Dynaco
David Hafler's mission to make tube audio affordable
History
Dynaco was founded in Philadelphia, Pennsylvania in 1955 by David Hafler, a brilliant engineer who had previously worked at Acrosound designing transformer-coupled amplifiers. Hafler's vision was radical: to produce high-quality audio equipment that ordinary people could afford.
The company's business model was equally innovative. Dynaco sold amplifiers primarily as kits, eliminating the cost of factory assembly while maintaining quality through well-designed PCBs and thorough documentation. Customers could save 30-40% by building their own equipment.
The ST-70 (Stereo 70) tube amplifier, introduced in 1959, became the best-selling tube amplifier in history. With 35 watts per channel and a simple, reliable design using EL34 output tubes, the ST-70 sold over 350,000 units over its 17-year production run. It remains the most popular vintage tube amplifier for restoration and modification.
The PAS-3 preamplifier (1963) and FM-3 tuner completed a complete high-fidelity system for under $200—an unprecedented value. Dynaco also produced the Mark III mono blocks and Mark IV mono amplifiers for those wanting more power.
In the 1970s, Dynaco expanded into speakers with the A-25 and A-35, Scandinavian-designed bookshelf speakers that offered exceptional value. The company also produced solid-state amplifiers like the ST-120 and ST-150.
Tandy Corporation (RadioShack) acquired Dynaco in 1983, and the brand eventually faded. However, the ST-70 and other Dynaco classics remain central to the vintage audio hobby, with countless units still in service and an active restoration community.
Key Facts
- Founded: 1955, Philadelphia, Pennsylvania
- Founder: David Hafler
- Business Model: High-quality kits at affordable prices
- Best Seller: ST-70 (350,000+ units)
- Philosophy: High-end audio for everyone
- Legacy: Most popular tube amp ever made
Legendary Products
Dynaco ST-70 (1959-1976)
The best-selling tube amplifier in history. The Stereo 70 delivered 35 watts per channel from four EL34 output tubes in a push-pull ultralinear configuration. Its simple, reliable circuit and excellent transformers made it the gateway to tube audio for generations.
Dynaco PAS-3 (1963-1980s)
The companion preamplifier to the ST-70. The PAS-3 offered multiple inputs, bass and treble controls, and a warm, musical sound that complemented the ST-70 perfectly. The PAS-3X added a cathode-follower output stage.
Dynaco A-25 (1968-1970s)
A bookshelf speaker designed by Seas of Norway. The A-25 used a 10" woofer and 3/4" dome tweeter in a sealed enclosure, offering remarkable bass response from a compact cabinet. It became one of the best-selling speakers of the 1970s.
Dynaco Mark III (1960s)
Monoblock tube amplifiers delivering 60 watts each from a pair of EL34 tubes. The Mark III offered more power than the ST-70 for those with larger speakers or rooms. Often used in pairs for stereo.
Classic Models Reference
- ST-70: 1959-76, Tube Amp, 35WPC, Most popular tube amp
- Mark III: 1960s, Mono Amp, 60W, Monoblock power
- Mark IV: 1960s, Mono Amp, 40W, Smaller monoblock
- PAS-3: 1963-80s, Preamp, Classic tube pre
- PAS-3X: 1960s, Preamp, With cathode follower
- FM-3: 1960s, Tuner, Tube FM tuner
- AF-6: 1960s, Tuner, AM/FM version
- SCA-35: 1960s, Integrated, 17WPC, Compact tube amp
- ST-120: 1970s, Solid State, 60WPC, Transistor amp
- ST-150: 1970s, Solid State, 75WPC, Bigger solid state
- A-25: 1968-70s, Speaker, Seas drivers
- A-35: 1970s, Speaker, Larger A-25
- A-50: 1970s, Speaker, Floorstanding
Sound Signature
Dynaco equipment is characterized by:
- Tube warmth - Classic EL34 character
- Musicality - Engaging, enjoyable sound
- Value engineering - Maximum performance per dollar
- Reliability - Simple, serviceable designs
- Accessibility - Gateway to high-end audio
Collecting Dynaco
Vintage Dynaco gear is valued for:
- ST-70 amplifiers - The classic tube amp
- Original condition - Unmolested examples
- Kit vs. Factory - Factory-built worth more
- Restoration potential - Excellent for learning tube electronics
- PAS-3 preamps - Perfect match for ST-70
Most collectible models:
- ST-70 - The people's tube amp
- Mark III - Monoblock power
- PAS-3 - Classic tube pre
- A-25 - Scandinavian value
Restoration Tips
Common Dynaco service items:
- Replace capacitors (all electrolytics, signal caps optional)
- Check tubes (replace if weak)
- Verify bias adjustment (critical for tube life)
- Replace selenium rectifiers with modern silicon
- Update bias pots (original wire-wound often noisy)
- Consider modern PCBs (many upgrade options available)
Competitors & Comparisons
Dynaco vs Heathkit: Both kit companies; Dynaco more audiophile-focused
Dynaco vs Eico: Similar market; Dynaco more successful
Dynaco vs McIntosh: McIntosh luxury; Dynaco accessible quality
All Models in Archive (16)
| STEREO-80 | 1959 |
| AF-6 (AM/FM Tuner) | 1965 |
| AF-6 | 1963 |
| CAB-1S | 1975 |
| FM-3 | 1964 |
| MK-II | 1965 |
| MK-VI | 1975 |
| PAS-2 | 1960 |
| PAT-4 | 1967 |
| PAT-5 | 1976 |
| QD-1 (Quadaptor) | 1970 |
| SCA-80Q | 1972 |
| ST-120 | 1966 |
| ST-35 | 1959 |
| ST-70 (Stereo 70) | 1959 |
| ST-80 | 1967 |
Amplifiers
Amplifiers
- AF-6 (AM/FM Tuner) - 1965
- MK-II - 1965
- MK-VI - 1975
- PAS-2 - 1960
- PAT-4 - 1967
- PAT-5 - 1976
- SCA-80Q - 1972
- ST-120 - 1966
- ST-35 - 1959
- ST-70 (Stereo 70) - 1959
- ST-80 - 1967
- STEREO-80 - 1959
Speakers
- CAB-1S - 1975
Tuners
Turntables
- QD-1 (Quadaptor) - 1970