Dynaco Mark-III (1957)
A tube-powered monaural amplifier delivering 60 watts of rated output, introduced by Dynaco in 1957.
Overview
The Dynaco Mark-III is a tube-type monaural power amplifier released in 1957 by Dynaco, a company founded in Philadelphia in 1955 by David Hafler. Known for its high power output compared to other models of its time, the Mark-III was often used in pairs to achieve stereo sound and was positioned above the ST-70 in Dynaco’s lineup. It was designed for users with larger speakers or rooms and was also distinct from the later Mark IV mono amplifier. According to historical accounts, the Mark-III became one of the most widely acclaimed high-power amplifier designs in high-fidelity audio history.
Specifications
| Output | 60W (Rated) 140W (peak) |
| Total harmonic distortion factor | 0.5% or Less (60W, 20 Hz ~ 20 kHz) |
| Cross modulation distortion factor | 1% or Less (Rated Output) 0.5% or less (at 50W output) 0.05% or Less (at 1W Output) |
| Frequency characteristic | 6 Hz to 60 kHz ± 0.5 dB / 16 Hz ~ 25 kHz ± 0.5 dB (Maximum Output) |
| Input sensitivity | 1.6V(60W) |
| Signal-to-noise ratio | 90 dB or more (at rated output) |
| Output impedance | 4 Ω, 8 Ω, 16 Ω |
| Damping factor | 15 |
| Vacuum tube used | 6550 (KT-88) : 2 pieces / 6AN8 : 1 Piece / GZ-34 (5AR4) : 1 piece |
| Power consumption | 150W |
| External dimensions | Width 229x Height 190x Depth 229 mm |
| Weight | 13.5 kg |
Design
The Mark-III uses a push-pull configuration with two 6550 (KT-88) tubes to achieve high power output. The output transformer varies by production period, with models including A-431, Z-216, and ZT0195 used over time. The unit includes a power supply for a preamplifier, enabling integration into a complete tube-based audio system.
Context
When the Mark-III launched in 1957, Acrosound output transformers were unavailable due to patent issues, so Dynaco partnered with TRESCO, a transformer manufacturer closely associated with the company, to supply units. The amplifier was sold primarily as a kit, consistent with Dynaco’s business model. It offered more power than the ST-70 and was part of a family that included the Mark III mono blocks and the separate Mark IV mono amplifier for users seeking even greater performance.
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Related Models
- Dynaco Stereo 70 (1959-late 1970s)
- Dynaco MK-VI (1975)
- Dynaco PAS-2 (1960)
- Dynaco STEREO-80 (1959)
- Dynaco AF-6 (AM/FM Tuner) (1965)
- Luxman L-530 (1975)
- Luxman R-404 (1975)
- Luxman RV-371 (1975)
- Luxman SQ-38U (1975)
- Luxman T-14 (1972)