Усилители мощности стерео — VTL ST-150

The ST-150 from VTL is a two-channel tube power amplifier belonging to the Performance series, entirely hand built by the company's craftsmen and made to order with around three months of lead time. VTL describes it as its high value, high power stereo tube design, placed in one compact chassis.

Key specs that matter

Rated output is specified into a 5 ohm load from 20 Hz to 20 kHz at less than 3 percent THD, and the amplifier works with loads between 2 and 8 ohm. Input impedance is 130 kilohm. Input sensitivity for full output depends on the mains version, at 0.880 V for 100 V units and 1.0 V for 120 and 240 V units. The signal to noise ratio is -95 dB at 120 Hz. The ST-150 draws 240 W from the wall when idling and 800 W at full power. The mains fuse is a 15 A slow-blow ceramic type for 100 and 120 V supplies and 8 A for 220 or 240 V, and the B+ rail is protected by a 1 A fast-acting ceramic 600 V fuse. The chassis is 48 cm wide, 30 cm deep and 23 cm high, and it weighs 38.6 kg bare or 50 kg packed for shipping.

Engineering and use context

Eight 6550 output tubes do the work, four per channel, with each tube given its own bias setting. A parallel 12AT7 input stage and a 12BH7 long-tailed phase splitter drive the push-pull output stage, using two of each small-signal type. The power supply has an energy storage capacity above 200 joules, and the output transformers are a VTL proprietary design. A dedicated grounding scheme keeps the noise floor very low, and the signal path uses film and foil capacitors of audiophile grade. Tetrode or triode operation is selected by switch, so one chassis offers two output configurations. The front panel is extruded aluminium and comes in black or silver.

Pairing

VTL states that the ST-150 suits smaller electrostatic panels and dynamic loudspeakers that do not demand high current. In triode mode the maker advises speakers with a sensitivity of 92 dB at 1 W and 1 m or higher. The 130 kilohm single-ended input is easy to drive from a tube preamplifier, and VTL builds the TL-5.5 Series II Signature in its own Signature range for that role. Since the amplifier sits on a single chassis, one pair of loudspeaker cables runs from one location.

Alternatives

The VTL S-200 Signature is a stereo valve amplifier from the Signature range with 200 W per channel in tetrode, a fully balanced circuit and SmartTube automatic biasing.