Усилители мощности моно — NAT Transmitter EVO

The Transmitter EVO is a single-ended valve monoblock from NAT Audio, the Serbian company that has built amplifiers of this kind since the 1990s. This is the newest Transmitter and uses a large transmitting valve, the Philips QB5/1750, triode-connected, in the output stage. NAT describes it as the best Transmitter to date.

Key specs that matter

Output per monoblock is up to 80 W in high-power mode and 40 W in low-power mode, in single-ended pure Class A. Frequency response is 8 Hz to 60 kHz, and signal-to-noise is 110 dB. The amplifier drives speakers from 2 ohms to over 16 ohms. The driver and input valves are NOS military-grade 6N6P. Inputs are gold-plated PTFE-insulated RCA. The front panel is a 15 mm quadruple aluminium plate. Each monoblock measures 360 x 640 x 310 mm and weighs 40 kg.

Engineering and use context

The QB5/1750 can dissipate up to 565 W, and the Transmitter EVO uses only about 35% of that, lowering its operating temperature for reliability. The valve, also known as the Siemens RS687, is a power tetrode, and its sturdy mechanical construction makes it free of microphonics. The low-power mode reduces output to 40 W for sensitive speakers and further lowers the dissipation and heat of the output valve. The circuit is direct-coupled from input to output transformer, with no coupling capacitors or interstage transformers in the signal path, a topology NAT has used since the 1990s. There is zero global feedback. The output transformer is a wide-bandwidth design made to NAT's specification. The power supply is sized at twice the power the amplifier draws at full output, and all stages, including the output stage, have regulated high-voltage and filament supplies, supported by additional polypropylene capacitors. An automatic bias circuit controls the output valve's current, so no adjustment is needed. A soft start protects the valves at switch-on. The chassis is modular and hand assembled, CNC machined, and a stainless steel cover cage improves vibration isolation. Speaker connectors are laboratory grade.

Pairing

With its unusually high single-ended power and wide load tolerance, a pair of Transmitter EVO drives a wider choice of speakers than most single-ended amplifiers. NAT's Magnetostat SE preamplifier was used with it at shows.

Alternatives

NAT's Magma EVO is the larger single-ended monoblock of the brand with the GM100 triode and 170 W.