Dynaco power amplifiers

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The Dynaco ST-70 Series 3 Tube Amplifier is Now (Finally!) Shipping

Previewed in 2016, and originally scheduled for Spring 2017, Dynaco (a division of Radial Engineering Ltd.) announced the ST-70 Series 3 tube amplifier is now shipping. Since acquiring the legendary Hafler and Dynaco brands in 2014, Radial Engineering has been carefully working on the Dynaco ST-70 Series 3 tube amplifier, in an effort to create a truly worthy successor of one of the most successful tube amplifiers of all time. The result is finally available! 
 

The Dynaco ST-70 builds upon the proven design philosophies of the original David Hafler-designed Stereo 70, with contemporary design techniques resulting in exceptional performance improvements that meet the requirements of modern music enthusiasts. The ST-70 provides 35 watts per channel and is switchable between both 4 and 8 Ohm outputs, with Class-A push-pull stereo topography that has long been characterized as a reliable design with exceptional audio quality.

audioXpress May 2017 included a detailed articleon this historical revival project.  As stated by Dan Fraser, the Senior Design Engineer responsible for the Radial Engineering team who designed the new generation Dynaco ST-70 Series 3, all the options needed to meet the expectations that come with David Hafler’s work were considered. “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. This “new ST-70 Series 3” reflects the illustrious history of Dynaco’s involvement with vacuum tube designs as well as the latest advances in vacuum tube technology. We like to think of the ST-70 Series 3 as the update that David Hafler would have made if he were alive today.”
 

This latest rendition has seen a substantially overhauled power supply from the original version, employing a larger dual-primary power transformer with improved line regulation, increased filter capacitance, and a solid-state rectifier that results in a much more articulate response. The redesigned front end of the Series 3 amplifier replaces the obsolete 7199 pentode signal tubes from the original Stereo 70 with more commonly-used 12AU7 dual-triode tubes, while the output stage and EL34/6CA7 output tubes retain the same elements as the original Stereo 70. A set of front-panel recessed trimmers has been provided, allowing the bias adjustment to be fine-tuned for each output tube.

Building on the legacy of David Hafler's enormously successful Stereo 70, the new Dynaco ST-70 - MSRP: $2,999.99 USD - incorporates advancements in component quality, improvements to the electronic circuit performance, and an all new exterior design that is sure to please the most demanding music enthusiasts.  

More information on the new Dynaco ST-70 is available here: www.dynaco.com/st70
www.dynaco.com| www.hafler.com| www.jensen-transformers.com
www.radialeng.com
Sours: https://audioxpress.com/news/the-dynaco-st-70-series-3-tube-amplifier-is-now-finally-shipping

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Dynaco

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..[1] 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[edit]

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.[1] 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.[1] The Acrosound transformer circuit was later used in many home-built and commercial hi-fi amplifiers in the early 1950s.[1] 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.[1] 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.[1]

In 1954 Dave Hafler and Herb Keroes parted company.[1] 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.[1] In 1955, the two men founded the Dyna Company (later Dynaco) with the intention of not only producing transformers, but high-quality audio circuitry.[1] The company was incorporated in October 1955, with business premises located at 617 N. 41st St in Philadelphia.[1] Dynaco's first product was the Mk. II 50-watt power amplifier.[1] 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.[1] 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.[1] The Williamson amplifier utilized a slightly different circuit design from the Mk. II and Mk. III.[1] Shortly thereafter, the company moved its business operations to 3912 Powelton Avenue in Philadelphia, where they remained for several years.[1]

Products[edit]

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.[citation needed]

A smaller tube amplifier, the 17.5wpc Stereo 35, was introduced in 1963, and was followed the next year by the SCA 35, the company's first integrated (preamp + power amp) tube amplifier. In 1992, an updated version of the Stereo 70, the Stereo 70 II, was produced by Sound Valves for Panor Corporation. Even today, upgraded components, rebuilding kits, and complete tube amplifiers using the basic Stereo 70 design are still in production, and the ST 70 has inspired numerous other amplifier designs, such as Ars-Sonum's Filarmonia SE. Dynaco continued to build both mono and stereo amplifiers until 1977.

