Audio Database

KMQ60
Commentary

Stereo power amplifier kit using the same parts as MQ60 model.

The circuit configuration follows MQ60 and is based on the power amplifier of SQ38FD and SQ38FD/II.

The output tube uses 50CA10, a medium-sized triode. 50CA10 is a compact Ron-type vacuum tube with low internal resistance and excellent bare characteristics.
The output transformer uses the OY15 type, which is used in Lux's SQ38FD/II.

A cathode coupled type is used for the drive stage.
The cathode-coupled circuit is based on the Mulard type and has been improved to take advantage of the characteristics of the circuit. This circuit features a direct connection between the voltage amplification stage at the first stage and the phase inversion stage at the next stage. The time constant circuit is small for the number of stages, and the loop gain of the amplifier can be large.
In the original circuit of the Mulard, 6267 is adopted for the voltage amplification stage of the first stage, and this is used as a 5-pole tube. However, in the KMQ60, the same 6267 is adopted for the first stage, and it is connected to a 3-pole tube to lower the internal resistance and improve the high-frequency distortion characteristics.

Since the total gain is insufficient in the configuration of the drive stage adopted for the KMQ60, a High Gm twin triode 6AQ8 is used in the phase inversion stage to gain gain in this stage, making it easier to maintain AC balance and to suppress distortion in the first stage.

All stages are composed of 3-pole tubes (the first stage consists of 3 connections of 6267), which improves the bare characteristics and ensures high stability by only applying a small amount of NF.

A resistor (22 Ω) and a capacitor (0.22 μ F) are connected in series to the secondary side of the output transformer.
This circuit is designed to prevent the amplifier from becoming unstable due to almost no load in the high frequency range where the impedance of the speaker increases. It is a kind of integral phase compensation circuit.
In addition, a buffer resistor is inserted into the first stage grid in order to avoid the effect of impedance from the output of the control amplifier, etc., and consideration is taken to suppress the fluctuation of frequency characteristics caused by volume change.

The hood in the picture was sold as an option sold separately.

Initially the panel design (logo) seems to be slightly different.

Model Rating
Type Bulb type power amplifier kit
Continuous output 30W + 30W (4 ω, 8 ω, 16 ω)
Total harmonic distortion factor Within 0.7% (at Rated Output)
0.5% or Less (at 1 khz, 30W output, 1975 catalog)
1% or Less (55 Hz, 10 kHz, 30w output, 1975 catalog)
Frequency characteristic 15 Hz to 60 kHz - within 1 dB
20 Hz to 20 kHz - within 1 dB (1975 Catalog)
Signal-to-noise ratio 90 dB or more
Residual noise 0.7 mV or less
Damping factor Approximately 15 (1 kHz)
Input sensitivity 850 mv (at rated output)
750 mv (1975 Catalog)
Input impedance 250k Ω
Load impedance 4 Ω, 8 Ω, 16 Ω (switch switching)
Vacuum tube used 50CA10x4
6DT8/6AW8/6AQ8x2
6267x2
Semiconductor used DA16Ax4 (DS-16Ax1 in 1975 catalog)
DS16Cx1 (SD-1Bx4 in 1975 catalog)
Power consumption 160W
External dimensions Width 410x Height 160x Depth 205 mm
Weight 13.8kg
Sold Separately Bonnet B-60 (¥ 4,500)
Assembly Manual (¥ 500)