SkyFi Audio – Curators of Vintage Audio Gear. No mid-fi, no gimmicks, no junk. Each piece of equipment is cosmetically restored and fully tested in our well-equipped lab by an engineer with 30+ years of experience in the HiFi world. Through our sister company, which is an authorized dealer for McIntosh, Audio Research, Sonus Faber, ClearAudio, Project, and Sony ES, we have access to OEM parts, service, and support. We are big fans of the VT100 variation which we have a hard time keeping in stock. This is its larger brother VT200 MKI at twice the power, but with the same design and build quality. This is a very powerful tube amp capable of driving difficult loads with the same neutral and clear sound that you would expect from Audio Research. It has facilities for balanced and single ended operation and offers speaker connections from 1 ohm to 16 ohms. Serviced in house and working beautifully. Little to no signs of use cosmetically. Includes a custom dust cover (for when the amp is not in use obviously), and the manual. SkyFi Service Notes. All driver tubes replaced. Front end adjustments and bias set to service manual specification. Tube Notes. All driver tubes replaced with matched balanced JJ E88CC. All output tubes are pre-owned matched quads of Svetlana 6550 ribbed plate (Not Winged C). The SkyFi Testing Process for Tube Amplifiers. We start with a visual inspection of all internal components to make sure that there are no signs of heat stress or damage. Capacitors are checked for telltale signs of predictive failure including bulging, shrunken wrappers, or physical leakage. We also inspect resistors and other passive components for signs of overheating. If tube arcing has occurred in the past we can usually spot discoloration on the output tube sockets. On vintage units we often spot check select capacitors for value and ESR. If the amplifier passes visual inspection, we move on to a full test of all of the tubes. We use an Amplitrex AT-1000 Tube Tester which is capable of testing both emission and Gm with a high degree of accuracy. We document the results of each tube and replace any weak or suspect tubes before proceeding. When we power on tube amplifiers for the first time we usually use a variac and current limited AC supply and slowly raise the voltage up to nominal mains level while monitoring plate, screen, filament, and negative bias supply voltages where applicable. If everything is in order we feed a low level test signal into the amplifier’s input and monitor its output on an oscilloscope across an 8 ohm dummy load. At this point we are just looking to verify basic function and confirm that the output transformers are not damaged. Once we have verified that the amplifier is safe to operate, we connected it to full mains power. For cathode biased amps we monitor the plate to cathode voltage to determine if the output tubes are operating in a safe range. Once the output section is verified we move onto bench evaluation. We start by feeding the input of the amplifier with a low level 1KHz test signal, slowly increase its amplitude while monitoring the amplifier’s output on an oscilloscope for signs of noise, clipping, distortion, or improper channel balance. We continue increasing the signal level until the amplifier reaches clipping. At this point we take an output power measurement and compare it to the spec sheet of the amplifier to verify proper performance. We finish off the bench evaluation with a 1KHz square wave check and a 20Hz to 20KHz sine sweep to assess the amplifier’s frequency response characteristics. This battery of tests will usually reveal if the amplifier has any issues that need further attention. Before the device leaves the bench, we perform a listening test with actual music using a variety of preferred test tracks. Our benches are outfitted with familiar monitor speakers which help us identify inconsistencies that will not always show up on our test gear. The main things that we are listening for are hum or noise with no signal present, proper center image, clicks, pops, or any other obvious undesirable audio characteristics. If the unit passes all of these tests it is moved to our long term testing rig where we simulate real word operating conditions for 6-8 hours. For tube amps we like to run this test at least twice. This allows us to monitor the unit for signs of thermal runaway or intermittent issues that only crop up when it has fully come up to temperature. We find this step to be essential, especially for vintage units. More from Audio Research: The VT200 vacuum tube stereo power amplifier is the most powerful of the three VT-series models. Rated at 200 watts per channel into a wide range of speaker loads, the VT200 encompasses a “dual mono” circuit layout reaching back to the massive single power transformer. Eight matched pair of 6650C output tubes and 674 joules of distributed energy storage give the VT200 unwavering control over the most difficult speaker loads, without sacrificing dynamic freedom or musical nuance. Separate left and right input and output circuit boards, with distributed power supplies, keep signal path lengths at a minimum for quicker transient attack and explosive musical dynamics. As with other VT models, constant-current sources in the input stage help maintain stable drive characteristics and differential balance of the output stage under the rapidly changing demands of actual music reproduction. Ultralinear output transformers with partial cathode coupling to the output terminals give the VT200 higher efficiency and lower output impedance than conventional vacuum-tube amplifiers. This results in better control of the loudspeaker throughout its frequency and impedance spectrum. Both single-ended (100K ohms) and balanced (200K ohms) inputs are included to allow use with any high-quality stereo preamplifier. Custom-machined, gold-over-brass five-way output terminals allow a secure, high-contact connection to a variety of speaker impedances: 1, 2, 4, 8 or 16 ohms. Internally, the VT200 presents a very open architecture within a spacious, rugged chassis. A single cooling fan operable at three different speeds provides unobstrusive cooling of interior components, including the vacuum tubes mounted along the chassis sidewalls. Biasing of the output tubes is easily accomplished via two trim pots for each channel, accessible through holes located along each sidewall of the chassis. Complete retubing kits of tested, selected and matched tubes for the VT200 are available through authorized Audio Research dealers, or from the factory. DETAILS and SPECIFICATIONS – MKI Tube stereo amplifier. 200 watts per channel continuous from 20Hz to 20kHz. 1kHz total harmonic distortion typically 1% at 200 watts, below. 01% at 1 watt. Approximate actual power available at “clipping”:210 watts (1kHz) Note that the actual RMS power output is dependent upon both line voltage and “condition” ie: if power line has high distortion, maximum power will be affected adversely, although from a listening standpoint this is not very critical. (-3dB points) 12Hz to 120kHz. (-3dB points at 1 watt) 0.5Hz to 200 kHz. 2.5V RMS (Bal or SE) for rated output. (27 dB gain into 16 ohms). 200K ohms Balanced, 100K ohms Single-ended. 1, 2, 4, 8, 16 ohms. Approximately 0.8dB 16 ohm load to open circuit. Less than 0.2mV RMS – 109dB below rated output (IHF weighted, input shorted, 16 ohm output). POWER SUPPLY ENERGY STORAGE. 105-125VAC 60Hz (210-250VAC 50Hz) 990 watts at rated output, 1200 watts maximum, 680 watts at “idle”. VT200: (8 matched pairs) 6550C power output, (6) 6922 driver, (4) 6922 input. 19″ (48.3 cm) W x 10½” (26.7 cm) H x 23.6 (60.0 cm) D. Handles extend 1½ (3.8 cm) forward. (46.5 kg) Net; 148 lbs. Yes – Power Only. We have too many items for sale and it is nearly impossible to keep track of offers outside of the official system. We are currently operating from our shop inside our dedicated building in Glen Rock, NJ. We’re not a store, so please don’t make an appointment if you’re just curious as to how a speaker or piece of equipment sounds. In essence – no tire kickers please. This is super useful when purchasing large speakers or heavy amplifiers. It’s also great for ensuring your new turntable is setup correctly in its final resting place. This item is in the category “Consumer Electronics\Vintage Electronics\Vintage Audio & Video\Vintage Amplifiers & Tube Amps”. The seller is “skyfiaudio” and is located in this country: US. This item can be shipped to United States.
- Brand: Audio Research
- Type: Tube Amplifier
- MPN: VT200 MKI
- Model: VT200 MKI
- Country/Region of Manufacture: United States
