Big Thumb TH-20 – Natural, Early Vintage, 1974

Thumb TH-20 is a Japanese acoustic guitar, manufactured in 1974 at the Terada Gakki factory. This model belongs to the "Big Thumb" series, identified by the characteristic logo on the headstock (a shield with a thumbprint). The instrument features a soundbox with a spruce top plate and mahogany back and sides. After our service work, which included fingerboard leveling, refretting, and crafting natural bone nuts, the guitar is ready to play.

Technical specification

• Manufacturer: Thumb
• Model: TH-20
• Year of production: 1974
• Body: Spruce / Mahogany
• Neck: Nato
• Fingerboard: Rosewood
• Frets: Medium (Condition: 100% – new)
• Pickups: None
• Electronics: None
• Visual condition: Visible signs of use (details in description)
• Finish: Natural
• Weight: 2.09 kg / 4.61 lbs

Body and construction The Dreadnought-shaped soundbox features a top plate made of spruce, with the back and sides made of mahogany. The instrument is finished with a clear lacquer (Natural). Inside the soundbox, a traditional bracing system is used. A standard glued neck construction (Set-Neck) is applied. In our workshop, the lacquer coating went through a cleaning and waxing process.

Neck and ergonomics The Nato wood neck features a profile similar to a gentle "V" (Soft V). The neck is paired with a rosewood fingerboard. As part of the service work, the old frets were removed, the fingerboard was leveled, and brand new Blacksmith frets (2.1 mm) were installed. A new nut made of natural bone with a width of 43.3 mm was also fitted. The fingerboard surface was cleaned and conditioned.

Sound The instrument is a fully acoustic guitar with no electronic circuit.

• Characteristics: The use of a spruce top and mahogany back and sides in a large Dreadnought body generates a balanced frequency response with clear mids and a warm bottom end.
• Dynamics: The guitar responds appropriately to varied articulation strength, maintaining frequency clarity during both fingerstyle playing and strumming with a pick.

Additional information

The Thumb brand, including the Big Thumb series, was an in-house line (house brand) of the Terada Gakki factory, designed and distributed exclusively for the Japanese domestic market.

Instruments from this series aimed to showcase the production capabilities of the factory, which at that time primarily built instruments as a subcontractor (OEM) for other Western companies.

Crafting components from natural bone (nut and saddle) physically improves the transfer of vibrations from the strings to the soundbox compared to standard synthetic materials.

The service work we performed included: fingerboard leveling, complete refretting, crafting a bone nut and saddle, and setting the string action.

Hardware

• Bridge: Rosewood – the bridge features a custom-made saddle crafted from natural bone in our workshop.
• Tuners: Closed-gear Gotoh mechanisms in a 3+3 layout. The chrome hardware went through a cleaning process and retains its mechanical efficiency.

Instrument condition

• Technical condition: The instrument is mechanically functional after a luthier verification. The truss rod works properly, and the frets are brand new.
• Visual condition: The guitar shows signs of use appropriate for its age (50 years). Minor scratches and dings are visible on the lacquer coating. The instrument has no structural wood cracks.
• Setup and Modifications: Refretting (Blacksmith), crafting of bone nuts, fingerboard leveling, and a setup of the string action were performed. According to verification, the instrument retains its original factory structural specification (apart from the replaced consumable parts).

Why choose this instrument

• Big Thumb series: Rarer instruments from the Terada Gakki factory's in-house line, serving as proof of the historical quality of 1970s Japanese craftsmanship.
• Mahogany body: The use of this wood on the back and sides provides a warmer sound characteristic when paired with a spruce top.
• New frets and leveling: The complete replacement of frets and fingerboard leveling eliminate the wear resulting from use and ensure proper intonation.
• Ready to play: After our service work, the guitar is fully prepared for regular playing without the need for luthier visits after purchase.