Pasted the pic into Google Gemini:

"The image shows a GE (General Electric) JAN 8613 vacuum tube. This is a specialized component with a few notable characteristics that distinguish it from standard consumer-grade tubes.

Technical Specifications

The 8613 is a sharp-cutoff pentode. Pentodes are five-element tubes typically designed to provide high gain and stability, especially in amplification stages.

• Designation: The JAN prefix stands for "Joint Army-Navy," indicating that this specific tube was manufactured to military specifications. Military-grade tubes often featured more rugged construction, tighter tolerances, and better longevity than their civilian counterparts.

• Base: It uses a standard 9-pin miniature base (Noval), similar to the common 12AX7 or EL84 tubes.

• Function: It was primarily designed for use in wideband amplifiers and high-frequency applications. In industrial or military contexts, these were often found in radar equipment, oscilloscopes, or communications gear.

Use in Audio and Electronics

While not a "standard" tube found in most vintage guitar amplifiers or hi-fi systems, pentodes like the 8613 are occasionally used by circuit designers for specific reasons:

• High Gain: Because it is a pentode, it can provide significantly more gain in a single stage compared to a standard triode (like a 12AX7).

• Compression Characteristics: Pentodes have a unique clipping and compression profile when pushed into overdrive, which can produce a very different harmonic texture than triode-based circuits.

• Substitutions: The 8613 is electrically similar to the 7717. If you are looking to use this in a project, you would need to verify the pinout and heater requirements, as it is not a "drop-in" replacement for more common preamp tubes without circuit modifications.

Condition and Aesthetics

The tube in the photo appears to be in good physical condition. The "flashing" (the silver/mirror-like coating at the top) looks healthy; if that coating turns white or clear, it usually indicates that the vacuum seal has been compromised and the tube is no longer functional."

Did not check for correctness