In 1960/61, McIntosh Laboratory, at the dawn of stereo, introduced their MC275 stereo power amp.
It may look quaint and primitive by today's standards, but it introduced many innovations including the way the transformers were wound (an audio black art and something that McIntosh has owned its entire life) and circuit tweaks to widen the bandwidth and lower the distortion beyond expectations in tube amps. It also put out 75 watts per channel (hence the model name), which was considered a whopping amount in 1961 with its big high-efficiency horn-loaded speakers. It weighed 65 lbs. A typical tube amp or receiver in 1960 might put out 10-15 wpc.
Ten years after its introduction, McIntosh caved to the solid state onslaught and reluctantly retired the MC275. But over the years there was a vocal contingent that refused to let this design die. It became one of the most sought after pieces of kit on the vintage audio market. Finally in 1993 McIntosh released a commemorative reissue to honor the passing of former Mac president Gordon Gow, who originally had been McIntosh's chief engineer behind their game-changing products, including this one. The commemorative edition sold beyond McIntosh's expectations, so they gradually re-introduced this amp into their product line, incrementally upgrading it just as any good product would be improved over time for better performance and reliability. A more detailed description of the evolution of this amp between the 1993 Commemorative and the Mark IV can be read here.
Stereophile reviews the current iteration, Mk V, in the October (2010) issue. The results range from revealing to astonishing. Concerning the changes that bring it to Mk V, as far as I could discern, very little has changed in the circuit design; the changes are in the implementation and the parts list. For example, the chassis is now made out of polished stainless steel instead of chrome plated sheet metal, which after bending into shape was prone to crack and flake off plating over time. The 3 circuit boards of the 1993 commemorative version (1961 original was PTP) have been consolidated to one. The transformers are still wound according to McIntosh's proprietary formula on the original machine from 50 years ago, but now use high-tech plastic insulation rather than ceramic coating on the transformer wire of the original. The old coating tended to get brittle and flake off over time. Resistors are now chosen with a 1% tolerance of variation. Power tube sockets include chimneys to operate the power tubes at optimum temp and help them last longer. And the input/output terminals have been brought into the 21st century--5-way binding posts for the speakers replace the dinky terminal strips of all previous versions and there are now balanced inputs available. It's sort of like having your engine blue-printed. It's technically all stock, but built to closer tolerances and therefore runs better and lasts longer.
So how did this thing come out in the test report a full 50 years after the original was released? Usually when I read test reports on tube amps, they get great marks for transparency, nuance, and a very organic midrange, but get markdowns for treble extension and bass tautness. Not this one. Into 8 ohms, the response curve was pretty much flat to 20KHz and the -3dB point was way out at 91 KHz. That's wide bandwidth in pretty much anybody's book, only occurs in a few of the more esoteric tube amp designs today, and is pretty much unheard of in a 50-year-old design. Closely tied with this wide bandwidth was near textbook-perfect square wave response. The tops were dead flat, indicating good extended bass response and no ringing, the rise lines were close to vertical, and the corners were sharp and square like a wide bandwidth solid state amplifier. When the treble response drops off, it always means a slower rise time with rounded corners on the square waves like the one on the left. The MC275 looked more like the one on the right, but it was even flatter on the top and overall more square. The square wave on the right is from a test on a pair of 2009 state-of-the-art monoblock solid state amps priced at $16,500/pair.
This square wave on the left is from the test report on a same-era (~ 1958) highly regarded integrated tube amp of the time, the Eico HF-81. The McIntosh wave (pic not available) matches that of most good, fast solid state amp and is better than most very expensive tube high end amps made today, which either have rounded (limited treble response) or notched (abrupt high treble spikes in the frequency response) corners.
And how about those "noisy tubes"? Its signal-to-noise ratio tested out at over 100 dB. The net result is that Stereophile placed this 50-year-old design amp in their Class A recommended components for October, 2010; most of the other amps in this category cost in the high four figures and some reach into five. This McIntosh? MSRP of $4500. Although $4500 may seem like a lot for a 75 wpc stereo amp (it actually tested out at over 90 wpc), consider these things: A good guitar amp head can easily reach over $2K and even the best boutique head is not built to the exacting tolerances of this amp. Second, this amp is only about twice as much as many "budget high end" solid state power amps designed in the USA or UK and then built in the Far East (Adcom, Parasound, Rotel, Cambridge, Musical Fidelity, AudioSource, etc.). These are semi-handbuilt in the USA in the original Binghamton NY facility. And let's not forget what those tubes and transformers add to the cost. The amp can also be switched to work as a 150 wpc mono amp. A pair of mono 150 watt tube amps at $9000 is very competitive in this market.
Here's a pic of the newest version. You can see on the left side that the I/O panel has been updated with the gold-plated 5-way binding posts for speakers. The reason there are so many of them is because those huge output transformers offer separate positive terminals for 4-, 8-, and 16-ohm speakers. To the right are the balanced XLR and single-ended RCA inputs.
