Power Amplifier Air Tight ATM-3211

Air Tight ATM-3211 — monoblock power amplifiers featuring a 211 triode in a push-pull configuration

The ATM-3211 is a monoblock valve power amplifier based on a directly heated high-voltage 211 triode, configured in a push-pull arrangement. It is the result of five years’ development by Air Tight, and its aim was to preserve the character of triode sound even at power outputs exceeding 100 W per channel. It is precisely this power reserve that enables it to drive even low-efficiency loudspeaker systems with ease – systems that are often beyond the capabilities of simple triode designs.

The signal path is entirely valve-based and comprises three stages: an input differential circuit with a 12AX7, a driver stage with a 12BH7, and a parallel cathode follower using a 12BH7, which ensures sufficient current drive potential for the grids of the power triodes. The amplifier operates in pure Class A up to 30 W and switches to Class AB above this threshold, thereby combining linearity at normal listening levels with power reserve for dynamic peaks.

A key role is played by the massive Tamura output transformers, which define the frequency response in the 10 Hz – 50 kHz band (±1 dB), and the dual-section power transformers, which isolate the power supplies for the individual sections. This design reduces mutual interference between circuits and ensures an immediate supply of power during sudden changes in load. The internal wiring is hand-wired using the point-to-point method, including hand soldering, which shortens signal paths and minimises the number of intermediate connections.

In terms of sound reproduction, the combination of the 211 triode’s linearity, high-quality output transformers and a stable power supply results in the clarity of fine details in pianissimo passages, precise localisation of instruments and dynamic range in fortissimo without audible saturation. Mechanical stability is complemented by a hand-finished 15 mm-thick aluminium front panel and WBT speaker terminals with low contact resistance.

Key features

• Power: Push-pull 211 triode with output exceeding 100 W
• Class: Pure Class A up to 30 W, Class AB above that
• Circuits: Differential 12AX7 and parallel cathode follower 12BH7
• Transformers: Tamura output transformers and dual-stage power transformers
• Construction: Hand-wired point-to-point, WBT terminals