| THE HISTORY AND FUTURE OF DYNACO TUBE AUDIO by Charlie Kittleson During the mid-Fifties, hi-fi and the kit building craze was at its peak. Many music lovers wanted to build their own hi-fi sets because factory built equipment was expensive. Some audio enthusiasts opted to scratch build their equipment using circuits from published articles in Audio magazine or Radio-Electronics. For others with less electrical and mechanical ability, a kit amplifier was more appealing. Thus the demand for audio kits began. David Hafler, the founder of Dynaco, got his start in the world of commercial audio by partnering up with Herb Keroes in the late 1940's. The two formed a Philadelphia, Pennsylvania company called Acrosound in 1950 to build high quality audio output transformers. By 1952, they had developed and marketed the famed "Ultralinear" circuit. The Ultralinear circuit topology was originally patented in the late 1930's by Blumlein in England. In the early 1950's, push-pull class A triode amps were the "high-end" choice. Their major drawback was low power, usually only 10-12 watts using a pair of 2A3s. Tetrode and pentode push-pull designs were more efficient and powerful in class AB-1 mode. Using the 6L6, KT-66 or 807, an amp designer could get between 20 and 40+ watts. Major drawbacks of these were higher odd-order distortion than triodes and high output impedance, producing low damping factors. The output impedance and distortion could be reduced by feedback, but this required a high quality transformer and still left the amp with a "pentode" sound. To reduce this distortion, Hafler and Keroes used the Blumlein circuit and a proprietary output transformer with a patented 43% Ultralinear ratio that achieved the power of a beam tetrode circuit and reduced distortion to that of triode amps. The output transformer was equipped with taps for the screen grids with a reduced turns ratio which ran the output tubes part way between the triode and pentode connection. In the mid to late 1950's, the Ultralinear circuit and transformer became very popular and was used by many start-ups and established hi-fi manufacturers. EICO, Heathkit and other manufacturers offered Acrosound output transformers as a premium upgrade for their amp line. In 1954, the relationship between Keroes and Hafler began to wane, so they parted ways and Hafler formed his own company - DYNACO. Hafler's goal was to produce an affordable amp with high quality transformers, a stable circuit, high power, easy to assemble and affordable. In 1955, the first Dynaco amplifier was introduced - the Mark II. It was a 50 watt amplifier using the patented tapped screen-grid output transformer (A-430 with 4 and 16 ohm taps), push-pull Mullard EL-34 tubes, and a single 6AN8 tube with the triode portion used as a cathodyne phase inverter and the pentode section used as the driver. The rectifier was the popular 5U4G. The Mark II was unique in a number of ways. First, it was available in either assembled or kit form under the "Dynakit" name. Second, the entire driver and front-end circuit were pre-built on a printed circuit board. Third, it was low priced - $59.95 in kit form and $79.95 assembled for a 50 watt RMS power amp - complete with all tubes and a protective cage. The chassis was cadmium plated steel and the case was perforated steel, painted black. The amp was a success and was sold through the early 1960's. Also in 1955, Dynaco introduced their first preamp, the PAM-1 ($34.95), that required a separate power supply or could be powered by the octal power out socket on the Mark II amp. The preamp was very compact and unobtrusive. It featured controls for volume, bass, treble, function selector and phono equalization. Tube compliment was two 12AX7/ECC83 dual triodes, typically Mullard or Telefunken. These brands were chosen for smooth sound, low microphonics and long life. The unit was packaged in either a dark gray or ivory enameled sheet metal case with lacquered brass face plate and white plastic knobs. The PAM-1 was available through the early 1960's. In 1957 McIntosh, Fisher and Scott sold 60+ watt power amps. Not to be outdone, Hafler introduced the Mark III amp in 1957. It was the first commercial US amp to use the new KT-88 power tube from Genalex of England. It produced a solid 60 watts RMS and used the same 6AN8 driver/phase inverter circuit from the Mark II. Changes included the use of a 5AR4/GZ-34 slow warm-up rectifier tube, higher voltage (500+) power transformer, newer output transformer (A-431 with 4, 8 and 16 ohm taps), beautiful nickel plated chassis, and a heavy gauge perforated steel cage finished in dark gray. The amp sold for $79.95 in kit form and $99.95 assembled. It