McIntosh 50W-1 (1949–1950)
A vacuum tube stereo power amplifier, notable as McIntosh Laboratory’s first product.
Overview
The McIntosh 50W-1 is the company's first product, developed after founder Frank McIntosh became dissatisfied with the distortion and limited power of existing amplifiers. Introduced in 1949, it established key design principles that would define the brand. Though marketed as a stereo amplifier, it delivers 50 watts per channel in stereo mode and up to 150 watts in mono. It features a unique Unity Coupled Circuit output transformer design, which allows full power delivery across the entire audio spectrum while maintaining low distortion and protecting connected speakers.
Specifications
| Rated output stereo (8 Ω) | 50W + 50W |
| Rated output mono (8 Ω) | 150W |
| Output load impedance | Stereo : 2 Ω, 4 Ω, 8 Ω, 16 Ω; Mono : 1 Ω, 2 Ω, 4 Ω, 8 Ω |
| Rated output band | 20 Hz to 20 kHz |
| Total harmonic distortion | Not more than 0.002% |
| Cross modulation distortion factor | 0.1% or Less (at Rated Output) |
| Frequency response (at 1W output) | 20 Hz ~ 20 kHz + 0 -0.25 dB; 10 Hz ~ 100 kHz + 0 -3.0 dB |
| Signal-to-noise ratio | 95 dB or more (at rated output) |
| Damping factor | Stereo : 16 (2 Ω), 50 (4 Ω), 20 (8 Ω), 14 (16 Ω); Mono : 16 (1 Ω), 50 (2 Ω), 20 (4 Ω), 14 (8 Ω) |
| Input Sensitivity / Impedance | 0.75 V, 2.5V/75k Ω (Switched by level control) |
| Power | 120 VAC, 50Hz/60Hz |
| Power consumption | 50W (no signal); 460W (at maximum rated output) |
| External dimensions | Width 445x Height 152x Depth 467 mm |
| Weight | 25.9 kg (net) |
Design
The 50W-1 uses a patented "Unity Coupled Circuit" output transformer design that enables consistent power delivery across all frequencies and speaker impedances while minimizing distortion. The output transformer also protects speakers in case of amplifier failure. It includes a Power Guard system with a waveform comparison circuit that monitors the difference between input and output signals. When distortion reaches 0.5%, the Limit (red) lamp illuminates; at 1%, the system activates to prevent clipping and speaker damage, all while maintaining rated output. The amplifier uses a differential input stage with low-noise tubes and a single-ended para-push output circuit with six complementary service power tubes.
Context
As the first product from McIntosh Laboratory, the 50W-1 set the foundation for the company's reputation in high-fidelity audio. It was developed to solve the problems of distortion and inadequate power in contemporary amplifiers, marking a significant advancement in amplifier design at the time.
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