A defective vacuum tube in a transmitter may be indicated by?

• A. Gas glow within the tube
• B. No light from the filament
• C. Reduced output
• D. All of the above

Answer: (D)

A defective vacuum tube in a transmitter can manifest in various ways, and each of the indicators mentioned provides important clues about potential issues.

When there is gas glow within the tube, it suggests that there's a problem with the vacuum integrity. A proper vacuum is crucial for the tube to function correctly; any gas presence can lead to faults in performance.

The absence of light from the filament indicates that the filament is not heating up properly. This could mean that the filament itself is burnt out or that there are issues with the connections, either of which would prevent the tube from operating.

Reduced output from the transmitter is perhaps the most evident sign of a malfunctioning vacuum tube. When the tube is unable to operate effectively due to any of the aforementioned issues, it will not amplify the signal as intended, resulting in decreased output.

Each of these indicators—gas glow, no filament light, and reduced output—points to a potential defect in the vacuum tube. Therefore, it is valid to conclude that a defective vacuum tube could potentially be indicated by all of the mentioned symptoms.