McIntosh MAC1500 Receiver - The Best Tube Receiver Ever? SkyFi Restored

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General:
Arguably the best tubed receiver ever made (some will argue Fisher takes this honor) but definitely the best one McIntosh ever produced.

Our first and only MAC1500 listing. Produced for only two years (1965 - 1967), we searched for a long time to find the right MAC1500 candidate for restoration. They're not something you come across often to begin with, and the few that survived the past 59 years are usually in sad condition with many missing bits and pieces.

The tube amplifier section is similar to the renowned McIntosh MC225 which we vote the best amp from this brand. The MC225 is also considered by many to be the best tube amplifier ever manufactured. 

The tube tuner section is similar to the McIntosh MR67, considered by many to be among the best tube tuners ever made.

The preamp section is another great McIntosh component.

While the word best evokes strong emotions among audiophiles, knowledgeable audio experts and technicians agree that the quality of this handmade beauty is unparalleled.

McIntosh tube gear from this era was handmade and is famous for being gentle on the tubes, leading to incredibly long tube life.

Another interesting feature is the headphone section of this receiver which has a separate, specialized winding designed for using high-end headphones. This feature exists in no other receiver I can find in the literature (borrowed from an eBay listing).

The McIntosh MAC1500, introduced in 1965, is essentially a hybrid amplifier with a solid state preamp section, tube output section, and tube FM tuner. It's a fairly rare piece of equipment as only around 2634 units were made for domestic US use only.

McIntosh later produced the MAC1700 which featured a solid state preamp and output sections and tube tuner. The later MAC1900 became a full solid state unit.

The MAC1500 puts out 30 watts per channel and is also known for having one of the better headphone sections of any receiver. It apparently has special secondary transformer windings specifically for the headphone output, as opposed to the usual resistor placed in the speaker output circuit.

SkyFi Restoration Notes:
• Multi-section capacitors replaced with custom reproduction parts.
• 9 ohm power supply resistor replaced with higher wattage part.
• All diodes replaced.
• Heat stressed bias resistors replaced.
• All axial electrolytic capacitors replaced.
• All McIntosh service manual audio adjustments completed.
• Tuner aligned.
• Dial lamps and stereo lamp filter replaced.
• Re-tubed as needed.
• Output tube biased to 0.7V as outlined in the service manual.
• Both channels tested to 30W into 8 ohms before clipping.

SkyFi Tube Notes:
• Tuner tubes: Mix of original McIntosh silkscreened tubes with strong testing vintage and modern production tubes.
• Tube driver circuitry: Balanced Sovtek 12AX7 and (2) Philips JAN 6189W.
• The four output tubes were replaced with a modern production matched quad set of Tung Sol 7591.

SkyFi Cosmetic Notes:
• Minor blemishes in glass dial and front glass.
• A few light marks are present in the top metal area and top of the faceplate frame
• RCA Jacks show wear. We found these jacks have a smaller than usual diameter, so a good quality (tight-fitting) interconnect should be used for best performance.
• Speaker terminal blocks are fully intact.
• Wood cabinet has a couple of minor blemishes.

Brand Background:
McIntosh Laboratory is an American manufacturer of handcrafted high-end audio equipment based in Binghamton, New York. The company was founded in 1949 by Frank McIntosh. The company designs and produces audio amplifiers, stereo tuners and other consumer electronics products.

Ownership:
Single Owner

Connections:
RCA inputs, screw terminals for speakers and antenna. 3 convenience outlets.

General Sound:
Neutral sound with little to no coloration

Cosmetic Condition:
7/10 = Good. One or two minor scratches. Well Maintained.. See our detailed rating description here.

Working Condition:
Working perfectly and tested in our lab and listening room.

Included:
Just the unit and power cord.

Packing:
Original Manufacturers Packing

Original MSRP:
$499.00 in 1965. Close to $5000 today after adjusting for inflation.

Dimensions:
16" x 5.5" x 16"

Weight:
40 lbs.

Approximate Age:
1966

Link to Manual:
Click Here

Specs:
Please see our photos of or the linked manual above for complete specifications.

The MAC1500 uses the following tubes:
4 x 7591 output
3 x 12AU7
3 x 6AU6
2 x 6DS4
1 x 6SC6
1 x 6EA8
1 x 12AX7

Recommended Cables:

Kimber Kable - RCA Interconnects - Better

Kimber Kable - RCA Interconnects - Best

Kimber Kable - Phono Interconnects - Better

Kimber Kable - Flagship Phono Interconnects - Best

Testing Process:

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.

If the device has the ability to decouple the preamplifier from the power amplifier, we remove the jumpers and independently test each section. If the device cannot be decoupled, we assess the electronic condition of the piece by analyzing the speaker level output only.

We start by connecting the “preout” jacks of the receiver 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 section 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.

To test the tuner, we connect one of the tape outputs to the Sencore PA81 and the antenna terminals to a Sencore SG80 which allows us to “simulate” an ideal radio station using precision test signals instead of music. This device, in conjunction with an oscilloscope allows us to properly evaluate the following parameters:

1. AM Reception (Where Applicable)
2. FM Mono Reception & Tuning Meter Function
3. FM MPX Reception (Stereo)
4. Dial Tracking - How accurately the tuner dial or display indicates the actual frequency of the broadcast being received.
5. Stereo Separation - A properly working stereo tuner will have minimal crosstalk between the left and right channel.
6. Sensitivity & Signal Strength Meter Function - By lowering the output of the SG80 we can simulate weak stations and determine how well the tuner will be able to pull in weak distant stations. This adjustment also helps us verify signal strength meter function.

If the tuner has acceptable performance related to the parameters above, we connect the unit for listening tests with a simple dipole antenna. We listen for audio reproduction quality of local stations and evaluate how many stations the tuner can receive while we sweep through the dial. We are looking to verify that the tuner can decode stereo on strong local broadcasts and pick up a wide variety of local stations at the bottom, middle, and top of the frequency band. At this point we also test convenience features such as muting, filters, built in oscilloscope function, etc. 

Next, we test the power amplifier section by connecting the receiver’s speaker outputs to a Sencore PA81 Power Analyzer which acts as a dummy load, DC offset monitor, and oscilloscope interface. We start with a low level 1KHz test signal at the “main in” jacks and slowly increase its amplitude while monitoring the 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.

If the preamp and power amp both pass these tests, we reconnect the sections and verify that the preamp section can drive the power amp to rated power with a 1KHz tone on one of the line level inputs. 

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. This allows us to monitor the unit for signs of thermal runaway or intermittent issues that only crop up when the unit has fully come up to temperature