Overview
The Eimac SK-400 Air-System tube socket is a precision-engineered RF socket designed for large-envelope tetrode and pentode vacuum tubes. This socket provides forced-air cooling to manage heat dissipation in high-power transmitting applications. The SK-400 is the recommended socket for the 4-400A tetrode and accommodates mechanically similar tubes, delivering low-inductance RF performance and efficient thermal management in demanding industrial and amateur radio environments.
Key Features
- Forced-air cooling system with integrated air-flow chimney path
- Low-inductance design for RF efficiency and minimal impedance distortion
- Accommodates 4-400A, 4-400C, 4-125A, 4PR400A, 4PR250C, 5-500A, and similar base tubes
- Ceramic construction with silver-plated contacts for corrosion resistance
- Accepts 2-inch OD tubing or fitting for air-blower connection
- Three-toe clamp or bolt-down chassis mounting options
Technical Specifications
- Socket Type: Air-System (chimney cooling)
- Recommended Tube: 4-400A tetrode
- Compatible Tubes: 4-400C, 4-125A, 4PR400A, 4PR250C, 5-500A (same base configuration)
- RF Contact Material: Silver-plated ceramic
- Cooling Method: Forced-air (requires external air blower)
- Air Inlet Fitting: 2-inch OD tubing or fitting connection
- Mounting Options: Chassis-mount with toe clamps or threaded fasteners (#10-32 machine screw holes)
- Operating Environment: RF/industrial transmitting applications
- Condition: New, no box
Typical Applications
- Amateur radio (ham radio) linear amplifiers and PA stages
- Induction heating systems
- RF plasma generators
- Industrial RF heaters and dielectric heating equipment
- Shortwave and HF transmitter platforms
- Test and measurement RF generators
Compatibility & Replacements
Compatible With
- Eimac 4-400A tetrode (primary application)
- Eimac 4-400C transmitting tube
- Eimac 4-125A linear amplifier tube
- Eimac 4PR400A (8188) pentode replacement
- Eimac 4PR250C tube variants
- Eimac 5-500A tetrode
- Other tubes with identical base pin configuration (3-500ZG, 3CX1200A7, and equivalent)
- Standard forced-air blower systems (requires 2-inch OD intake tubing)
Replaces / Drop-In Replacement For
- OEM Eimac SK-400 original equipment sockets
- Used or damaged SK-400 air-system sockets in existing RF amplifier platforms
- Verify tube base and flange dimensions before substituting for other socket models
Works With
- External forced-air cooling systems and blowers
- Industrial RF transmitter chassis and amateur radio amplifier designs
- High-voltage RF power supply modules (tube-plate supplies typically 2000–3000 V DC)
- Standard RF transmission-line and cavity-tank circuit topologies
- EIA and IEC industrial tube socket standards (vintage RF equipment)
