1. Introduction and History
The 5Z4G is a full-wave rectifier vacuum tube that was widely used in power supply circuits of radio receivers, amplifiers, and other electronic equipment during the mid-20th century. Developed in the 1930s, the 5Z4G belongs to the family of directly heated rectifier tubes that were essential components in vacuum tube-based electronics before the advent of solid-state rectifiers.
The 5Z4G was manufactured by various companies including RCA, Mullard, GEC, and more obscure manufacturers like Nore Electric of Southend. The British military designation CV1863 was assigned to the 5Z4G tubes that met specific military specifications. The Nore Electric manufactured CV1863 variant is particularly rare, with very few specimens known to exist today, making it a prized possession for tube collectors and historians.
2. Technical Specifications and Design
The 5Z4G is a glass envelope (bulb) full-wave rectifier with an octal base (8 pins with a central alignment key). Its key specifications include:
- Filament/Heater: 5.0 volts at 2.0 amperes
- Maximum AC Voltage Per Plate: 450 volts RMS
- Maximum DC Output Current: 125 mA
- Maximum Peak Inverse Voltage: 1400 volts
- Voltage Drop: Approximately 20 volts at 125 mA
- Base: International Octal (IO)
- Pin Configuration:
- Pin 1: No connection
- Pin 2: Filament
- Pin 3: No connection
- Pin 4: No connection
- Pin 5: Plate 1
- Pin 6: Plate 2
- Pin 7: No connection
- Pin 8: Filament
The 5Z4G features a directly heated cathode (filament) that serves as the electron emitter. The tube contains two separate anodes (plates) that alternately conduct during each half-cycle of the AC input, resulting in full-wave rectification. The internal construction includes a robust filament structure and plate design capable of withstanding high voltage and providing reliable service life.
3. Applications and Usage
The 5Z4G was primarily employed in the following applications:
- Radio Receivers: Used in the power supply sections of AM/FM radio receivers to convert AC mains voltage to the DC voltages required by the other tubes in the circuit.
- Audio Amplifiers: Commonly found in the power supply stages of hi-fi and guitar amplifiers, where it provided the high voltage DC for the output and preamp stages.
- Test Equipment: Utilized in oscilloscopes, signal generators, and other laboratory equipment that required stable DC power.
- Military Communications: The CV1863 variant was specifically used in military radio and radar equipment, where reliability under harsh conditions was paramount.
In typical usage, the 5Z4G would be connected to a power transformer's high-voltage secondary winding, with a center tap connected to ground. The rectified output would then be filtered by capacitors and possibly chokes to provide smooth DC voltage to the rest of the circuit.
4. Equivalent or Substitute Types
Several tubes can be used as direct or near-direct replacements for the 5Z4G:
- 5Z4GT: A tubular glass version with identical electrical characteristics
- 5Y3GT: Can substitute in many applications, though it has a lower maximum current rating (125 mA vs. 100 mA)
- 5V4G/5V4GA: Higher current capability (175 mA) but otherwise electrically compatible
- 5AR4/GZ34: Higher performance substitute with lower voltage drop, but may require circuit modifications
- U52: British equivalent to the 5Z4G
- 5T4: Similar characteristics but with slight differences in ratings
- 80: An earlier rectifier that can sometimes be used with caution regarding maximum voltage ratings
When substituting, care must be taken to ensure that the replacement tube's specifications (particularly maximum voltage and current ratings) are compatible with the circuit requirements.
5. Notable Characteristics
The 5Z4G possesses several distinctive characteristics that made it popular during its era:
- Reliability: Known for its robust construction and long service life, particularly important in military applications.
- Moderate Voltage Drop: The tube exhibits approximately 20 volts of drop under load, which is lower than some contemporaries like the 5Y3.
- Warm-up Characteristics: The 5Z4G has a relatively quick warm-up time, which helps protect other components in the circuit from voltage surges.
- Heat Dissipation: The tube generates significant heat during operation, requiring adequate ventilation in equipment designs.
- Distinctive Glow: During operation, the 5Z4G produces a characteristic purple-blue glow from the plates and a warm orange glow from the filament, appreciated by enthusiasts.
The Nore Electric manufactured CV1863 variant is particularly notable for its extreme rarity. Nore Electric was a smaller British manufacturer, and their tubes are seldom encountered today. This makes the Nore Electric 5Z4G/CV1863 a significant historical artifact representing a lesser-known chapter in vacuum tube manufacturing history.
For collectors and vintage audio enthusiasts, original 5Z4G tubes in good condition are highly sought after, both for their reliable performance in restoration projects and for their historical significance in the evolution of electronic technology.
