A tube monaural power amplifier developed as an improved version of the MB8A developed in the monaural era.
The output tube uses GE's KT-88, which has a maximum output of 85W and is relatively light in use, giving it excellent and spacious characteristics.
The output circuit uses a cathode NF method.
The MB88 uses a special type OY36 type with a cathode NF coil added to the output transformer, and a cathode NF coil is applied to the KT-88. The cathode NF method is a multiple NF method in which the internal resistance of the output tube itself is lowered in advance by applying local NFB to the output tube, and then NFB is applied over all stages from above.
By this method, an effect almost equivalent to using a triode tube with low internal resistance and little distortion has been obtained. What's more, it has the advantage of being able to output as much as a multi-electrode tube, and this circuit is also used in Macintosh's MC-275.
Stability is increased by adopting a unique crossover NFB method.
Equipped with input level set function.
The main body is designed with a chrome pipe around it, with the top of the pipe functioning as a handle and the bottom functioning as a leg.
The design of the logo on the panel surface was different between the first half and the second half.
Specifications
| Model | Tube monaural power amplifier | ||
| Circuit method | Multi-NF method | ||
| Continuous effective output | 85W(55Hz) | ||
| Total harmonic distortion | 0.5% or less (85W) | ||
| Frequency characteristic | 20Hz～20kHz -0.5dB | ||
| NF amount | 27dB (cathode NF6dB, major NF21dB) | ||
| Input sensitivity | 900mV (85W, 1kHz) | ||
| input impedance | 100kΩ | ||
| S/N ratio | 90dB or more | ||
| load impedance | 4Ω, 8Ω, 16Ω | ||
| Attached equipment | input level set | ||
| Vacuum tubes used etc. |
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| power consumption | 120W (at no signal) 230W (at maximum output) |
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| External dimensions | Width 445x Height 246x Depth 198mm | ||
| weight | 17kg |
https://audio-heritage.jp/LUXMAN/amp/mb88.html
