1. Introduction and History
The CV4055, also known commercially as the 6CH6, is a British military specification vacuum tube manufactured by Brimar (British Radio Valve Manufacturers Association) and STC (Standard Telephones and Cables) at their Rochester facility. The CV designation (Common Valve) was part of the British military nomenclature system for vacuum tubes used in defense equipment during and after World War II.
Developed in the 1950s, the CV4055 was designed to meet rigorous military standards for reliability and performance under extreme conditions. The tube was primarily manufactured for use in British military communications equipment and radar systems, where consistent performance and durability were critical requirements.
Brimar, a significant player in the British valve industry, produced these tubes with high-quality control standards. The production at STC Rochester facility ensured that these valves met the exacting specifications required for military applications. The "NOS" (New Old Stock) designation indicates unused, factory-original tubes from the original production runs.
2. Technical Specifications and Design
The CV4055/6CH6 is a beam power tetrode vacuum tube with the following specifications:
- Heater Voltage: 6.3V
- Heater Current: Approximately 0.75A
- Plate (Anode) Voltage: Maximum 300V
- Screen Grid Voltage: Maximum 300V
- Plate Dissipation: Approximately 10W
- Transconductance: Around 11,000 μmhos (11 mA/V)
- Base: 9-pin miniature (B9A)
The tube features a beam-forming design that enhances efficiency by using beam-forming plates to direct the electron flow from the cathode to the anode. This construction results in improved power handling capabilities and reduced screen current compared to conventional tetrodes.
The internal structure includes:
- Indirectly heated oxide-coated cathode
- Control grid (G1) for signal input
- Screen grid (G2) for electron acceleration
- Beam-forming plates (connected internally to the cathode)
- Anode (plate) for collecting the electron flow
The tube is enclosed in a glass envelope with a 9-pin base arrangement, making it compact compared to earlier power tube designs. The military specification version (CV4055) typically includes additional ruggedization features to withstand vibration, shock, and temperature extremes encountered in military environments.
3. Applications and Usage
The CV4055/6CH6 found widespread use in various applications, including:
Military Applications:
- RF Power Amplifiers: Used in military radio transmitters and communication equipment
- Radar Systems: Employed in pulse modulators and amplifier stages
- Signal Processing: Used in various military electronic systems requiring reliable amplification
Civilian Applications:
- Video Amplifiers: The 6CH6 commercial equivalent was commonly used in television video output stages
- RF Amplifiers: Used in radio frequency applications requiring moderate power
- Audio Power Amplifiers: Sometimes employed in audio equipment, although not as common as dedicated audio tubes
In circuit design, the CV4055/6CH6 is typically operated with the following considerations:
- Proper heater voltage regulation to ensure consistent performance
- Adequate ventilation due to its power dissipation characteristics
- Appropriate screen grid voltage regulation to prevent excessive current
- Careful attention to input circuit design to prevent oscillation in RF applications
4. Equivalent or Substitute Types
The CV4055 has several equivalent or substitute types that can be used in most applications:
- 6CH6: The commercial equivalent to the CV4055, electrically identical but without the military specifications
- 6AG7: Can serve as a substitute in some applications, though with slightly different characteristics
- 6CL6: Similar beam power tetrode that can replace the CV4055 in many circuits with minor adjustments
- CV5060: Another British military valve that can substitute in certain applications
- EL83: European equivalent that can be used in some applications with appropriate socket adaptation
When substituting tubes, it's important to consider not only the electrical characteristics but also the physical dimensions and pin configurations. While the above tubes can often serve as replacements, circuit modifications may be necessary to accommodate differences in operating parameters.
5. Notable Characteristics
The CV4055/6CH6 has several notable characteristics that distinguish it from other vacuum tubes of its era:
- Reliability: As a military specification valve, the CV4055 was built to higher reliability standards than commercial equivalents, with rigorous testing and selection processes
- Ruggedness: Designed to withstand mechanical shock and vibration encountered in military environments
- Extended Temperature Range: Capable of operating reliably across a wider temperature range than commercial tubes
- Low Microphonics: The construction techniques used in military tubes often resulted in lower sensitivity to mechanical vibration (microphonics)
- Consistent Performance: Military tubes typically showed less variation in characteristics between specimens than commercial versions
The Brimar/STC manufactured CV4055 tubes are particularly valued by collectors and enthusiasts for their build quality. The Rochester facility was known for producing high-quality valves with excellent consistency and durability.
For vintage equipment restoration, the CV4055 NOS tubes offer authentic period-correct components that maintain the original design characteristics of the equipment. This makes them particularly valuable for museum-quality restorations of military radio and radar equipment from the 1950s and 1960s.
Modern audio enthusiasts sometimes use these tubes in custom amplifier designs, valuing them for their robust construction and reliable performance characteristics, though they were not originally designed specifically for high-fidelity audio applications.
Conclusion
The CV4055/6CH6 represents an important part of British vacuum tube technology history, embodying the high standards required for military electronics during the mid-20th century. While primarily designed for military applications, these tubes found their way into various civilian uses and continue to be sought after by collectors, restorers, and enthusiasts. The Brimar/STC Rochester production of these tubes ensures a level of quality that remains impressive even by today's standards.
