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A VEIN of reactionary conservatism resides deep inside nearly every audiophile. One of the greatest compliments that a member of the golden-ear club can pay a new amplifier, for example, is that it sounds "tube-like."

Is it any wonder that much of the surviving equipment from the peak years of the tube era costs considerably more now than it did when it was brand new? This is in spite of the fact that it can be a daunting task to keep tube gear performing at optimum levels.

The first problem, of course, is aging of the tubes themselves. The glowing filament inside a tube is much like the filament in a light bulb. It can eventually burn out. Even before it burns out, the tube's operating characteristics can slowly lose efficiency.

The cure is to check tubes at least yearly and replace those that have become marginal. Technically this is an easy task. Practically it is not so easy.

Back when tubes abounded, there were testers in many easily accessible locations. Every Radio Shack had one, for instance. Many drug stores did, too. Now walk-up testers have all but disappeared. The only place I've seen one recently is in Audio Center (3252 Sheridan Drive).

Finding replacements for defective tubes is only slightly easier than finding a tester. Audio Center has a large inventory of tubes and you can find good selections at electronics parts stores such as Summit Distributors (916 Main), Radio Equipment Corp. (196 Vulcan), or Genesee Industrial Electronics (2550 Delaware). Radio Shack outlets keep a few tubes on hand and will express order any others.

Be prepared to pay dearly for replacement tubes. The days of economical production of tubes by the thousands has long since past. Now tubes are a specialty product and are priced accordingly.

There's also some controversy concerning the quality of tubes currently being produced. At least one manufacturer has reportedly advised against replacing original tubes except in the case of total failure. The feeling is that old tubes in their declining years are still preferable to new ones of uncertain quality.

In the case of the classic Dynaco Stereo 70, it's now possible to replace the critical and costly driver tubes with a solid state module that accomplishes the same purpose. The module is fully assembled and comes with installation instructions. Contact Sutherland Engineering, P. O. Box 1363, Lawrence, Kansas 66044 for details of the Hybrid 70 module.

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