The Dynakit Stereo 70 (commonly known as the Dynaco ST-70) is one of the most famous and enduring tube audio amplifiers ever created. Introduced in 1959 by David Hafler’s Dynaco company, it sold over 350,000 units, making it the most popular tube amplifier in history. It was sold both as a factory-assembled unit and as a “Dynakit” DIY build project.
Core Specifications
The original ST-70 circuit is celebrated for its warm, classic “vintage” sound signature and highly reliable push-pull design: [1, 2]
Attribute
Specification
Power Output
35 Watts per channel (Class A up to ~15W, then Class AB)
Output Tubes
(4) EL34 / 6CA7 (matched pairs)
Driver Tubes
(2) 7199 pentode/triode tubes (or 6GH8A/6U8A with modifications/adapters)
Rectifier Tube
(1) GZ34 / 5AR4
Frequency Response
20 Hz to 20 kHz (+/- 1 dB)
Output Impedances
4, 8, and 16 Ohms (via rear barrier terminal strips)
