The RCA Receiving Tube Manual RC-21, published in 1961, is a comprehensive reference guide for vacuum tube enthusiasts, engineers, technicians, and hobbyists. Developed by RCA, a prominent manufacturer of electron tubes, this manual provides detailed information about various types of receiving tubes produced by RCA and other manufacturers.

Key features of the RCA Receiving Tube Manual RC-21 include:

1. Tube Data: The manual contains extensive data on receiving tubes, including specifications such as filament voltage, plate voltage, grid voltage, maximum plate dissipation, and typical operating conditions. This information is essential for designing and troubleshooting electronic circuits.

2. Tube Characteristics: It includes characteristic curves for different tubes, illustrating their performance under various operating conditions. These curves help users understand how the tubes behave and how to optimize their performance in electronic circuits.

3. Application Notes: The manual offers practical application notes and circuit diagrams for using receiving tubes in different types of audio and radio-frequency circuits. This includes amplifier circuits, oscillator circuits, mixer circuits, and more.

4. Cross-Reference Tables: It features cross-reference tables that allow users to identify equivalent tubes from different manufacturers. This is useful for finding suitable replacement tubes or for sourcing tubes that may no longer be in production.

5. Technical Information: The manual provides technical information on tube construction, materials, and manufacturing processes, offering insights into the technology behind vacuum tubes.

6. Index and Appendices: It typically includes a comprehensive index for easy reference, as well as appendices containing additional useful information such as tube base diagrams, socket pinouts, and glossaries of terms.

Overall, the RCA Receiving Tube Manual RC-21 is a valuable resource for anyone working with vacuum tubes, providing essential data, application notes, and technical insights to support the design, maintenance, and repair of electronic equipment using vacuum tube technology.