate capacitance (1.2 µµF) suitable for high-frequency stability. Housed in an ST 16 bulb with a medium 5-pin base, it provides reliable performance up to 20 megacycles at full ratings, and up to 110 megacycles with reduced input, making it a highly capable component for transmitter and oscillator designs within its specified operating envelope.