was an instant success and was used in more systems than probably any tube mono power amplifier. It is estimated that several hundred thousand Mark III's were made from 1957 through 1977, its final year of manufacture. Early versions used cloth covered wire on the transformers that had gray painted end bells. Later versions, in the 1970's, had a different variant output transformer (Z-216) and a power transformer using plastic-insulated wire. The cage and transformers were finished in gloss black. It should be noted that using 6550As in place of KT-88s in Mark III amps may cause thermal runaway. (The grid resistor in stock Mark IIIs is much larger than the value specified for the 6550A.) Dynaco used Tresco, a Philadelphia, Pennsylvania transformer manufacturer as the source for most of their transformers. In the mid-1960's Dynaco used Japanese sources for their power transformers (tar/epoxy dipped) and some output transformers. After the explosion of the television industry in the post-war era, more interest was focused on FM radio. To respond to the public's needs, Dynaco introduced the FM-1 ($79.95) in 1957. It was a monophonic tuner available in assembled or kit form that was relatively easy to build and align. The case was gray or ivory enameled sheet steel with a lacquered brass faceplate. In the late 1950's, stereo records became available and the need for stereo playback equipment began to grow. Many audiophiles just bought a stereo phono cartridge, another amplifier and another speaker to play their records and tapes in living stereo. Dynaco's first stereo component was the PAS-1. It consisted of two PAM-1 preamps and a passive stereo adapter box. All three items were attached to a large brass faceplate. Power was supplied from the octal power sockets from either Mark II or III amps. This setup was a maze of cords and interconnects and was only available for a short time. Dynaco saw the need for a single chassis stereo power amp, and in 1959 introduced the legendary Stereo 70. The amp originally sold for $99.95 in kit form and $129.95 assembled. The entire front end circuit for both channels was mounted on one printed circuit board. The circuit consisted of a 7199 tube used as a driver/phase inverter for each channel. The 7199 was introduced by RCA in the late fifties specifically for audio applications but was similar in construction and characteristics to a 6AN8. The output stage was push-pull EL-34 Mullard or Amperex beam tetrodes. Output transformers were the famed A-470 Ultralinear type and were rated at 35 watts RMS/channel. There were several variations of the A-470 transformer over the years including those with cloth lead wire, plastic lead wire and different stack densities. The power supply used a GZ-34/5AR4 and a large power transformer which also had a number of variations over the years. Early Stereo 70s had nickel plated chassis and later ones were chrome plated. The cages were originally brownish-gray perforated steel. Later versions were grayer in color and the last ones had black cages. There were probably more Stereo 70 amps manufactured than any other stereo power amp. Some estimates are that almost 500,000 units were produced. The Stereo 70 is also the most modified and upgraded amplifier in existence. Probably more Stereo 70 amps have been passed on from father to son than any piece of audio equipment. It is easy to improve the amp with an upgraded driver board and beefier power supply. There are thousands of Stereo 70s in service today. In fact, there have been two re-releases of the amp in the late 1980s and early 1990s. As a match to the Stereo 70, Dynaco introduced the PAS-2 ($59.95) stereo preamp in 1959. The PAS-2 eliminated the need for separate mono preamps and stereo adapters. It was a complete, low cost stereo control center in one compact box. The majority of the circuit was on two printed circuit boards ?one for the phono stage and one for the line stage. Tube complement was four ECC-83/12AX7s (typically Telefunken smooth plates) for the phono and line stages. The rectifier tube was the 12X4. Filaments were run from DC and rectified by a selenium stack. (Note: the selenium rectifiers deteriorate with age and must be replaced with silicon diodes for optimum performance). The faceplate of the PAS-2 was lacquered brass, the case was either dark gray or ivory white and the knobs were brown plastic with brass colored inserts. In 1960, the Mark IV ($59.95) 40 watt power amplifier was introduced. It was aimed at the audio purist who wanted the performance of a mono amp using the Stereo 70 topology. The Mark IV was identical in most ways to the Stereo 70 including front end circuit, push-pull