When open-reel tape became a quarter-track format with stereo in both directions of tape movement, the idea of "reversing" the tape for added playing time seemed strange.

On critic, David Hall, wrote about "The Gentle Art of Tape Flip-Flop." He rhapsodized on the wonderment of a full major musical work contained on one seven-inch reel while gently chiding the industry for compelling us to develop the new manual skill of lifting the two tape reels (supply and take-up) from their spindles on the deck, turning both over, and replacing them in their respectively opposite positions, all the time being careful not to twist or snarl the tape. Even then, pressing the play button to hear the second half of the recorded program seemed a violation of some basic tape-deck principle, since with older tapes, made before the quarter-track technique, doing that would result in literally backward sound.

But the reverse-play idea did work, and soon everyone who owned a tape deck was indeed mastering the "gentle art of tape flip-flop," which enabled you to play the opposite-recorded material without turning over the tape reels. A few decks even offered reverse-record. Automatic reverse was accomplished either by adding a subsonic signal or, more often, by attaching a small snip of sensing foil to the tape.

In the cassette format, reverse play and record have been less than prominent with one notable exception. Dual (the West German manufacturer whose products are sold in the U.S. by United Audio) always espoused this feature and has developed it to a fine point in its latest cassette deck, the model C-839RC.

This machine plays and records in both directions automatically and can even be programmed to repeat an entire cassette. This feature works with any cassette; there is no need to add a subsonic reversing signal to the tape, or to attach a sensing foil. The deck's own electronics take over and do the job. This means, for instance, that one can hear the entire Beethoven "Eroica" (DGG923 063) or a full "volume" of Chopin Nocturnes (In Sync C 4025) without undue distractions or breaks, as they were meant to be heard. And when making up your own stereo programs using the Dual reverse-record feature, you can adapt the music you are taping more suitably to each side of the tape while also making the most of the given tape length.

Despite its "lower" model number, the Dual C-839RC is a more advanced deck than an earlier Dual C-939. The present model is a front-loader for easier installation. It uses two motors instead of one. Tape handling capability includes the recent metal formulations. Transport controls are "feather-touch" with fast-button options, and signal-metering is more sophisticated. The deck still uses a combined record/play head, which means no monitoring off the tape during recording. But note that the tracks on the head are switched electronically for reverse mode, which is far better than physically moving the head.

As expected, the new Dual with its improved features and performance costs more than the older version -- $850 as compared with $580. Be that as it may, automatic reverse that works as well as it does in the C-839RC seems more important and relevant from a musical standpoint than do most of the microprocessing and timing gimmicks found in many other similarly or higher-priced cassette decks. FEED -- BACK

Q. A couple of amplifiers I've seen recently are advertised with "volts out" rather than power in watts. How come? How do you know what their power output is?

A. The "how come" question is hard to answer. It may be an attempt to appear more "technically astute" or somehow "different" from the competition. There is some justification insofar as solid-state amplifiers are constant-voltage devices -- that is, they deliver the same voltage regardless of load. What does change with the load (and with frequency) is the current and thus the usable power. As an approximate guide, the power is equal to the square of the voltage divided by the load impedance. Thus, for instance, a "15-volt output" amplifier presumably will supply about 56 watts into a 4-ohm load; 28 watts into an 8-ohm load; 14 watts into a 16-ohm load.