Eimac SK-400 Air-System Tube Socket – Forced-Air Cooling Vacuum Tube Socket

Eimac SK-400 Air-System Tube Socket

The Eimac SK-400 Air-System Tube Socket is engineered to provide efficient electrical connections and robust mechanical support for vacuum tubes, particularly the 4-400A tetrode. It is also compatible with other tubes sharing similar physical dimensions, such as the 4-250A, 4-125A, 3-500Z, and 3CX1200A7.

Design and Construction

Constructed with a cast aluminum body, the SK-400 serves multiple functions:

• Acts as an air duct, directing cooling air through the tube base and around the envelope.
• Supports electrical insulation for the terminals.
• Ensures a secure mechanical fit for the tube.

For optimal cooling, the SK-400 is typically used in conjunction with the SK-406 Air Chimney, which guides airflow over the tube envelope and plate seal. The SK-406 may be omitted only in specific cases where alternative cooling methods are implemented.

Installation and Mounting

Designed for under-chassis mounting, the SK-400 requires a three-inch diameter hole in the chassis deck. It is secured using four 10-32 machine screws that also hold small double clips to secure the SK-406 Air Chimney. The socket features self-aligning pin jacks to accommodate the tube’s base pins, ensuring reliable electrical connections.

Cooling Requirements

Adequate forced-air cooling is essential to maintain the base seals at temperatures below 200°C and the plate seal below 225°C. When using the SK-400 with the SK-406 Air Chimney, a minimum airflow of 14 cubic feet per minute at a static pressure of 0.25 inches of water is recommended to ensure proper cooling under all operating conditions.

Compatibility

The SK-400 is compatible with the following vacuum tubes:

• 4-400A
• 4-250A
• 4-125A
• 3-500Z
• 3CX1200A7

This compatibility makes the SK-400 a versatile choice for various applications requiring efficient tube cooling and support.