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36-459: 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

72-465: A tetrode or pentode vacuum-tube (also called "electron-valve") to a load (e.g. to a loudspeaker ). 'Ultra-linear' is a special case of 'distributed loading'; a circuit technique patented by Alan Blumlein in 1937 (Patent No. 496,883), although the name 'distributed loading' is probably due to Mullard . In 1938 he applied for the US patent 2218902. The particular advantages of ultra-linear operation, and

108-466: A diamond shape (centre-front, centre-left, centre-rear, centre-right). Initially (first available in 1969 with th Dynaco SCA-80Q amplifier ), it was introduced as a derived (2:2:4) four channel "decoding" system based on the Hafler circuit , where the back channels played ambient sounds recovered from standard stereo sounds. As such it wasn't used initially used as an encoding method (a similar approach

144-507: 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

180-626: 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

216-507: 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,

252-521: 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

288-730: 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 . Critical reviews of

324-448: 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),

360-419: A system. Dynaco sold this matrix circuit ( Dynaco QD-1 Quadaptor , introduced in 1971 )with a large and triple high-wattage potentiometer inside. Electronic amateurs could build the circuit much more cheaply – e.g., with a four-position switch (four steps in level of the rear sound from min. to max. level) using fixed resistors of, for example, 20, 10, 5 and 0 (short-circuit) ohms. Because, in practice, only

396-466: 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

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432-420: Is found to fall to an unusually low value—sometimes less than for either triode or pentode operation —while power efficiency is only slightly reduced compared with full pentode operation. The optimum percentage-tap to achieve ultra-linear operation depends mainly on the type of valve used; a commonly seen percentage is 43% (of the number of transformer primary turns on the plate-circuit) which applies to

468-411: The 1980s. The Dynaco A-25 model proved to be extremely successful, selling between 600,000 and 1,000,000 units. A modified aperiodic bass reflex design using SEAS speakers in a handsome wood cabinet, the A-25 sold for $ 79.95 each in 1969 making it competitive with much more expensive loudspeakers. The patented aperiodic (essentially non-resonant) woofer design utilized a highly damped vent instead of

504-719: 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. Dynaco introduced tube audio amplifiers , tuners, and preamplifiers between 1955 and 1976. Ultra-linear Ultra-linear electronic circuits are those used to couple

540-614: The KT88, although many other valve types have optimum values close to this. A value of 20% was recommended for 6V6GTs. Mullard circuits such as the 5-20 also used 20% distributed loading (but did not achieve ultra-linear operation), while LEAK amplifiers used 50%. The characteristics of the circuit which make distributed loading suitable for audio power amplifiers, when compared to a triode, beam tetrode or pentode based amplifier, are: The distributed load circuit may be applied to either push-pull or single-ended amplifier circuits. Note that

576-533: 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

612-596: 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

648-507: 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

684-506: The ST 70 the most popular tube power amplifier ever made. 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

720-425: 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

756-565: The cathode has a portion of the output signal applied to it, and was referred to as "distributed load" by Peter Walker of QUAD. In the United States, McIntosh Laboratories used this technique extensively in their vacuum-tube power amplifiers. Audio Research Corp have also used a similar circuit. Dynaquad Dynaquad , or DY , was a matrix decoder 4-channel quadraphonic sound system developed by Dynaco in 1969. The system originally had four speakers that were arranged in

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792-538: The company moved its business operations to 3912 Powelton Avenue in Philadelphia, where they remained for several years. 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

828-467: The format. The competing Stereo-4 system was very similar and can be considered as compatible, as both use very similar decoding matrixes (based on the Hafler circuit ). The left and right rear speakers are connected to the two-channel stereo amplifier via a passive matrix circuit, while the front ones stay directly connected to the amplifier. A lot of stereo material, recorded with a central, non-directional microphone (kidney pattern) placed in front of

864-557: The highest level was of any use, a more basic set-up with only the fixed 10 ohm resistor at close-to-zero cost is possible. The system requires relatively flat impedance curves for the rear speakers to work properly, which was often the case in the tube-amplifier days. Tube amplifiers had a constant impedance over a wide range, and worked best with high-efficiency speakers. Later on, when transistor amplifiers were used, speakers tended to lose that design feature. (Lower impedance meant higher power output for these amplifiers, compensating for

900-464: 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

936-464: The lower efficiency of such designs.) The system worked best using a transistor-based stereo amplifier, low-efficiency front speakers, and high-efficiency, constant impedance rear speakers. The encoding was unusual in that, like the Stereo-4 system, it did not use 90° phase shifters. During 2016, recording engineer Stephen Desper in several online forum posts publicly refuted the common rumour that

972-451: The name itself, were published by David Hafler and Herbert Keroes in the early 1950s through articles in the magazine "Audio Engineering" from the USA. The special case of 'ultra linear' operation is sometimes confused with the more general principle of distributed loading. A pentode or tetrode vacuum-tube (valve) configured as a common-cathode amplifier (where the output signal appears on

1008-512: The new audio speakers were not favorable, and they disappeared from the market in the mid-1980s. 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 Values and Sound Valves). In 1991 the Pan Orient Corporation (later Panor Corporation ) acquired the Dynaco trademark, and in 1993 began marketing electronic audio components with

1044-413: The orchestra, possessed suitable phase difference stereo signals. When taken from this passive speaker matrix for the rear channels, they produced a quasi-quadraphonic effect at low cost (the patent specifies the use of one fixed 10 ohm resistor and three variable 20 ohm resistors in a star arrangement). Especially for classical music, a fine impression of concert-hall ambiance is achieved with such

1080-406: The plate) may be operated as: The impression of any portion of the output signal onto the screen-grid can be seen as a form of feedback, which alters the behaviour of the electron stream passing from cathode to anode. By judicious choice of the screen-grid percentage-tap, the benefits of both triode and pentode vacuum-tubes can be realised. Over a very narrow range of percentage-tapping, distortion

1116-507: 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

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1152-414: The term 'ultra linear' was expressly reserved only for the condition of optimum tapping point. As Hafler and Keroes wrote: " Our patent claims cover the use of any primary tap in this circuit arrangement. However, we have restricted the use of the term "Ultra Linear" to the conditions where the dynamic plate characteristic curves are most linear ". The "QUAD II" amplifier from QUAD uses a circuit in which

1188-574: 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

1224-399: 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

1260-496: 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,

1296-575: Was used on the Electrovoice Stereo-4 system). A simpler form of Dynaquad was adopted, allowing an easy adaptation of existing home setups. The two forward speakers remain in their normal positions, with the user only needing to add two similarly positioned back speakers, forming a square (front-left, front-right, back-left, back-right). Four channel record pioneers Vanguard Records started to use it as an encoding/decoding matrix (4:2:4 format) in 1971. There were few albums released in

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