Integrated Amp Reviews

The most important thing you can do with a thermionic valve is to hold it in your hand and study it with your eyes. More than you might think, what you see is what you get. High-energy electrons are boiled off the heater or cathode, pass through the wire control grid, and collide forcefully with that big black, gray, or silver thing—the anode, or "plate"—that occupies most of the space inside the bottle. What that anode structure looks like is probably what your midrange will sound like—ie, if the anode looks smooth and big and richly textured, those same qualities are likely to apply to the sound of the midrange. Study the texture, shape, and color of any tube's anode, then use it play to some Frank Sinatra or Ella Fitzgerald: You might be surprised to discover the usefulness of this maxim!

For more than a year, I used the Line Magnetic LM-518IA with its stock, Chinese-made Shuguang tubes: They sounded first rate, never misbehaving or making me wish for better. Everything I've written in this review is based on my experience with the standard Shuguang tubes.

Then I told Jonathan Halpern of Tone Imports, which distributes LM products in the US, that I was writing this review. He urged me to at least try the LM-518IA with some new old stock (NOS) tubes. "You will be surprised," he swore. I asked him and several of my friends to loan me some 12AX7s and 6L6s; I already had a few cool 5AR4/GZ34 rectifiers. I was hoping to cop some RCA, G.E., Elrog, or Psvane 845s, but no luck so far—yet I did score some vintage smooth-plate Telefunken 12AX7s, and some vintage East German Siemens box-plate ECC8035/ECC83s.

The LM-518IA uses as input-voltage amplifiers a pair of 12AX7s, and changing from the stock Chinese versions of those tubes (which have a somewhat dull and flavorless character) to these vintage exotics made a significant, enjoyable, but not earth-shaking difference. The box-plate Siemens tubes jacked up the richness and color quotients, while the legendary smooth-plates made it sound as if someone had sent a team of maids to clean my apartment, fold my clothes, and set a vase full of fragrant flowers on every horizontal surface.

Switching from a Chinese 5AR4 rectifier tube to a Dutch Amperex Bugle Boy 5AR4/GZ34 made a change that was a bit subtler but perhaps even more rewarding. The Bugle Boy removed a previously unnoticed "electricalness" from the overall sound and replaced it with an unmistakable organic naturalness. (Note: Tube amps can be divided into two distinct types: those with tube rectification and those with solid-state diodes. The sounds of amps with tube rectifiers tend to be more natural and less mechanical, and to flow better, than those with solid-state rectifiers.)

Then I went crazy. I replaced the 6P3P driver tubes, first with a pair of metal-envelope G.E. 6L6s (a nice, slightly richer-sounding upgrade at very low cost) and, finally, with some expensive NOS Western Electric 350B beam power tubes. The WEs gave me the impression that the LM-518IA was capable of reaching even deeper into the music, yet there was also a reduction in that "May–June" bright-emitter lighting that I found so engaging. The WEs further enhanced musical textures and made the LM-518IA sound like a more luxurious and expensive audio product—but I still preferred the simpler, more lively neutrality of the G.E. and Shuguang tubes. My experiments in tube rolling were rewarding and fun. They also proved that Shuguang makes good tubes.—Herb Reichert