Dynaco ST 70 II Owners Manual

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STEREO 7O SERIES ll AMPLIFIER

CONGRATULATIONS on your choice of the Dynaco Series II " Stereo 70 tube amplifier. A
medium-power Class A push-pull design, the Series II 70 represents a thoroughly redesigned and
modernized version of the most popular stereo tube amplifier of all time.

INTRODUCTION. Tens of thousands of original Dynaco tube amplifiers are still in use around
the world. In fact, more quality music systems have included Dynaco tube preamps and power amplifiers
than any other combination. The original Dynaco Stereo 70 is a true classic still regarded with awe by
audio enthusiasts worldwide. The ST70 II marks the introduction of the second generation of vacuum
tube products bearing the Dynaco name. This new 70" fully reflects both the illustrious history of
Dynaco's involvement with vacuum tube designs as well as the latest advances in tube circuit technology.

Through its long history, the Stereo 70 has proven a robust, reliable design of exceptional value.
Dynaco has sought to preserve the considerable virtues of the original 70 while making fullest use of
much better and more modern parts plus advanced circuit techniques. When comparing old 70 with
new 70, one cannot help but notice the external similarity (i .e., the metalworkis of identical dimension
but with an entirely new connector array). Internally, however, the two units differ radically from each
other in both general appearance and execution of design. (Gone, for example, is nearly two-thirds of
all internal connecting wire.)

TUBE VS. TRANSISTOR. Tube amplifiers are THE choice among many knowledgeable
audiophilos, and they are preferred in severe service applications where even short-term failure must be
avoided. Tube designs are inherently able to withstand user and signal abuse that would instantly damage
solid-state electronics. Field replacement of socketed tubes is much more convenient than solid-state
parts. Generally speaking, tube amplifiers will give warning of impending breakdown. Sonically, tube
amplifiers do not clip as harshly as their solid state counterparts. Upon clipping. solid-state amplifiers
abruptly limit the signal resulting in the generation of high level distortion components (simulating a
square wave if driven hard enough). By contrast, tube circuits soft clip" (resulting in a more pleasant
compression rather than harsh clip). Ideally, neither is desireable. But a tube amplifier of modest power
specification can sound as full and rich as a very large, solid-state mplifier on dynamically rich music
passages. It is precisely these characteristics which are responsible for the tube sound so prized by
audio enthusiasts. Tube amplifiers are regarded by many as more musical even though their measured
specifications often appear far inferior to a comparably powered solid-state unit.

DESIGN PHILOSOPHY. Your ST70 Series II amplifier draws upon the proven design
philosophies of the original 70. The low open-loop gain philosophy is maintained, thereby minimizing
Transient Inter-modulation Distortion (TIM). TIM distortion is regarded in many circles as the type of
distortion to which the ear is most sensitive. The PentodefIriode gain circuitry is virtually the same as
original, thus keeping the signal path as short as practical without unnecessary distortion inducing
complexity. This is the true elegance of the Stereo 70. The output tubes remain the fine E134/6CA7 s.

The excellent output transformers are also unchanged from the original ST70. Three output
impedances are still available (i.e., 4, 8, and 16 ohm) - all properly matched with equal power ratings.