EL-34 output stage and the A-470 output transformer. Differences were the power transformer, smaller than the Stereo 70's, but with higher plate voltage and different packaging. Mark IVs will actually put out about 44 watts RMS. The amp is rectangular in shape and was not made in large numbers. It too, is an excellent candidate for modifications or upgrades. In 1964, Dynaco changed their front panel design. The PAS-3 ($69.95) was equipped with similar circuitry to the PAS-2, but featured an aluminum champagne anodized faceplate and all-metal knurled knobs. In 1966, the PAS-3 was replaced by the PAS-3X featuring a different tone control circuit. The PAS-3 and PAS-3X were available in assembled or kit form and were made through 1977. There are probably more PAS-3s than any other tube stereo preamp. In the late 1980s Dynaco introduced a re-issue of the PAS-3 with different topology and power supply. In late 1961, when the FCC approved a standard FM multiplex stereo broadcasting system, many hi-fi manufacturers released FM stereo tuners, receivers and stand alone multiplex adapters to convert FM mono tuners. Dynaco upgraded the FM-1 to the FM-3 and included an on-board multiplex system to receive both mono and stereo broadcasts. They also introduced a multiplex upgrade kit for the FM-1, the FM-3X. The FM-3 ($109.95) was available in assembled or kit versions and was produced through the 1960s. The faceplate was champagne gold aluminum with metal knurled knobs. Stereo "bookshelf" integrated amps were very popular in the early 1960's because they were simple and used up little space. Dynaco introduced the SCA-35 ($99.95) integrated amp in 1962. It produced about 17 watts per channel and was very popular with music lovers and record collectors. The circuit featured two 12AX7s for the phono and line stages, two 7199s for the driver/phase inverter stages and four EL-84/6BQ5s for the output stages. The rectifier was solid state. The output transformers were very high quality units (Z-565) and are thought by some to be the best sounding Dynaco output transformers. For audio enthusiasts who wanted the sweet sound of EL-84s, Dynaco produced the ST-35 ($59.95) basic power amp (no photo). It produced 17.5 watts per channel and used a 7247 driver/phase inverter and push-pull EL-84/6BQ5s. The rectifier was solid state. The chassis was cadmium-plated and cage was gray perforated sheet steel. The ST-35 is very popular for bi-amping horns because of its sweet and smooth characteristics. Very few ST-35s were produced and they are quite scarce. In the mid-1970s, Dynaco moved their design and manufacturing facility to Blackwood, New Jersey and expanded production there. The later versions of the Stereo 70 and the Mark III amps with black cages were produced at this location. The Mark VI (no photo) was the last all tube amp to be produced by the original Dynaco. It was introduced in the mid-1970s and aimed at the Japanese tube audiophile market. It produced 120 watts RMS and used four type 8417 beam power pentodes. The driver/inverter tube was the 7199. A biasing and output meter was on the front panel which was black anodized aluminum. The power and output transformers were massive and the rectifier was solid state. Some experts claim that only 1000 Mark VIs were produced. Most of the Mark VIs were not assembled at the Dynaco plant, but were sold unassembled to Stereo Cost Cutters (now Sound Values) and other companies who sold them as kits or assembled. In the mid-1960's, Dynaco began producing solid state amps and preamps which we will not cover in this article. In the late 1970's David Hafler sold Dynaco to TYCO Industries, a toy manufacturer. He then started another company called Hafler and sold solid state amps and preamps. Stereo Cost Cutters of Ohio bought a huge stock of inventory from Dynaco's Blackwood, New Jersey facility. They sold parts, tubes and some un-assembled kits. They also re-designed the PAS-3 preamp and Stereo 70 power amp in the late 1980's. In the early 1990's, Panor Corporation of Hauppauge, N.Y. purchased the Dynaco name and began selling Dynaco-branded solid state amps and preamps. In 1991, they designed and produced an all tube preamp, the PAS-3, Series 2. In 1994, they introduced the PAS-4. and the Stereo 80 all tube power amp. These new products were designed by John Nunes and Arn Roatcap, previously of MFA. Dynaco will be introducing the PAS-5 all tube remote control line stage only preamp in mid-1995. They recently introduced a tube type compact CD player and will be introducing the Stereo 160 power amp soon. The warm glow of tubes is now alive and well at at Dynaco. |
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