VTL MB-175 Signature

 

SOLD  $7,500.00

JAN 2009

 

  • Mint Condition

  • Made In U.S.A.

  • Original Boxes/Manual

  • Worldwide Shipping

Stereophile Review

Manufacturer's Homepage

 

The 175, though not designed by the senior Manley, is based on the basic circuit guidelines outlined in his book on tube design, The Vacuum Tube Logic Book. The power supply features a solid-state rectifier bridge and a pair of 3800µF caps—meat'n'potatoes stuff. The power tubes are more unusual: 807s—inexpensive, relatively low-power radio transmitter devices (no longer in use for that purpose) that feature ultra-wideband response said to reach from above 125MHz down to DC. Using the 807s (similar to KT66s, according to Manley's book) as power tubes is tricky, because their wide bandwidth makes them prone to oscillation, but using 807s would be the "push-pull answer to the sound of a single-ended amp." The tube is a five-pin, classic Coke-bottle-shaped device complete with anode cap.

The design uses a modest 6dB of negative feedback and is switchable between triode and tetrode modes. Claimed frequency response is 20Hz-20kHz, and a low 1.5% THD at full-rated 175W output into 4 ohms.
Manley told me that average tube life is a relatively high 2500 hours, in part due to the design's low 30mA current draw. Combine that with the 807's low cost and you have, theoretically, a low-maintenance, high-performance amp t, including the 12AT7 and 6350 input tubes (dual triode drive and phase splitter, respectively). Given the long tube life, re-tubing should be necessary only once every four or five years, with average use.

The key to getting high-quality performance and sound from any tube amplifier is its output transformer. The Signature 175 uses VTL's newly developed, highest-quality, and most expensive "Signature" transformer, which has been precisely matched to the plate impedance of the output tube for greater efficiency. Manley told me that the tight, carefully layered windings of each section result in "smooth sound" and "very clean square wave response."
 

Specifications

Description: Vacuum-tube monoblock amplifier. Output power (20Hz-20kHz into 4 ohms): 175W (19.4dBW) (tetrode), 90W (16.5dBW) (triode). THD (20Hz-20kHz at maximum power): <3%, tetrode or triode mode. S/N ratio: 106dB (tetrode, 120Hz); 108dB (triode, 120Hz). Input sensitivity (for full output): 1V. Input impedance: 130k ohms. Load impedance: 3-8 ohms.

Power consumption: 160W idle, 380W full power.


Dimensions: 19" W by 8.5" H by 10" D. Weight: 50 lbs.

Price: US$4990/pair.


Manufacturer: Vacuum Tube Logic, 4774 Murietta Street, Suite 10, Chino, CA 91710. Tel: (909) 627-5944. Fax: (909) 627-6988. Web site: www.vtl.com