{"product_id":"audio-research-vt100-mkii-tube-amplifier-serviced","title":"Audio Research VT100 MKII Tube Amplifier - Serviced + New Tubes","description":"\u003cp\u003e\u003cb\u003eGeneral:\u003c\/b\u003e\u003cbr\u003eThe Audio Research VT100 is a classic all-tube power amplifier. Whenever we get one of these in the shop, we're always impressed by its sound. It is also incredibly powerful for an all-tube design, rated at 100 watts into an 8-ohm load.\u003cbr\u003e\u003cbr\u003eThe VT100 is powered by 12 vacuum tubes: eight 6922 tubes in the driver section and four 6550 output tubes. This amplifier has been biased and aligned with a new set of Electro-Harmonix 6922 tubes and a strong matched set of Svetlana Winged C 6550 output tubes. It is sounding beautiful.\u003cbr\u003e\u003cbr\u003eThis particular VT100 is the Mk II version, which features multiple upgrades, including a larger power supply and active cooling. It is also finished in the much harder-to-find black finish.\u003cbr\u003e\u003cbr\u003eAll VT100 amplifiers can be converted to native 220V operation if you have the necessary knowledge. Please let us know when ordering if you'd like it reconfigured.\u003cbr\u003e\u003cbr\u003eThe amplifier is in good condition, with some scratches and signs of normal use. It has been serviced, biased, and is ready to go.\u003cbr\u003e\u003cbr\u003eIncluded with the amplifier are the original box, screwdriver, and owner's manual.\u003cbr\u003e\u003cbr\u003e\u003cb\u003eSkyFi Cosmetic Notes:\u003c\/b\u003e\u003cbr\u003eThis amplifier is in great condition with just some light blemishes on the faceplate. NOTE: The including packaging has a bit of a musty odor but otherwise intact.\u003cbr\u003e\u003cbr\u003e\u003cb\u003eSkyFi Technical Notes:\u003c\/b\u003e\u003cbr\u003eThis is the MKII version of this amp, featuring fan cooling. We also confirmed that a resistor change service bulletin for reducing current in the driver stage had already been implemented. This unit was serviced in house here at SkyFi. We fitted a brand new set of selected Electro Harmonix 6922 tubes in the driver section and aligned the driver circuitry according to Audio Research specification. The output tubes are two strong used matched quads of the legendary Svetlana Winged C 6550. Both channels test to 100W into 8 ohms, both channels driven.\u003cbr\u003e\u003cbr\u003e\u003cb\u003eBrand Background:\u003c\/b\u003e\u003cbr\u003eAudio Research continues its dedication to unparalleled musical expression and crafting components of the highest quality and lasting value for its customers. Our long-term dedication to service is peerless in this industry (Audio Research, with few exceptions, can repair anything ever produced during its entire history). We continue to seek out new and exciting ways to make music more real and more enjoyable. More than just a name or a marketing tool, Audio Research has come to represent exceptional performance and long-term value. Experience Audio Research – experience High Definition®.\u003cbr\u003e\u003cbr\u003e\u003cb\u003eOwnership:\u003c\/b\u003e\u003cbr\u003eSingle Owner\u003cbr\u003e\u003cbr\u003e\u003cb\u003eConnections:\u003c\/b\u003e\u003cbr\u003eRCA + XLR Inputs, Speaker Binding Posts, IEC Power Input\u003cbr\u003e\u003cbr\u003e\u003cb\u003eGeneral Sound:\u003c\/b\u003e\u003cbr\u003eBig beautiful musical sound with little fatigue.\u003cbr\u003e\u003cbr\u003e\u003cb\u003eCosmetic Condition:\u003c\/b\u003e\u003cbr\u003e7\/10 = Good. One or two minor scratches. Well Maintained. See our detailed rating description \u003ca href=\"https:\/\/skyfiaudio.com\/pages\/our-rating-scale\" target=\"_blank\"\u003ehere\u003c\/a\u003e.