"Who would think that this old design with its old parts could perform with refinement and grace."

I have had this integrated amplifier languishing for more than three years. "It's in need of slight repair" the former owner, Gilbert de Frenne of Orinda, California, forewarned me when I first expressed interest in purchasing the LK-72. It needs replacement of coupling caps. "Don't even think of switching the amp on until then" he reiterated, "or you'll fry the 7591 tubes." The 7591 tubes are not easy to find and they are expensive as well so I heeded his advice. A few days after receiving the amp, I took a cursory look at its innards. There was no telltale evidence that it needed repair. The capacitors and resistors looked pristine. But perceptions can be deceiving, right? My overall impression was this unit had been professionally assembled and well cared for afterwards. Having very little time to pursue the inspection further, I dismissed the LK-72 to its solitary corner.  I also purchased from Gilbert an extra pair of used 7591 tubes and a Scott LT-110 FM stereo tuner to complement the LK-72. The tuner and amp make a  perfect cosmetic set. I've had no problem with the tuner, and have been using it with my third sytem located in the reading room.

Technical description

The LK-72 was designed in 1960, based upon the circuit diagram that came with the instruction book. During its time, it must have been a marvel to have a high grade stereo amplification system within one compact package. Man's drive to make things smaller is not a new trend. In this instance, it's been around for 38 years or more.

As an integrated unit, the LK-72 is composed of a control preamplifier and a power amplifier. One can easily recognize the tube components used for each purpose. Near the front are the preamp tubes, four 12AX7 tubes: two for the phono and another pair for the line. Right behind the 12AX7s are the tubes for the amplifier, two 6GH8s and four 7591 output tubes. The integrated amp also employs a 5AR4/GZ34 rectifier tube. At the back are the two large and heavy output transformers. The arrangement is well-organized and elegant in its horizontal symmetry.

Typical of preamps produced at that time, the LK-72 offers separate treble and bass controls, derived center channel output level, stereo selector and input selector. These controls use brown cylindrical knobs with gold edging to match the gold faceplate. A slide switch is provided for equalization (RIAA or NAB Tape), scratch filter, and volume loudness. The chassis is made of aluminum for better head dissipation.

The amplifier section is rated at 35 wpc. H.H. Scott amplifiers operate all tubes particularly output tubes well below the manufacturer's design center. In this particular instance, the output tubes of the LK-72 operate at 75% of manufacturer's average. This assures long tube life and eliminates the need for tube matching and biasing. For low distortion, the DC Balance for each channel must be adjusted periodically. The procedure is easy to follow, and requires a voltage meter and 16 ohm resistors.

First Impression

The following components were used to evaluate the LK-72 integrated amp: Audible Illusions Modulus 3, Counterpoint SA-5.1 and Audio Research SP6B preamps, Classe DR-9 amp, Audio Research D-115 MkII amp, Pink Triangle Turntable with Sumiko MMT and Promethean Green cartridge, JVC XL-Z1050 compact disk player all connected through an Inouye power conditioner, Yamaha NS1000M monitor speakers with Target stands, Kimber 8TC speaker cables and MIT interconnects.

Cosmetically, the LK-72 radiates classic elegance. The gold faceplate, aluminum chassis, methodical arrangement of tubes, large output transformers, tubular resistors (this is the first time I have seen these), and aluminum capacitors intertwine to create the perception that this is one well thought out and very accomplished product. And it is. I had a positive first impression about this amp.

As indicated earlier, the amp needed a bit of repair. We were fortunate in Dallas to have access to surplus electronic parts. As much as possible I wanted the amp to perform in accordance with its original design, parts, and listening experience. I wanted to preserve the designer's intent. So I eschewed polypropelene caps and opted for mylars. Why? Because in my experience, polypropelenes change the presentation, and not always for the better. I replaced the four original .22 mfd white caps with 2.0 mfd 400v Century mylar caps, checked all of the tubes with my tube tester, installed these and fired up the LK-72. Following the instructions from the manual I adjusted the DC balance, and left the unit on for several hours for observation. Then I hooked it up and listened. It sounded swell though a bit thin at the top at first. As it warmed up the thinness gradually diminished. Off and on I used it over a period of over two weeks.

I would have stopped here and started more serious listening but I wanted to minimize the possibility of frying  the 7591 output tubes. The selenium rectifier has been known to be the weak link in the bias supply and prone to malfunction. I replaced this with a 3 amp 1000 PIV bridge rectifier, an overkill but the part was inexpensive. To round out my work, I replaced the 15K ohm 25w tubular resistor that can be seen behind the power transformer with a new old stock. The original looked worn though it was within spec. I just wanted the LK-72 to look good. Since then I have used the integrated amp for over three months.

Little did I know

Integrated amps have often been historically overlooked and disparaged by the audio purist. Lately there seems to be an increasing acceptance that this form factor is worthy of more serious work. Now we see high-end manufacturers like Audio Research, Conrad-Johnson, VTL and Classe adding integrated amps to their product line. This turnaround is refreshing.

From the start, the LK-72 established its musical credentials. As stated earlier, initially there was a thinness in the highs which was somewhat irritating. Through time however this dissipated. The new caps probably needed breaking in. Listening through the phono was a surprising experience. Who would think that this old design with its old parts could perform with refinement and grace. To find out an amp's dynamic capability, I sometimes listen to Phil Collins Face Value album (Atlantic SD 16029). The first cut, "In the Air Tonight," is particularly suited for this purpose. Considering its meager power rating, the LK-72 did not disappoint. It delivered about 75% of the visceral impact that the DR-9 so effortlessly provides. Nevertheless, one could follow the bass line as it cohesively melded with the other instrumentation and vocals. I followed this up with the Eagles Desperado (Asylum SD 5068). I had not listened to this album in a while. The first cut, "Doolin Dalton," is a musical feast. I was taken by the LK-72's ability to render this competently. All of the audiophile criteria were present as well: "sweet, musical, clear, bloom."

Weaknesses

While the LK-72 is a competent performer, it nevertheless has a number of weaknesses. Foremost is its opaqueness--its relatively low resolution. It lacks the crispness of the VTL 120/50 or the incandescence of the ARC D-115 MkII. Through the LK-72, the leading or fading crystal clear harmonics are less discernible and softer. It is not noticeable or distracting. This tends to lull the listener into musical satisfaction. And that's a great thing about this amp. But if you are the type who places harmonic extraction very high on your priorities, then look elsewhere. The second notable weakness of the LK-72 is its dynamic contrast. I suspect this is due to its power rating,  power supply design, and tube complement. Unlike the 6550's or the KT88's, the 7591's seem to have a more relaxed presentation. The effect is narrower dynamic scale and less space to the music. As expected, it also falls short in bass definition. No surprise here, given the weaknesses described earlier. 

Summing up

 The Scott LK-72 tube integrated amp should be a tired, old and outmoded piece of electronic component. With advances in technology this anachronism has no right to sound this credible. Yet it does. 

Yes it is not high up there in the hallowed list of high-end products. Hey, those things cost thousands of dollars. The LK-72 remains a fine piece of electronic art especially in today's standards. It is worthy of owning and keeping. I'd listen to it any day. Recommended indeed. 

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