The company's final contribution to vacuum tube technology was the massive Mk. VI mono power amplifier of 1976, which produced 120 watts (continuous).

In later years, the company began to produce a line of solid-state audio components, commencing in 1966 with the introduction of the Stereo 120 power amplifier (60 wpc). Because of early problems involving circuit, power supply, and transistor failures, the ST 120 was not as popular as earlier Dynaco tube amplifiers. Numerous small circuit changes were introduced by Dynaco over the years in an attempt to improve the stability and reliability of the ST 120, without much success. With the PAT-4 preamplifier in 1967, the company affirmed its ability to design reliable solid state equipment at an affordable price. In 1969 the Dynaquad 4-channel matrix decoder system was introduced, helping to start the quadrophonic sound craze. In the 1970s, the Stereo 400 was developed and marketed. This was a high power amplifier at 200 watts per channel that offered automatic protection circuitry to prevent electrical destruction of the loudspeaker. The FM-5 tuner was offered as was the SCA-80 integrated amplifier in the early 1970s time line. Dynaco's solid-state kits were different from the popular Heathkit products (and Dynaco's own vacuum tube kits) because of their preassembled circuit boards. These boards were wired at the factory, tested and packaged with the unassembled chassis. It remained only for the consumer to attach the switches and controls to the chassis pieces, assemble the chassis and power supply, and solder connecting wires to the circuit boards. This saved considerable time and reduced error in assembly.

Dynaco also distributed the famous SEAS 'A-Series' of bookshelf loudspeakers that were manufactured in Denmark, using input from Dynaco's David Hafler and SEAS's Ragnar Lian. The A-Series were marketed between from 1970 until Dynaco's demise in the 1980s. The Dynaco A-25 model proved to be extremely successful, selling between 600,000 and 1,000,000 units.[2] A modified aperiodicbass reflex design using SEAS speakers in a handsome wood cabinet, the A-25 sold for $79.95 each in 1969[3] making it competitive with much more expensive loudspeakers. The patented aperiodic (essentially non-resonant) woofer design utilized a highly damped vent instead of a reflex port, whose acoustic resistance is very carefully controlled. The resistant venting action lowered the "Q" of the system and reduced impedance variation near resonance in the A-Series speakers. Dynaco followed the A-25 with the slightly larger A-35, which featured a dual-chambered, non-vented design in a walnut-veneered cabinet with even greater transparency and fidelity. Over time, Dynaco marketed a wide range of loudspeakers, ranging from the small A-10 model to the floor standing A-50 series. After some 30 years, these loudspeakers still command good prices in markets such as eBay, and are a testimonial to their quality.

Concurrent with A-25 production, Dynaco introduced the QD-1 speaker adapter which synthesized 4-channel sound from the stereo amplifier output. This "Dynaco patent" required a single resistor and a threeway potentiometer for the two rear speakers, generating phase difference signals for a feeling of ambience. The system worked best when the stereo sound had been recorded via two bidirectional microphones on the same spot. When microphone set-up changed to the use of multiple directional microphones and multitrack tape recording and postprocessing (i.c. in the CD era), the QD-1 was less effective.

Dynaco became a wholly owned subsidiary of Tyco, Inc. in 1969. David Hafler remained with the company a few years longer, but left in 1974 to join Ortofon, manufacturer and importer of high-end phono cartridges. In 1977, Hafler founded the Hafler Company, continuing the tradition of high quality but inexpensive kits and assembled hi-fi gear.

In the late 1970s, Dynaco released a short-lived set of new loudspeakers developed by Ed Laurent, the Phase III. The speakers were well regarded by the audiophile community, but their introduction was apparently too late to make any strong impression in the marketplace, and Ed Laurent left shortly afterward to join SEAS Corporation. After Dynaco closed its USA operations, its former Canadian subsidiary released the Dynaco A-150, A-250, and A-350 speakers, all manufactured in Canton, Massachusetts.[1] Critical reviews of the new audio speakers were not favorable, and they disappeared from the market in the mid-1980s.[1]

Sale of company[edit]

Dynaco was acquired by ESS Labs, LLC in 1979; the Dynaco division was closed in 1980 and its assets acquired by Stereo Cost Cutters (later called Sound Valuesand Sound Valves).

