The Dynaco / Dynakit ST-70 Tube Amplifier

Dynaco is best known for its superior vacuum tube based stereo amplifier, the Stereo 70 (ST-70). It was released in 1959. Two versions of the amplifier could be purchased - the Dynakit, which was designed to be self-assembled by the customer, and the fully constructed Dynaco 70 "factory wired" model.

The ST-70 requires four EL34 output tubes, a GZ34/5AR4 rectifier tube, two 6GH8A input tubes. It has two output transformers, one power transformer, and the driver circuit is printed on a circuit board (PCB). This driver circuit consists of a single 6GH8A pentode/triode per channel, executing both voltage amplification and phase splitting.

The output transformers have an ultra linear architecture, wherein a portion of the primary winding is relayed to the output tube screen grid. This configuration reduces distortion and enhances sonic fidelity. The amplifier produces 35 watts per channel.

Boasting the utmost sound quality for a moderate cost, the Dynakit Stereo 70 is a complete two-channel (35-watt per channel) power amplifier arranged in a space-saving and attractive design.

It uses a patented circuit with outstanding performance characteristics, along with top quality parts, including the new Dynaco Super-Fidelity A-470 transformers - the finest available. The combination of high-grade components and innovative design ensures excellent sound and reliability, offering top level performance across a wide range.

The measured specifications show that the Stereo 70 is an amplifier of unequalled performance, and its listening quality is also unrivalled by any regardless of price.

Providing the power necessary to drive loudspeakers at any sensitivity, this amplifier offers two separate 35 watt channels for stereophonic listening. The channels can be paralleled for a full 70 watts of low distortion monophonic output.

The elevated power output and low internal resistance deliver superior damping properties and compatibility with a wide range of premium speaker systems, needing no alterations for specific speaker setups.

The design features of your Dynakit which contribute to its superior listening quality include some elements which are not revealed by the customary steady-state laboratory measurements.

For example, it does not exhibit bounce and flutter when pulsed with a transient signal. Thus a sharp percussive signal like a drum beat or a piano note will be reproduced with sharpness and clarity and result in neither overhang nor muddiness.

The Stereo 70, unlike many other amplifier circuits, has been designed to provide its specified performance on a loudspeaker load, not just under laboratory measuring conditions. Therefore, the connection of a loudspeaker to the amplifier does not deteriorate its performance or listening quality.

The output transformers employed in the Dynakit ensure that its power handling capability remains consistent across the audio range, eliminating the typical increase in distortion experienced by many amplifiers at both the highest and lowest frequencies.