Introduction and History
The CV2136 is a British military designation for the 6BW6 beam tetrode vacuum tube, manufactured by Brimar (British Radio Mfg.) among other manufacturers during the mid-20th century. Developed in the post-World War II era, this tube emerged during a period when vacuum tube technology was reaching its peak of refinement before the transition to solid-state electronics.
The CV designation (Common Valve) was part of the British military standardization system for electronic components. The CV2136 was primarily designed for audio applications, reflecting the need for reliable audio amplification in both military and civilian equipment during the 1950s and 1960s.
Brimar, a respected British manufacturer, produced these tubes to high-quality standards, which explains why New Old Stock (NOS) examples are still sought after by audio enthusiasts and vintage equipment restorers today.
Technical Specifications and Design
The CV2136/6BW6 is a beam power tetrode with the following specifications:
- Heater (Filament): 6.3V at 1.2A
- Envelope: Glass, miniature 9-pin base (B9A)
- Maximum Plate Voltage: 300V
- Maximum Screen Voltage: 300V
- Maximum Plate Dissipation: 12W
- Maximum Screen Dissipation: 2.5W
- Transconductance: Approximately 10 mA/V
- Amplification Factor: Around 8
The tube features beam-forming plates that direct the electron flow from the cathode to the plate, reducing screen current and improving efficiency. This design allows for higher power output with lower distortion compared to conventional tetrodes.
The internal construction includes a cathode, control grid, screen grid, beam-forming plates, and plate (anode). The 9-pin miniature base layout follows the standard configuration for similar power tubes of the era.
Applications and Usage
The CV2136/6BW6 found widespread application in various electronic equipment:
Audio Applications
- Audio Power Amplifiers: Commonly used in the output stages of radio and television receivers, as well as dedicated audio amplifiers
- Push-Pull Configurations: Often employed in pairs for higher power output in hi-fi equipment
- Single-Ended Amplifiers: Used in simpler designs where moderate power was required
Military and Industrial Applications
- Military Communications: Used in various signal amplification roles
- Test Equipment: Employed in oscilloscopes and other measurement devices
- Industrial Control Systems: Utilized in various control circuits where reliability was paramount
In typical audio applications, the CV2136 would be biased to operate in class AB for a good balance of efficiency and low distortion. When properly configured, it could deliver approximately 5-8 watts of audio power in single-ended configurations, or 10-15 watts in push-pull pairs.
Equivalent or Substitute Types
The CV2136 has several direct equivalents and potential substitutes:
Direct Equivalents
- 6BW6: The commercial designation for the same tube
- N727: Another British designation sometimes used
Close Substitutes
- 6V6GT/6V6: Similar characteristics but with some differences in operating parameters
- 6AQ5/EL90: Slightly lower power rating but often usable as a replacement
- 6F6: An older tube with comparable performance in some applications
- EL84/6BQ5: Different pinout but sometimes adaptable as a substitute
When substituting tubes, it's important to consider not just electrical compatibility but also physical dimensions, pin configuration, and thermal characteristics. In some cases, circuit modifications may be necessary to accommodate a substitute tube safely.
Notable Characteristics
The CV2136/6BW6 is known for several distinctive characteristics that have contributed to its reputation among audio enthusiasts and electronics professionals:
Audio Performance
- Warm Sound Signature: Many audiophiles prize the tube for its smooth, warm sound reproduction
- Good Linearity: The beam tetrode design provides relatively low distortion compared to some contemporaries
- Responsive Dynamics: Quick response to transient signals makes it suitable for detailed audio reproduction
Reliability and Durability
- Robust Construction: Particularly in Brimar versions, known for solid build quality
- Long Service Life: When operated within specifications, these tubes can provide thousands of hours of service
- Stable Operation: Less prone to microphonics than some other audio tubes
Collector Interest
The Brimar-manufactured CV2136 tubes are particularly sought after by collectors and audio enthusiasts for their perceived superior construction and sound quality. NOS (New Old Stock) examples command premium prices in the vintage audio market, especially those with original military or Brimar markings and packaging.
Modern interest in these tubes has been sustained by the continuing popularity of tube audio equipment among audiophiles seeking the characteristic "tube sound" that solid-state devices struggle to replicate. The CV2136's moderate power output makes it particularly suitable for smaller amplifiers and single-ended designs that have seen a resurgence in popularity in recent decades.