In 1991 the Pan Orient Corporation (later Panor Corporation) acquired the Dynaco trademark, and in 1993 began marketing electronic audio components with the Dynaco brand. Panor introduced some new products, such as the Stereo 70 II. Panor/Dynaco's most ambitious stereo tube amplifier was the Stereo 160, a 75 wpc, all-tube stereo power amplifier with switchable pentode/triode modes, adjustable tube bias potentiometers, and 6550 output tubes.

While Panor owns the Dynaco brand name and trademark, there is no longer any direct connection with the company founded by David Hafler.[1]

Dynaco tube equipment[edit]

Dynaco introduced tube audio amplifiers, tuners, and preamplifiers between 1955 and 1976.

Notes[edit]

References[edit]

External links[edit]

Sours: https://en.wikipedia.org/wiki/Dynaco
Dynaco 400 Amplifier - Restoration and modded

Solid State Power Amp Reviews

One by one, the major amplifier manufacturers have acceded to the pressures of the marketplace and introduced "solid-state" models, whether or not these happened to sound as good as their previous tube-type units. Dynaco was one of the last of the hold outs, preferring, according to their advertisements, to wait until they could produce a solid-state unit that was at least as good as their best tube types. Now, they've taken the plunge at last, with their Stereo 120.

Price-wise and power-wise, the Stereo 120 is the equivalent of a pair of Dyna Mark IIIs, but there the comparison ends. The 120 occupies no more shelf space than a Dyna Stereo 70, it is only about ¾ the height, and it runs as cool as one of Dyna's preamps.

Its 100k ohm input impedance is compatible with the matching requirements of any standard American preamp with the exception of Dyna's own earlier PAM-1, PAS-2, and PAS-3 units, which required matching into 470k or, with a minor modification, into 250k. Conversion kits are available to adapt them to the new arrangement used in the current-model PAS-3X, which is uncritical of output impedance loading.

The Stereo 120 is designed to deliver its maximum power of about 65Wpc channel into a load of 6 ohms, which allows it to feed its rated 60Wpc into either 8 or 4 ohms. Practically all low-efficiency speaker systems are 8- or 4-ohm units, whereas 16-ohm systems (with at least one notable exception, to be mentioned later) vary from moderately to very highly efficient and, hence, will not require the amplifier's full power potential. With a 16-ohm load, the Stereo 120's power capability drops to around 35Wpc, but its low-level distortion characteristic—one of its most unusual aspects—remains essentially unchanged.

Every other transistorized amplifier we have encountered (and read test reports about) hits a minimum of distortion at between 1/3 and 1/2 rated power and then shows a distortion rise below that figure. The Stereo 120's low-level distortion curve is almost exactly like that of a top-grade tube amplifier. Our measurements showed IM distortion down to 0.1% at 1/3 power, and below the 0.06% residual of our IM meter at all levels below about 10 watts.

Listening
The above distortion measurements were made after we had listened to the amplifier at some length, in order not to prejudice our judgment. They confirmed what we heard. This is the only solid-state amplifier we've encountered that does not add a trace of roughness to the sound at low listening levels.

We compared the Stereo 120 with the best of the tube types we could round up: a pair of Dyna Mark IIIs (also 60Wpc), a Dyna Stereo 70, and a Marantz 8B, both of the latter rated at 35Wpc. Speakers used were a KLH Model Nine full-range electrostatic, Janszen Z-600 dynamic-woofer/electrostatic-tweeter system, Acoustic Research AR-3s, Bozak B-310s, and KLH Model Seventeens.

The KLH Nine is rated at 16 ohms impedance, the AR-3 at 4 ohms, and the others at 8 ohms. Hence, the Model Nine system, one of the lowest-efficiency systems available, was operated at a marked disadvantage to the others, in that it was getting only about half of the Stereo 120's rated power capability.

