1633 — Medium-Mu Twin Triode Vacuum Tube

The 1633 is an indirectly heated, medium-mu twin triode vacuum tube designed for Class A amplifier service. It features two independent triode sections enclosed within a single envelope, sharing a common heater but having separate cathode, grid, and plate connections. The tube is characterized by its 25.0 V heater, octal base configuration, and moderate amplification factor, making it suitable for various voltage amplification and driver applications where a dual-triode configuration is advantageous.

Construction, Heater, and Base Connections

The 1633 is constructed with two electrically independent triode units. Each section has its own separate cathode, control grid, and plate, allowing them to be operated in independent circuits or in cascade. The cathodes are indirectly heated, coated unipotential types.

The heater is designed for series-string or high-voltage heater circuits, requiring a nominal voltage of 25.0 V and a current of 0.15 A. This corresponds to a calculated heater power consumption of:

$\text{Heater Power} = 25.0\text{ V} \times 0.15\text{ A} = 3.75\text{ W}$

The tube utilizes an 8BD octal base connection scheme and is housed in an envelope designated by outline drawing 9-11. The 8BD basing arrangement provides symmetrical pin assignments for the two triode sections, viewed from the bottom of the base:

This symmetrical layout places the heater connections on the outer pins (Pins 1 and 8) adjacent to the locating key, while the active electrodes for Triode 1 are on Pins 5, 6, and 7, and those for Triode 2 are on Pins 2, 3, and 4.

Electrical Characteristics and Operating Points

The 1633 is rated for a maximum plate voltage of 300 V. Under typical Class A amplifier operating conditions, each individual triode section exhibits the following electrical characteristics:

The relationship between the amplification factor ($\mu$), transconductance ($g_m$), and plate resistance ($r_p$) can be verified mathematically using the standard triode formula:

$\mu \approx g_m \times r_p$

Using the typical values provided:

$0.0026\text{ S} \times 6,900\ \Omega = 17.94$

This calculated value closely aligns with the published nominal amplification factor of 18. The moderate plate resistance of approximately 6,900 $\Omega$ combined with a transconductance of 2,600 $\mu$mhos allows each section to deliver clean voltage amplification with reasonable drive capability.

Technical Summary

The 1633 is an octal-based, indirectly heated medium-mu twin triode featuring a 25.0 V, 0.15 A heater and a maximum plate voltage rating of 300 V. With its independent triode sections, the tube provides versatile performance in Class A amplifier service. At a typical operating point of 250 V on the plate and a -8 V grid bias, each section draws 11.5 mA of plate current, providing an amplification factor of 18, a transconductance of 2,600 $\mu$mhos, and an approximate plate resistance of 6,900 $\Omega$. Its symmetrical 8BD base connection simplifies circuit layout for dual-channel or cascaded amplifier designs.