McIntosh MA230 Tube Integrated Amplifier SKYFI RESTORED

  

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. This is a super clean MA230 vintage integrated amplifier from McIntosh, arguably the best sounding and most coveted tube integrated from the brand. This example underwent a lengthy in-house restoration where it was brought up to factory-like performance to ensure long term reliability. This is a highly collectible piece and pristine examples like these are increasing in value every year.

McIntosh did not make many tube integrated models, making this a collectors piece from the late 1960's and one of the most sought after tube integrated amps from McIntosh. Cosmetically it's super clean and presents beautifully with shiny chrome and great paintwork. The faceplate is also super clean with little signs of use.

The top graphics plate has faded to a vintage light brown which looks retro-cool. Best of all it's currently fitted with factory McIntosh output tubes and vintage Telefunken driver tubes for that perfect vintage sound. The MA230 integrated combines a solid state preamp with a tube power amplifier rated at 30W. Capable of driving most vintage speakers AND a great value since it has a capable built-in phono stage. On the front you'll find the usual controls plus two settings for phono input (RIAA and LF), phase 0-180, low and high frequency filters, and loudness.

Simply select the option in this listing to add. SkyFi Restoration Notes: McIntosh chose very high quality film coupling capacitors for the signal path which hold up very well over the years. For this reason our in-house restoration was almost exclusively focused on the power supplies of the MA230. When this MA230 arrived at our shop it was not working properly.

Two of the multi-section cans were way out of spec and needed replacement. To keep the look of the unit original, we opted for a full set of new production replica multi-section can capacitors. This keeps the wiring true to the original layout so that everything looks original with the bottom cover removed. In addition to the mutli-section cans, we replaced all of the drifted axial electrolytic capacitors and freshened up the diodes in the B+, negative bias, and regulated solid state preamp supplies.

All tubes were tested in our modern and professional Amplitrex AT1000, with output tube bias set to official McIntosh service manual spec. This MA230 passed our bench and listening tests with flying colors and really is a joy to listen to. SkyFi Tube Notes: 2 x Telefunken 12AU7 2 x Telefunken 12AX7 4 x McIntosh Branded American Made 7591. Hybrid (solid state preamp and tube power amplifier). Response 20-20kHz (+0 -0.5dB). Noise and hum -75dB high level, -60dB low level. Output impedance 4, 8 and 16 ohms. Input sensitivity and impedance: high level 0.25V at 250k, phono 1.5mV at 47k, tape head 1.5mV at 1 meg. Tape output 0.25V into 25k.

L+R output 10V into 5k. Dual concentric tone controls +18dB to -18dB.

LF filter 50Hz at 12dB/oct. HF filter 5k at 12dB/oct. FRONT PANEL: Glass panel at top. Input selector: aux, tape, tuner, phono 1, phono 2 and tape hd. Bass and treble each dual concentric. Mode selector: L to L+R, R to L+R, stereo rev, stereo, mono (L+R), L+R to L and L+R to R. Rocker switches: comp: RIAA or LP, tape monitor, phase: 0 or 180, speaker: on or off, power: on or off, LF: flat or filter, HF: flat or filter, loudness: flat or compensate. BACK PANEL: Barrier strips for 4, 8, and 16 ohms, Outputs: Tape and L+R. High level inputs: tape mon, aux, tape and tuner. Low level inputs: ph 1, ph 2 and tape hd. AC outlets: 2 switched, 1 unswitched. Size 5-7/16"H, 16"W and 14-1/2D. The SkyFi Testing Process for Preamplifiers. 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 the PCBs for discoloration from resistors or transistors that may have been running hot.

On vintage units we often spot check select capacitors for value and ESR. When we first power on a preamplifier we connect its RCA output to a Sencore PA81 Power Analyzer which simulates real world loading conditions and gives us an oscilloscope interface. The first order of business is checking that the volume control works smoothly throughout its entire range with acceptable channel balance.

This is accomplished by feeding a 1KHz sine wave into one of the preamp's line level inputs while monitoring the preamp's output on an oscilloscope. We then switch to a 1KHz square wave to test the tone controls, loudness function, and filters where applicable. During this step we are watching for equal alteration of the test signal by both channels.

This also helps us identify dirty controls that will need treatment. Once the basic line stage functions are verified, we test each input individually. This is especially important for devices that use relays to select their sources. If the preamp is equipped with a phono stage we test that as well.

We use an inverse RIAA filter which allows us to feed a reference test signal into the phono input with the proper RIAA equalization and level. A square wave or sine sweep is used to verify that the device's phono stage is faithfully reproducing the RIAA curve.

If the preamp under test has balanced inputs and/or outputs these are tested as well. We finish up our bench testing with a listening test with our bench amplifier and reference speakers. During this test we check for hum or hiss that may not have shown up in earlier testing. We also check that all of the tone controls and filters perform as expected. If the preamplifier has remote control functions these are also tested.

Preamps with tube circuits or complicated power supply topologies are connected at our long term test rig for extended stress testing under real world conditions. 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. 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. 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. We have too many items for sale and it is nearly impossible to keep track of offers outside of the official system. Please understand the have no control over this. 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, Canada.

• Brand: McIntosh
• Type: Integrated Amplifier
• MPN: MA230
• Model: MA230
• Country/Region of Manufacture: United States