This is a Slow Blow 3AG 1/2 AMP fuse. This fuse can serve as a suitable replacement fuse for your vintage amplifier. This item protects your amplifier if the amplifier's current overloads it's limit by making an open circuit in a matter of a few seconds.
Time Current Characteristic: Slo-Blo Amperage: 1/2 AMP Voltage Rating: 250 Volts Tube: Ceramic Leads: Tin–Plated Copper End Caps: Nickel-Plated Brass Operating Temperature: –55ºC to +125ºC