Allnic Audio A-2000 mkIII Stereo Effektforstærker

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The A-2000 MK3 is a class AB power amplifier that uses two KT170 beam-tetrode output tubes per channel and produces 120W in pentode mode and 60W in triode mode through push-pull operation. One triple-connected 5654 pentode tube per channel is used in the first-stage to secure a voltage gain of 26dB, and two 6S4 triode tubes per channel are used as the phase inversion and drive tubes for push-pull driving of the KT170 output tubes. The A-2000 MK3 uses two of Allnic’ssignature permalloy core output transformers, one per channel.

The front panel design of the A-2000 MK3 has changed significantly from its predecessor’s, and most importantly, the output tubes have changed from the KT150 to the KT170. The KT170 has a different shape and is larger than the KT150, and the KT170’s plate loss, which is used to measure the output, has increased from 70W to 85W. Normally, as a vacuum tube gets bigger, capacitance also increases and the accuracy of the high frequencies declines; however, the design of the KT170 overcomes this weakness, and its operation is very stable.

The 6S4 drive tube is also worth noting. In the original and 25th anniversary models, the E282F pentode was used in a triple connection, but in the SE and now in this new MK3 model, it has beenreplaced bythe6S4 triode. The 6S4 has an internal resistance of 3.7㏀, a voltage amplification factor (mu) of 16, and a current amplification factor (gm) of 4.5mA/V, making it ideal for use as a drive tube. In addition, its plate loss is high at 7.5W, so it has the advantage of being able to drive the KT170 output tube powerfully. After changing to the 6S4 triode, the amplifier became more stable and naturally musical sounding compared to the triple-connected pentode.

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SPECIFICATIONS FOR THE ALLNIC AUDIO A-2000 MK3 KT170 STEREO POWER AMPLIFIER
• Output Power: • 120w (8? load, at 1KHz) Pentode
• 60w (8? load, at 1KHz) Triode
• Distortion: • 0.17% at 1KHz at 10w
• Frequency Response: • 20Hz - 20KHz Flat
• S/N Ratio: • -80dB (CCIR, 1KHz)
• Damping Factor: • 8 at 8? load at 1KHz
• Voltage gain: • +26dB
• Input Impedance: • 100K? (single-ended, unbalanced)
• Input Sensitivity: • 1.3V for maximum rated power
• Fuses: Mains:
AC 5A, 250V slow-blow for 110/120V regions
AC 3A, 250V slow-blow for 230/240V regions
KT170: 0.5A, 250V, 20mm slow-blow
• Tubes (per chassis): • KT170 x 4 (power tube)
• 6S4 x 4 (or 6S4A - second stage drivers)
• 5654 x 2 (first stage, equivalent to EF905 and
CV4010)
• Dimensions: • (W x D x H) 440mm (17 inches) x 480mm (19 inches) X 300mm (12 inches)
• Weight: • 36Kg (80 lbs) net