\u003cbr\u003e\u003cbr\u003e\u003cb\u003eWorking Condition:\u003c\/b\u003e\u003cbr\u003eWorking perfectly and tested in our lab and listening room.\u003cbr\u003e\u003cbr\u003e\u003cb\u003eIncluded:\u003c\/b\u003e\u003cbr\u003eUnit, Box, Manual\u003cbr\u003e\u003cbr\u003e\u003cb\u003ePacking:\u003c\/b\u003e\u003cbr\u003eOriginal Manufacturers Packing\u003cbr\u003e\u003cbr\u003e\u003cb\u003eSpecs:\u003c\/b\u003e\u003cbr\u003ePOWER OUTPUT\u003cbr\u003e100 watts minimum continuous from 20Hz to 20kHz. 1kHz total harmonic distortion typically 1% (VT100 MKIII: 0.3%) at 100 watts, below .05% (VT100 MKIII: 0.03%) at 1 watt. Approximate actual power available at \"clipping\": 110 watts (VT100 MKIII: 120 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.)\u003cbr\u003ePOWER BANDWIDTH\u003cbr\u003e(-3dB points) 15Hz to 80kHz. VT100 MKIII: (-3dB points) 12Hz to 60kHz\u003cbr\u003eFREQUENCY RESPONSE\u003cbr\u003e(-3dB points at 1 watt) 1Hz to 100 kHz. VT100 MKIII: (-3dB points at 1 watt) 1Hz to 80 kHz\u003cbr\u003eINPUT SENSITIVITY\u003cbr\u003e1.9V RMS (Bal or SE) for rated output. (23.5 dB gain into 8 ohms.). VT100 MKIII: 1.7V RMS (Bal, 0.87V RMS SE) for rated output. (24.3 dB Bal gain, 32.2dB SE gain into 8 ohms.)\u003cbr\u003eINPUT IMPEDANCE\u003cbr\u003e200K ohms Balanced, 100K ohms Single-ended.\u003cbr\u003eOUTPUT TAPS\u003cbr\u003e8 ohms, 4 ohms\u003cbr\u003eOUTPUT REGULATION\u003cbr\u003eApproximately 0.8dB 8 ohm load to open circuit\u003cbr\u003eOVERALL NEGATIVE FEEDBACK\u003cbr\u003e10dB. VT100 MKIII: 15dB\u003cbr\u003eDAMPING FACTOR\u003cbr\u003eApproximately 11\u003cbr\u003eDISTORTION\u003cbr\u003e1kHz total harmonic distortion typically 1% at 100 watts, below .05% at 1 watt\u003cbr\u003eSLEW RATE\u003cbr\u003e15 Volts\/µs. VT100 MKIII: 8 Volts\/µs\u003cbr\u003eRISE TIME\u003cbr\u003e3 µs. VT100 MKIII: 4 µs\u003cbr\u003eHUM \u0026amp; NOISE\u003cbr\u003eLess than 0.5mV RMS - 95dB below rated output (IHF weighted, input shorted). VT100 MKIII: Less than 0.2mV RMS - 103dB below rated output (IHF weighted, Bal input shorted)\u003cbr\u003ePOWER SUPPLY ENERGY STORAGE\u003cbr\u003eVT100: 270 joules. VT100 MKII\/III: 540 joules\u003cbr\u003ePOWER REQUIREMENTS\u003cbr\u003e105-125VAC 60Hz (210-250VAC 50Hz) 585 watts at rated output, 750 watts maximum, 380 watts at \"idle\". VT100 MKII\/III: 105-125VAC 60Hz (210-250VAC 50Hz) 650 watts at rated output, 800 watts maximum, 440 watts at \"idle\"\u003cbr\u003eTUBE COMPLEMENT\u003cbr\u003eVT100: (4 matched pairs) 6550 power output, (8) 6922. VT100 MKII: (4 matched pairs) 6550C power output, (4) 6922 driver, (4) 6922 input. VT100 MKIII: (4 matched pairs) 6550C power output, (4) 6H30 driver\u003cbr\u003e\u003cbr\u003e\u003cb\u003eDimensions:\u003c\/b\u003e\u003cbr\u003e19\" (48.3 cm) W x 8 ¾\" (22.2 cm) H x 19½\" (49.5 cm) D. Handles extend 1½\" (3.8 cm) forward\u003cbr\u003e\u003cbr\u003e\u003cb\u003eWeight:\u003c\/b\u003e\u003cbr\u003e66.7 lbs.\u003cbr\u003e\u003cbr\u003e\u003cb\u003eApproximate Age:\u003c\/b\u003e\u003cbr\u003e1998\u003cbr\u003e\u003cbr\u003e\u003cb\u003eLink to Manual:\u003c\/b\u003e\u003cbr\u003e\u003ca href=\"https:\/\/audioresearch.com\/new_website\/wp-content\/uploads\/2024\/11\/VT100II_Manual.pdf\" target=\"_blank\"\u003eClick Here\u003c\/a\u003e\u003cbr\u003e\u003cbr\u003e\u003cb\u003eRecommended Cables:\u003c\/b\u003e\u003cbr\u003e\u003ca href=\"https:\/\/skyfiaudio.com\/products\/kimber-kable-hero-interconnects-pair-rca-ultraplate-or-wbt-connectors-new\" rel=\"noopener\" target=\"_blank\"\u003eKimber Kable - RCA Interconnects\u003c\/a\u003e - Better\u003cbr\u003e\u003cbr\u003e\u003ca href=\"https:\/\/skyfiaudio.com\/products\/kimber-kable-silver-streak-interconnects-pair-rca-ultraplate-or-wbt-connectors\" rel=\"noopener\" target=\"_blank\"\u003eKimber Kable - RCA Interconnects\u003c\/a\u003e - Best\u003cbr\u003e\u003cbr\u003e\u003ca href=\"https:\/\/skyfiaudio.com\/collections\/our-kimber-kable-collection\/products\/kimber-kable-ascent-series-hero-analog-interconnects-pair-balanced-xlr-connectors-new\" rel=\"noopener\" target=\"_blank\"\u003eKimber Kable - BALANCED XLR Connectors\u003c\/a\u003e - Better\u003cbr\u003e\u003cbr\u003e\u003ca href=\"https:\/\/skyfiaudio.com\/collections\/our-kimber-kable-collection\/products\/kimber-kable-summit-series-silver-streak-analog-interconnects-pair-balanced-xlr-connectors-new\" rel=\"noopener\" target=\"_blank\"\u003eKimber Kable - BALANCED XLR Connectors\u003c\/a\u003e - Best\u003cbr\u003e\u003cbr\u003e\u003ca href=\"https:\/\/skyfiaudio.com\/products\/kimber-kable-8tc-8-tc-ascent-speaker-cables-pair-new\" rel=\"noopener\" target=\"_blank\"\u003eKimber Kable - Speaker Cables\u003c\/a\u003e - Better\u003cbr\u003e\u003cbr\u003e\u003ca href=\"https:\/\/skyfiaudio.com\/products\/kimber-kable-pk14-pk-14-ascent-power-cord-brand-new\" rel=\"noopener\" target=\"_blank\"\u003eKimber Kable - Power Cords\u003c\/a\u003e - Better\u003cbr\u003e\u003cbr\u003e\u003ca href=\"https:\/\/skyfiaudio.com\/products\/kimber-kable-ascent-series-pk10-pk-10-power-cord-brand-new\" rel=\"noopener\" target=\"_blank\"\u003eKimber Kable - Power Cords\u003c\/a\u003e - Best\u003cbr\u003e\u003cbr\u003e\u003cb\u003eTesting Process:\u003c\/b\u003e\u003cbr\u003eWe 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. \u003cbr\u003e\u003cbr\u003eIf the amplifier passes visual inspection, we move on to a full test of all of the tubes. We use a modern Amplitrex AT-1000 Professional Tube Tester which is capable of testing both emission and Gm with a high degree of accuracy. \u003cbr\u003e\u003cbr\u003eWe document the results of each tube and replace any weak or suspect tubes before proceeding. \u003cbr\u003e\u003cbr\u003eWhen 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.\u003cbr\u003e\u003cbr\u003eIf 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.\u003cbr\u003e\u003cbr\u003eOnce we have verified that the amplifier is safe to operate, we connected it to full mains power. For fixed bias amps we set the bias to manufacturer spec. 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. \u003cbr\u003e\u003cbr\u003eWe start by feeding the input of the amplifier with a low level 1 KHz test signal, slowly increasing 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.\u003cbr\u003e\u003cbr\u003eWe finish off the bench evaluation with a 1 KHz square wave check and a 20 Hz to 20 KHz 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. \u003cbr\u003e\u003cbr\u003eBefore 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. \u003cbr\u003e\u003cbr\u003eIf 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 minimum. \u003cbr\u003e\u003cbr\u003eFor tube amps we like to run this test at least twice.\u003cbr\u003e\u003cbr\u003eThis 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.\u003c\/p\u003e","brand":"Audio Research","offers":[{"title":"Default Title","offer_id":48561027776766,"sku":"107785","price":3990.0,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0003\/3275\/9084\/files\/fHqRP5K3uIZAk4TUsiAj8qL4NZzJdL2aOX6-d5Q2tUY.jpg?v=1783616493","url":"https:\/\/skyfiaudio.com\/products\/audio-research-vt100-mkii-tube-amplifier-serviced","provider":"SkyFi Audio","version":"1.0","type":"link"}