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JohnnyB
In 1960/61, McIntosh Laboratory, at the dawn of stereo, introduced their MC275 stereo power amp.
It may look quaint and primitive by today's standards, but it introduced many innovations including the way the transformers were wound (an audio black art and something that McIntosh has owned its entire life) and circuit tweaks to widen the bandwidth and lower the distortion beyond expectations in tube amps. It also put out 75 watts per channel (hence the model name), which was considered a whopping amount in 1961 with its big high-efficiency horn-loaded speakers. It weighed 65 lbs. A typical tube amp or receiver in 1960 might put out 10-15 wpc.
Ten years after its introduction, McIntosh caved to the solid state onslaught and reluctantly retired the MC275. But over the years there was a vocal contingent that refused to let this design die. It became one of the most sought after pieces of kit on the vintage audio market. Finally in 1993 McIntosh released a commemorative reissue to honor the passing of former Mac president Gordon Gow, who originally had been McIntosh's chief engineer behind their game-changing products, including this one. The commemorative edition sold beyond McIntosh's expectations, so they gradually re-introduced this amp into their product line, incrementally upgrading it just as any good product would be improved over time for better performance and reliability. A more detailed description of the evolution of this amp between the 1993 Commemorative and the Mark IV can be read here.
Stereophile reviews the current iteration, Mk V, in the October (2010) issue. The results range from revealing to astonishing. Concerning the changes that bring it to Mk V, as far as I could discern, very little has changed in the circuit design; the changes are in the implementation and the parts list. For example, the chassis is now made out of polished stainless steel instead of chrome plated sheet metal, which after bending into shape was prone to crack and flake off plating over time. The 3 circuit boards of the 1993 commemorative version (1961 original was PTP) have been consolidated to one. The transformers are still wound according to McIntosh's proprietary formula on the original machine from 50 years ago, but now use high-tech plastic insulation rather than ceramic coating on the transformer wire of the original. The old coating tended to get brittle and flake off over time. Resistors are now chosen with a 1% tolerance of variation. Power tube sockets include chimneys to operate the power tubes at optimum temp and help them last longer. And the input/output terminals have been brought into the 21st century--5-way binding posts for the speakers replace the dinky terminal strips of all previous versions and there are now balanced inputs available. It's sort of like having your engine blue-printed. It's technically all stock, but built to closer tolerances and therefore runs better and lasts longer.
So how did this thing come out in the test report a full 50 years after the original was released? Usually when I read test reports on tube amps, they get great marks for transparency, nuance, and a very organic midrange, but get markdowns for treble extension and bass tautness. Not this one. Into 8 ohms, the response curve was pretty much flat to 20KHz and the -3dB point was way out at 91 KHz. That's wide bandwidth in pretty much anybody's book, only occurs in a few of the more esoteric tube amp designs today, and is pretty much unheard of in a 50-year-old design. Closely tied with this wide bandwidth was near textbook-perfect square wave response. The tops were dead flat, indicating good extended bass response and no ringing, the rise lines were close to vertical, and the corners were sharp and square like a wide bandwidth solid state amplifier. When the treble response drops off, it always means a slower rise time with rounded corners on the square waves like the one on the left. The MC275 looked more like the one on the right, but it was even flatter on the top and overall more square. The square wave on the right is from a test on a pair of 2009 state-of-the-art monoblock solid state amps priced at $16,500/pair.
This square wave on the left is from the test report on a same-era (~ 1958) highly regarded integrated tube amp of the time, the Eico HF-81. The McIntosh wave (pic not available) matches that of most good, fast solid state amp and is better than most very expensive tube high end amps made today, which either have rounded (limited treble response) or notched (abrupt high treble spikes in the frequency response) corners.
And how about those "noisy tubes"? Its signal-to-noise ratio tested out at over 100 dB. The net result is that Stereophile placed this 50-year-old design amp in their Class A recommended components for October, 2010; most of the other amps in this category cost in the high four figures and some reach into five. This McIntosh? MSRP of $4500. Although $4500 may seem like a lot for a 75 wpc stereo amp (it actually tested out at over 90 wpc), consider these things: A good guitar amp head can easily reach over $2K and even the best boutique head is not built to the exacting tolerances of this amp. Second, this amp is only about twice as much as many "budget high end" solid state power amps designed in the USA or UK and then built in the Far East (Adcom, Parasound, Rotel, Cambridge, Musical Fidelity, AudioSource, etc.). These are semi-handbuilt in the USA in the original Binghamton NY facility. And let's not forget what those tubes and transformers add to the cost. The amp can also be switched to work as a 150 wpc mono amp. A pair of mono 150 watt tube amps at $9000 is very competitive in this market.
Here's a pic of the newest version. You can see on the left side that the I/O panel has been updated with the gold-plated 5-way binding posts for speakers. The reason there are so many of them is because those huge output transformers offer separate positive terminals for 4-, 8-, and 16-ohm speakers. To the right are the balanced XLR and single-ended RCA inputs.
And I want one. Bad.
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