1. Introduction and History
The EZ35 (also known by its military designation CV1100) is a full-wave rectifier vacuum tube that was manufactured primarily by European companies like Mullard, Philips, and Mazda during the mid-20th century. Developed in the late 1930s and widely used through the 1950s, the EZ35 was part of the E-series of tubes that featured 6.3V heaters, standardized by Philips and adopted throughout Europe.
The EZ35 gained popularity in British and European radio and audio equipment, particularly in AC-powered receivers and small amplifiers where its compact size and reliable rectification capabilities made it an ideal choice. Mullard, a prominent British manufacturer (later acquired by Philips), was one of the main producers of this tube type, creating high-quality versions that were known for their durability and consistent performance.
2. Technical Specifications and Design
The EZ35 is a directly heated, full-wave rectifier vacuum tube with the following specifications:
- Heater Voltage: 6.3V
- Heater Current: 0.6A
- Maximum AC Input Voltage (per plate): 350V RMS
- Maximum DC Output Current: 70mA
- Maximum Peak Inverse Voltage: 1000V
- Internal Resistance: Approximately 300 ohms
- Base Type: International Octal (IO) 8-pin
- Envelope: Glass, ST-12 shape
- Pin Configuration:
- Pin 2: Heater
- Pin 7: Heater
- Pin 4: Cathode
- Pins 1 and 6: Anodes (plates)
The EZ35's design features two separate diode sections sharing a common cathode, allowing it to perform full-wave rectification. The directly heated cathode emits electrons when heated by the filament, which are then attracted to the positively charged anodes. The tube converts alternating current (AC) to direct current (DC) by allowing current to flow only when the anodes are positive with respect to the cathode.
The tube's relatively low maximum current rating of 70mA makes it suitable for smaller power supplies rather than high-power applications. Its voltage drop is approximately 20V at full load, which needs to be accounted for in power supply design.
3. Applications and Usage
The EZ35 was commonly used in:
- Radio Receivers: Particularly in European domestic radio sets from the 1940s and 1950s, where its modest current capability was sufficient for small to medium-sized receivers.
- Small Audio Amplifiers: The tube found applications in low-power audio amplifiers, especially those using other E-series tubes like the EL33, EL34, or EL84.
- Test Equipment: Various measurement and laboratory devices utilized the EZ35 for their power supply sections.
- Military Communications Equipment: Under its CV1100 designation, the tube was used in various British military radio and communications equipment.
In typical applications, the EZ35 would be configured in a conventional full-wave rectifier circuit with a center-tapped transformer. The center tap of the high-voltage secondary winding connects to ground, while the two ends of the winding connect to the two anodes of the EZ35. The cathode then provides the rectified DC output, usually followed by a filter network consisting of capacitors and chokes or resistors to smooth the pulsating DC.
4. Equivalent or Substitute Types
Several tubes can serve as direct or near-equivalent substitutes for the EZ35:
- 6X5GT: The American equivalent to the EZ35, with very similar electrical characteristics. The 6X5GT is often considered a direct replacement and is mentioned in the product listing as related to the EZ35.
- 6X5G: The earlier, larger glass envelope version of the 6X5GT with identical electrical specifications.
- 6X5: The metal envelope version of the same tube.
- CV1100: Military designation for the EZ35.
- EZ2: Similar European rectifier but with slightly different characteristics.
- 5Y3GT: While not a direct replacement (it has higher current capability but requires a 5V heater), it can sometimes be used with circuit modifications.
When substituting tubes, it's important to consider not just the electrical characteristics but also the physical dimensions and pin configuration. While the EZ35 and 6X5GT share the same octal base and similar dimensions, other potential substitutes may require socket adapters or circuit modifications.
5. Notable Characteristics
The EZ35 has several distinctive characteristics that define its performance and application:
- Warm-up Time: As a directly heated tube, the EZ35 has a relatively quick warm-up time compared to indirectly heated rectifiers, allowing for faster equipment startup.
- Voltage Drop: The tube exhibits a voltage drop of approximately 20V at full load, which must be factored into power supply design calculations.
- Reliability: Particularly in Mullard-manufactured versions, the EZ35 was known for its robust construction and long service life, often operating reliably for thousands of hours.
- Current Limitation: The 70mA maximum current rating is a significant limitation, restricting its use to smaller equipment. This is considerably less than other common rectifiers like the 5Y3GT (125mA) or 5U4G (225mA).
- Heat Generation: The tube generates moderate heat during operation, requiring adequate ventilation in the equipment chassis.
- Voltage Surge Resistance: The EZ35 has good resistance to voltage surges, enhancing its reliability in applications where power line fluctuations might occur.
Mullard-manufactured EZ35 tubes, as referenced in the product information, are particularly sought after by vintage audio enthusiasts and collectors for their quality construction and consistent performance characteristics. When tested on specialized equipment like AVO tube testers (as mentioned in the product listing), these tubes often show remarkable consistency in their parameters even after decades of storage.
Today, the EZ35 is primarily of interest to vintage equipment restorers, audio enthusiasts building or maintaining tube-based equipment, and collectors of vacuum tube technology. While no longer in production, new old stock (NOS) examples can still be found through specialty suppliers and auction sites, allowing the continued operation of equipment originally designed around this reliable rectifier tube.
