Founded by David Hafler and Ed Laurent in Philadelphia, Pennsylvania in 1955, Dynaco was an American hi-fi audio system manufacturer popular in the 1960s and 1970s for its wide range of affordable, yet high quality audio components.. Its best known product was the ST-70 tube stereo amplifier. They also manufactured other tube and solid state amplifiers, preamplifiers, radio tuners and bookshelf loudspeakers. Dynaco was liquidated in 1980, and the trademark is now owned by Radial Engineering Ltd.
Early company history
In 1950 David Hafler and Herb Keroes started a Philadelphia-based company called Acrosound to build and sell audio-quality output transformers, primarily for home electronics hobbyists. The two men refined and developed the ultra-linear audio circuit pioneered by British audio electronics engineer Alan Blumlein, using taps from the output transformer to feed signal back into the output stage screen grid circuitry. The Acrosound transformer circuit was later used in many home-built and commercial hi-fi amplifiers in the early 1950s. In order to appeal to a wider consumer market, Hafler decided to design and build entire power amplifiers as build-it-yourself kits, complete with preassembled, tested circuit boards that only required the customer to wire the boards to the transformers, controls, and power supply to complete the project. This was a considerable advance over other audio system kits of the day, which generally required the purchaser to assemble and test the PC boards themselves, a relatively precise and time-consuming task.
In 1954 Dave Hafler and Herb Keroes parted company. During a visit to the New York-based Brociner Electronics the same year, Hafler met an audio engineer named Ed Laurent, who had designed a novel single-tube driver circuit for a power amplifier. In 1955, the two men founded the Dyna Company (later Dynaco) with the intention of not only producing transformers but high-quality audio circuitry. The company was incorporated in October 1955, with business premises located at 617 N. 41st St in Philadelphia. Dynaco's first product was the Mk. II 50-watt power amplifier. Available as a kit or preassembled unit, the Mk. II was sold for several years until its replacement in 1956 by the Mk. III amplifier, which produced 60 watts. Hafler wrote an article for Radio-Electronics Magazine in 1955 delineating the design of a high-power version of the Williamson amplifier using ultra-linear circuitry and Dynaco's new output transformers. The Williamson amplifier utilized a slightly different circuit design from the Mk. II and Mk. III. Shortly thereafter, the company moved its business operations to 3912 Powelton Avenue in Philadelphia, where they remained for several years.
Products
Today, Dynaco is best remembered for its highly regarded vacuum tube stereo amplifier, the Stereo 70 (ST 70). Introduced in 1959, the ST 70 was available as a kit (Dynakit) intended for assembly by the purchaser or as a complete factory-wired unit. The ST 70 used four EL34 output tubes, one GZ34/5AR4 rectifier tube, two 7199 input (driver) tubes, two output transformers, one power transformer, and a preassembled printed circuit board (PCB) containing the driver circuit. It produced 35 watts per channel. The driver circuit had a single 7199 pentode/triode tube per channel and used the driver tube to handle both voltage amplification and phase splitting. The output transformers are an ultralinear design, whereby part of the primary winding is fed back to the output tube's screen grid. This design reduced distortion and improved audio quality.
A masterpiece of efficient circuit design, the ST 70 provided reliable, high-quality audio amplification at an affordable price. The popularity of the ST 70 contributed more than any other single product to continuing consumer interest in tube-based stereo amplifiers at a time of increasing market dominance by solid state audio products. Because of its excellent value for cost, Dynaco tube amplifiers were often referred to as "the poor man's McIntosh." More than 350,000 ST-70 amplifiers had been sold when production finally ceased, making the ST 70 the most popular tube power amplifier ever made.