Dynaco Mark III
A monoblock tube power amplifier released by Dynaco in 1957, designed for high-fidelity stereo systems.
Overview
The Dynaco Mark III is a monoblock tube power amplifier developed by Dynaco, a company founded in 1955 by David Hafler and Ed Laurent in Philadelphia, PA. Released in 1957, it was engineered to deliver more power than the popular ST-70 stereo amplifier, making it a preferred choice for audiophiles seeking higher performance. Often used in pairs for stereo setups, the Mark III is part of a series that includes the Mark IV mono amplifiers. It was selected by Acoustic Research (AR) for their live-vs.-recorded demonstration programs, highlighting its reputation for accuracy and robustness.
Specifications
| Power output | 60 watts (rated) |
| Output tubes | 6550 / KT88 (2 pieces) |
| Tube complement | 6550/KT88 (2), 6AN8 (1), GZ-34/5AR4 (1) |
| Total harmonic distortion | ≤ 0.5% (60W, 20Hz-20kHz) |
| Cross modulation distortion | ≤ 1% (Rated Output), ≤ 0.5% (50W), ≤ 0.05% (1W) |
| Frequency response | 6 Hz to 60 kHz ± 0.5 dB |
| Input sensitivity | 1.6V (for 60W output) |
| Signal-to-noise ratio | ≥ 90 dB (at rated output) |
| Output impedance | 4 Ω, 8 Ω, 16 Ω |
| Damping factor | 15 |
| Power consumption | 150W |
| Dimensions (W x H x D) | 229 x 190 x 229 mm |
| Weight | 13.5 kg |
Design
The Mark III uses a push-pull output stage and includes a power supply capable of powering a preamplifier. It was built with varying output transformer types depending on production period, including models A-431, Z-216, and ZT0195. The amplifier uses a P-782 power transformer and contains a rectifier tube as part of its tube complement.
Context
Dynaco introduced the Mark III to meet demand for higher-powered amplification in high-fidelity audio systems. Early production models used transformers from TRESCO due to patent conflicts with Acrosound. It has been noted as having higher production volume than any other tube monoblock amplifier of its era.
Market
Originally priced at $83.95 each, the Mark III remains actively traded in the vintage audio market. Units described as restored or completely rebuilt have been listed for up to $1,595 for a pair. A known failure mode involves immediate fuse blowout upon power-up—even with the rectifier tube removed—indicating possible miswiring or a defective P-782 power transformer.
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