KLH Model Twenty One FM Radio

The KLH Model Twenty One FM Radio is a legendary tabletop FM tuner introduced in 1961 and produced until 1976. Designed by audio pioneer Henry Kloss, this compact solid-state receiver became a hallmark of mid-century hi-fi design and performance. Revered for its warm, clear FM reception and minimalist walnut veneer cabinet, the Model Twenty One brought high-fidelity radio into homes across America during the golden age of FM broadcasting.

Specifications

Feature	Specification
Year of Production	1961–1976
Manufacturer	KLH (Kloss Loudspeaker Company)
Designer	Henry Kloss
Type	FM Tuner (Tabletop)
Circuitry	Solid-state (transistorized)
Power Requirements	Tuner only – no internal amplification
Impedance	Not specified (tuner output)
Sensitivity	2.5 μV for 20 dB quieting (FM)
Tuning Method	Slide-rule style tuning dial
Antenna	Built-in ferrite bar antenna
Cabinet Material	Walnut veneer with steel chassis
Dimensions	13.5" W × 3.5" H × 7.5" D
Weight	7.5 lbs
Output	Line-level audio output (to external amplifier)

Historical Context

The KLH Model Twenty One emerged at a pivotal time in audio history—the early 1960s—when FM broadcasting was gaining traction for its superior sound quality over AM. Designed by Henry Kloss, a co-founder of Acoustic Research and later KLH, the Model Twenty One was engineered to deliver exceptional tuner performance in a compact, aesthetically pleasing package.

Unlike most consumer radios of the era, the Model Twenty One used solid-state circuitry, avoiding tubes for improved reliability and reduced maintenance. Its precision slide-rule tuning dial allowed for accurate station selection, while the built-in ferrite antenna delivered strong reception without external additions. The warm, musical sound and low distortion made it a favorite among audiophiles and casual listeners alike.

As one of KLH’s most successful products, the Model Twenty One remained in production for 15 years—an extraordinary run for a high-fidelity component. It played a key role in popularizing FM radio as a serious medium for music and helped define the look and sound of mid-century hi-fi.

Sound Signature

The Model Twenty One is celebrated for its warm, clear, and musical FM reception. Its solid-state design delivers low distortion and excellent signal-to-noise ratio for its era. The tuner excels at pulling in weak stations with clarity, and its stereo separation (when paired with a stereo decoder) is impressive by vintage standards. Despite its small size, it offers a surprisingly full and engaging listening experience, particularly with classical, jazz, and acoustic music.

Maintenance and Restoration Tips

Due to its age, the KLH Model Twenty One often requires some maintenance to restore optimal performance:

Capacitor Replacement: Electrolytic and paper capacitors degrade over time. Replacing these (especially in the power supply and audio coupling stages) is often essential for safe and reliable operation.
Cleaning Potentiometers: The tuning and volume controls can become noisy. Use electronic contact cleaner on the potentiometers, or consider replacement if worn.
Dial Cord Adjustment: The slide-rule tuning mechanism relies on a thin cord that can stretch or break. Replacing the dial cord ensures smooth and accurate tuning.
Transistor Testing: While generally reliable, early germanium transistors can fail. Check for proper bias and gain; replacements should match original specs.
Cabinet Care: The walnut veneer is prone to scratches and finish degradation. Clean gently with a wood-safe polish and avoid direct sunlight to prevent fading.
Antenna Performance: If reception is weak, ensure the internal ferrite antenna is intact and properly connected. External FM antennas can be added via the antenna terminals.

Always power on the unit through a variac or current limiter during initial testing to avoid damage from latent faults.

Collectibility and Market Value

The KLH Model Twenty One is highly collectible, earning an 8/10 on the vintage audio collectibility scale. Its iconic design, Henry Kloss pedigree, and long production run contribute to its enduring appeal.

Market Value: $100–$300 depending on condition
Fully restored units with clean cabinets and accurate tuning command higher prices
Original, unmodified examples are especially desirable
Units with damaged veneer or non-functional electronics may sell for parts or restoration

Conclusion

The KLH Model Twenty One FM Radio stands as a masterpiece of form and function from the golden age of hi-fi. Its elegant design, solid engineering, and superb tuner performance make it a cherished piece among vintage audio enthusiasts. Whether used as a daily driver or displayed as a design artifact, the Model Twenty One continues to deliver the warmth and clarity that defined a generation of audio excellence.