Audio Hungary APX 200 Tube Power Amplifier

APX 200

As the successor of the former amp BEAG APX 100, we have created the vacuum tube stereo power amp Qualiton APX 200 which is able to operate low impedance speakers. As opposed to the previous model, in the case of the Qualiton APX 200 we did not insist on the monoblock design. Instead, we regarded it as more favourable if we used a more compact and economical stereo version compared to the previous design.

The power of the appliance was set as 2 x 100 W, consequently it is able to dynamically operate even more insensitive speakers. The frequency response of the power amp is fully linear in the audio-frequency range, at nominal, i.e. 100 W output power, measured with sinusoidal waveform. The low frequency breakpoint of the frequency response is 15 Hz, the upper cutoff frequency is 100 kHz (-3 dB points). In the entire audio-frequency range, the total harmonic distortion is less than 1% and the signal-to-noise ratio of the appliance is typically higher than 101 dB. While developing this product, the listed technical parameters were attained due to carefully designed circuit arrangements, a selected set of vacuum tubes and an accurately dimensioned and a manufactured output transformer.

The protection of the vacuum tube set is handled with special care. The lifespan of the tubes can be drastically reduced by uncontrolled transient surges of current at the moment of power-on. Similarly, suddenly switching high anode voltage on non-preheated vacuum tubes can have an adverse effect on the lifespan. In order to eliminate those effects, the appliance is equipped with a slow-start circuit and an anode voltage delay circuit.  

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