Here's what we found. On the KLH Nine, the Dyna Stereo 70, the Marantz 8B and the Dyna Stereo 120 sounded virtually identical except at levels where some peak clipping started to occur—ie, at levels approximating that of an orchestra crescendo, heard from a row-M seat. At marginal-overload levels, an interesting thing occurred. On program material that was free from high-frequency impulse distortion (as occurs when a phono pickup starts rattling in the groove), the Stereo 120 seemed able to produce slightly higher subjective levels than the other 35W amps without sounding offensive. Thus, in reproducing tapes, for instance, it seemed to have a shade more reserve power than either of the other amps, both of which are actually capable of delivering as much power through most of the audio band as the mismatched Stereo 120. When reproducing discs, though, slight amounts of groove breakup, representing relatively weak but very-high-frequency energy, caused the Stereo 120 to produce noticeably more annoying shatter from the KLH Nines at marginal overload levels than did either of the other 35W amplifiers.

Below the overload point, groove breakup sounded identical—that is, barely noticeable—from all three amps. In this respect, the Mark IIIs did better than any of the other amps, yielding a small but perceptible margin of reserve clean power that allowed us to move from row M to, say, row H without incurring significant peak overload. Bass, too, appeared to be a shade deeper and tighter when the Mark IIIs were used, but at output levels well within the capabilities of the 35-watters, the Marantz and the Dyna Stereo units had a somewhat more liquidly transparent sound.

We are uncertain as to why the Stereo 120 should behave as it did with the KLH Nine, but we're open to suggestions. Meanwhile, suffice it to say that there are other amps better suited for the Model Nine.

On the other speakers tested, it was quite a different story. Here the Stereo 120 was competing with the Mark IIIs on an equal-power basis, and at almost twice the power of the other two amps. Yet the differences noted could not possibly be explained purely in terms of power capability.

For instance, the Stereo 120 seemed able to elicit noticeably deeper, and tighter, bass from all cone-type woofers than did any of the tube amplifiers, although there was less difference between the 120 and the Mark III than between the 120 and the other amplifiers.

Outside of this, the differences noted between the Stereo 120 and the other amps seemed to depend on the complexity of the crossover networks used in the speakers. Except for the low-end improvement, the 120 through the Janszen Z-600 sounded exactly like a higher-powered Marantz 8B or Stereo 70, and was a shade more transparent than the Mark IIIs. The exaggeration of groove breakup at marginal overload was observed from the Janszen Z-600s, but was less pronounced than from the KLH Nines and, of course, occurred at a slightly higher listening level, allowing fairly relaxed listening at row-H levels.

On AR-3s and the big Bozaks, it was hardly any competition. The Stereo 120 seemed to smooth out the response of both of these, making them sound more natural than we've ever heard them. The fact that both are three-way systems, with crossovers, may have something to do with this, but Lord knows why. The KLH 17s seemed a little less forward and somewhat more detailed than before, but except for the low-end improvement, the difference here was slight. In the case of all the dynamic-type speakers, though, the net result was an improvement over the sound from the tube amplifiers.

We have observed much the same sort of improvement when dynamic-type speakers were used with other high-quality transistor amplifiers, but the tendency for those amps to add roughness to the sound at low levels, and to deteriorate over a period of time in normal use, made us hesitant about recommending them. We have no idea how the Stereo 120 will stand the test of time, but it is clear that Dynaco has gone to great pains to ensure that not even the most clod-headed user can damage the Stereo 120. We did our best to pop something, by running the unit continuously at full power and at overload levels, with shorted outputs, partially shorted outputs, open outputs, capacitive loads, and outputs in parallel. The amp made unhappy noises, and it warmed up quite a bit, but nothing got really hot, and nothing let go. If the components will stand the test of time, this should be an extremely dependable unit.

Construction appears to be quite simple and, though we didn't build ours from a kit, we got the impression it would be as easy to put together as any other Dyna power amp.

Conclusion
Summing up, then, we are finally forced to do an about-face on our long-held conviction that transistor amps are not for the perfectionist. Not only does this one seem to have no sound of its own, it also makes most loudspeakers sound better than do tube amplifiers. This kind of performance, finally, justifies switching from tubes to transistors. It's a sad commentary on the industry that the justification had to come three years after the switch.

Sours: https://www.stereophile.com/content/dynaco-stereo-120-transistor-power-amplifier

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