KLH Model Twenty One FM Radio
The KLH Model Twenty One FM Radio is a tabletop FM tuner introduced in 1961 and produced until 1976. Henry Kloss designed it. It is a compact solid-state receiver in a minimalist walnut veneer cabinet, known for warm, clear FM reception. It 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 Model Twenty One came out in the early 1960s, when FM broadcasting was gaining ground on AM for sound quality. Henry Kloss, a co-founder of Acoustic Research and later KLH, designed it to deliver exceptional tuner performance in a compact, good-looking package.
Most consumer radios of the era still used tubes. The Model Twenty One used solid-state circuitry, which meant better reliability and less maintenance. The precision slide-rule tuning dial allowed accurate station selection, and the built-in ferrite antenna pulled in strong reception without anything external. The warm, musical sound and low distortion made it a favorite among audiophiles and casual listeners alike.
It was one of KLH's most successful products and stayed 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 known for its warm, clear, and musical FM reception. The solid-state design gives low distortion and an excellent signal-to-noise ratio for its era. It does well on weak stations, and its stereo separation (when paired with a stereo decoder) is impressive by vintage standards. It is small, but the sound is full and engaging, particularly with classical, jazz, and acoustic music.
Maintenance and Restoration Tips
Because of its age, the KLH Model Twenty One often needs some maintenance to restore good 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.
Power the unit up through a variac or current limiter during initial testing. That protects it from damage caused by latent faults.
Collectibility and Market Value
The KLH Model Twenty One is highly collectible and earns an 8/10 on the vintage audio collectibility scale. The design, the Henry Kloss pedigree, and the long production run all add to its 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 Model Twenty One has an elegant design, solid engineering, and superb tuner performance, which keeps it popular with vintage audio enthusiasts. People use it as a daily driver or display it as a design piece.
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