LUXKIT KMQ80
¥ 124,000 (released in October 1974)
Commentary
A bulb-tube amplifier kit is a kit of the tube type stereo power amplifier MQ80.
The output tube is a 6336A bi-triode with a large graphite electrode plate.
This ball has a large plate loss of 30W per one unit and 60W for both units. However, because this type of tube has a very narrow gap and is dense, it must be stable both in terms of material and structure so that the electrodes themselves cannot be deformed by vibration or heat. For this reason, KMQ80 has selected RAYTHEON tubes for use.
The output transformer employs a cross-shunt push-pull operation output transformer that was developed to maximize the performance of 6336A.
This transformer employs a bifilar winding, a special winding method, which is the same as the OY15 type in appearance. However, the internal structure is such that the primary winding of the output transformer is divided into the plate side and the carousel side, and these two windings are wound simultaneously. This method has succeeded in reducing distortion factor from small output power to large output power.
In addition, the frequency characteristic of the output transformer itself has been extended to 200 kHz, and the phase characteristic is also excellent. Therefore, in addition to improving the bare characteristics of the amplifier, the stability when negative feedback is applied is also excellent.
In the driver stage, a cathode follower direct-coupled circuit is adopted to realize a drive voltage without waveform distortion by keeping output impedance low. In addition, a large amount of voltage negative feedback is applied to this circuit, so that distortion and phase change are small, and direct coupling with the output tube is easy.
Since this direct-coupled circuit does not have a time constant at the coupling part, there is no transient phenomenon caused by this connection, and stable driving is possible even during overswing.
The KMQ80 has adopted a twin triode 12BH7A for this stage.
Since the gain cannot be obtained with the cathode follower direct-coupled circuit, the phase inversion stage is used to make up for the lack of gain. The KMQ80 uses the Mulard type, which can gain gain, and uses 6AQ8, which has a large amplification degree and relatively low internal resistance, to obtain a large output voltage. To balance the gain of the inversion circuit, the plate resistance is slightly changed to balance the output voltage.
The 5-pole tube 6267 is used for the first stage, and the phase inversion stage is directly coupled with it to reduce the low-frequency time constant circuit.
This is because a large gain is obtained at the first stage to increase the total gain, and at the same time, a relatively deep negative feedback of 22 dB is applied from the secondary side of the output transformer to the cathode of the first stage to improve the distortion factor characteristics without loss of stability.
A large power transformer is used for the power supply circuit, and the power supply for the output circuit is a bridge rectification system to optimize the regulation. The smoothing circuit also combines a choke coil with low DC resistance and a large electrolytic capacitor (330 μ Fx2) to reduce the power supply impedance and provide a stable circuit with less voltage fluctuation.
In addition, a protective circuit for protecting the output tube and a preheating circuit for the output tube are mounted.
Chip jack for operation check and input level set are mounted.
There was a special hood sold separately.
Model Rating
| Type | Bulb type power amplifier kit | ||
| Circuit system | Cross-shunt PP circuit | ||
| Continuous effective output | 40W/40W | ||
| Total harmonic distortion factor | 1% or Less (40W/40W, 1 kHz) 0.5% or Less (30W/30W, 1 kHz) |
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| Frequency characteristic | 10 Hz to 50 kHz - within 1 dB | ||
| Input Sensitivity / Impedance | Approximately 800mV/82k Ω | ||
| Residual noise | 1 mV or less | ||
| Damping factor | 15 (8 Ω Load) | ||
| Load impedance | 4 Ω, 8 Ω, 16 Ω | ||
| Attachment | Chip jack for operation check Input level set |
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| Used vacuum tubes, etc. |
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| Power consumption | 250W (350W at maximum output) | ||
| External dimensions | Width 435x Height 165x Depth 260 mm | ||
| Weight | 17kg | ||
| Sold Separately | Bonnet B-80 (¥ 6,000) Assembly Manual (¥ 2,500) |
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