Safety When Working with Valves
The reader needs to be aware of the potential dangers when working with equipment
Valves operate with high DC voltage, and for RF amplifiers, high RF voltage. The voltages typically used can be extremely hazardous and any contact with these is certain to lead to adverse affects to human life. It is therefore necessary to observe strict safety precautions when working with equipment of this type.
All equipment designed to be powered from the public mains supply must be correctly wired and grounded to the public mains earth. Fuses used should be appropriate for the equipment.
When testing or making measurement, often parts are exposed with hazardous voltage connected. Extreme caution needs to be used so as not to accidentally come in contact with these items.
If a protective cover needs to be removed to gain access to a portion of circuitry, the equipment must be powered down and high voltage reservoir capacitors should be discharged to ensure no lethal voltages are present.
If safety devices need to be ‘cheated’ to make the circuit operate, this must be only for the duration of the special test requirement.
In the case where a protective cover needs to be opened to allow access great care must be taken if the circuitry is subsequently powered up to assess the working conditions within the circuit. Anode circuitry of RF amplifiers emit strong electro-magnetic radiation with the covers removed. This can be harmful and operation with covers removed should be kept to a minimum.
All test equipment used must be suitable for the intended testing required and capable of withstanding the high voltages present. Many DVMs are not rated above 1kV AC or DC and hence special measuring equipment may be required.
It is preferable to have a second person close by in case of an incident, who can interrupt the operation by switching the equipment off should an emergency arise. If the person making the measurement is uncertain of any aspect, an experienced person should supervise the operation.
Valves contain a very high vacuum, which normally is safe. However, if undue stress is placed on a glass envelope it can break and the result will be an implosion. This can cause severe cuts and other injuries to a person nearby. Valves not in use should be stored in the manufacturer’s packing or carton until required for use. Care must be taken not to damage glass envelope valves when inserting or removing them from equipment. If disposing of a faulty valve, which may contain hazardous material, correct disposal methods must be followed. Your local legislation should be consulted about the steps that are required.
The author and the publisher cannot be held liable for any damage to person or property should an incident arise from working with valves.
- 1. Notes on Terminology
- 2. Safety When Working with Valves
- 3. 1: Introduction
- 4. 2: Basic Valve Theory
- 5. 3: Working with Valve Characteristic Curves
- 6. 4: The Class A Amplifier
- 7. 5: Operating Modes
- 8. 6: Causes of Distortion
- 9. 7: Measuring Amplifier Linearity
- 10. 8: Designing an Anode Tank Circuit
- 11. 9: Grounded Cathode Linear Amplifiers
- 12. 10: The Grounded Grid Amplifier
- 13. 11: Power Supply Design
- 14. 12: Protection Circuitry
- 15. 13: Liquid Cooling the Eimac 4CX250 Valves
- 16. 14: Purchasing an Amplifier
- 17. 15: Notes on RF Linear Amplifier Operation
- 18. 16: VHF RF Power Amplifiers