Gibson GA-15 RVT Explorer (Vintage)

From the renowned collection of Indigo Ranch (labelled "Indigo" in marker in several places.) Cool 60's-era tube amp with reverb and tremolo. Single 10-inch CTS speaker marked "Gibson Ultrasonic." Tubes are 6BQ5 (2), 12AU7, and 6EU7 (2). Cosmetically in pretty nice shape; appears to be all original; original reverb/tremolo pedal is present in "holster"; grill cloth and tolex are in very nice condition; one knob is missing. Powers up, passes signal (reverb and tremolo both work) but signal is "tinny" and weak. Likely a straightforward fix.