Acoustech Stereo Amplifying System?

So I go out to this guys place following a line on some possible gear. I was told he had a couple of things he wanted me to fix and I could just take the rest. It turned out to be pretty much a complete bust. The stuff that I could just take was total junk. The rest was either stuff he wanted to keep for himself or average stuff that he wanted stupid prices for.

This Acoustech was one of the ones he wanted to fix. I've never seen one before, or even heard of the brand.



The front panel is champagne gold, so the yellow look is not entirely due to my bad lighting. It's not just an amplifier it's an "Amplifying System". Nice chunky metal knobs, the orange plastic push buttons look out of place next to them.



It is constructed on edge cards in point to point wired backplane. It's a bit hard to see in the picture, but all the transistors (except the outputs) are in sockets. Cards and socketed transistors are something I expect to see in old test equipment, not an amplifier. All the transistors are RCA Germanium.



Well, this was one oddball that went back to where it came from. I lost interest in it myself when I saw the Germanium transistors.

Anyone else seen or owned one of these or any other Acoustech gear?

Mid-sixties, early transistor gear. Note the transistors are in sockets rather than soldered directly to the boards. Lafayette has 'em in their '66 catalog.

US-made, I believe. Other than that, I know nothing about them.

Can you say AR? This is obviously from the same factory that built the AR integrated amp. How well I remember the Doors 20th Century Fox at 10pm thru AR 4x speakers, Dual tt, and the AR amp.

Acoustech amps. Is this one still around?

Wow! I bought one of the integrated amps when they first hit the shelves in about 1966 or 67. They looked like miracles, all in one amazingly light package with 30 watts per and a dampening factor of around six million. Sounded great but blew transistors like watermelon seeds.

Germanium transistors-- what's wrong with them?

Steve

Early SS pioneer company that put out some nice products. Having no experience or other designs to draw from there were early problems that the company worked out as they were discovered to the point that the later productions were pretty reliable. Admittedly, throughout the lifespan of the germanium transistor as the predominant device device failure was an issue. More an issue of the device than the circuit design.

The also made a preamp and power amp. Most of them on the market today have seen hard use and the faceplates have not weathered well.

The company was eventualy bought out by Koss from memory and it produced the lineup under its name for a period about the time that the company was producing the Koss 1 speaker.

Take some time to bring it back, do not push it hard, keep the speaker load at 8-16 ohms, the high side better and not too complex a load and you should be happy.

There is Acoustech equipment in the late 1960s Allied and LRE catalogs I have. I can post some scans sometime later this weekend if anyone's interested.

Looked like pretty serious stuff.

For anybody wondering, Acoustech was founded out of Ann Arbor, MI by a former DCM employee, Tom Munsell. He just recently passed away two weeks ago.

I picked up a tuner / amp set over a year ago from a yardsale here in my town. These were built in Cambridge Massachusetts. The guy i got it from wrote / laid out the manuals for these. I was under the impression mine (since sold) were rather early; guess the orange buttons were an upgrade!
JimB

http://www.audiokarma.org/forums/showthread.php?t=183593&highlight=Acoustech

This is an Acoustech VII that I have restored : http://www.dcx2496.fr/acoustech.php.

I wrote a little note about Acoustech history and Arthur A. Janszen, father of KLH (in french, sorry, use Google translation tool)

http://translate.google.fr/translat...tp://www.dcx2496.fr/acoustech.php&sl=fr&tl=en (some silly sentences to be expected)

A picture says it all :

This is very cool equipment.

hockeye said:

Wow! I bought one of the integrated amps when they first hit the shelves in about 1966 or 67. They looked like miracles, all in one amazingly light package with 30 watts per and a dampening factor of around six million. Sounded great but blew transistors like watermelon seeds.

Germanium transistors-- what's wrong with them?

Steve

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Germanium transistors whether in small signal or power devices were available before the silicon transistor took over the lead. Silicon could take higher temparatures than germanium so development favored the new, and eventually took over most new devices. Acoustech, in addition neglected to address the issues of excessive currents in driving loudspeakers, apparently designing their amplifiers assuming resistive loads. But since loudspeakers have large variations in impedance and work more like motor/generators rather than simple resistors. Their only method of protection against improper loads and short circuits, was a fuse. Usually the fuse would outlast the more fragile power transistor. And if it was substituted for a smaller one, one would have to keep changing the fuse whenever a crescendo was encountered. Acoustech as an amplifier, never survived the grade.

Wayne Chou

I "believe" the Acoustech was promoted as being the "FIRST" all transistor stereo amp.

Anyone on this old thread know where I could find a schematic for this Acoustech integrated amp?

Sanfansui said:

Anyone on this old thread know where I could find a schematic for this Acoustech integrated amp?

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AUDIO Magazine has a write-up of the Acoustech I power amp in January 1963. "Design of Solid-State Stereo Power Amplifier with Silicon Transistors." Marshall R. Myers, Jr. & Morley D. Kahn, AUDIO, pp. 21-24, 31, 60.

Once the 2N3055 became available, R. R. Moore says he was inspired (in November 1964's AUDIO Magazine, pp. 19-21 and 87-88) to distill the Acoustech I and the GE app notes designs, and he created the "El-Cheapo 2-30". In March 1966 (Fig. 11 on p. 416 of RCA Transistor Manual SC-12) RCA introduced a similar "A High-Quality 10W Audio Power Amplifier", which dispensed with their usual interstage phase splitting transformers driving stacked 2N2147s (Fisher, Heathkit, etc).

These designs originate with H.C. Lin's direct-coupled design from 'Electronics', September 1956. Lin was with RCA when he wrote it before moving to CBS-Hytron north of Boston. Dwight V. Jones, the 'Hi-Fi guy' in Electronics Park in Syracuse (General Electric applications engineering department) continued to refine these designs as new transistors were developed. In 1963 Acoustech appears to have commercialized the latest 6th Ed. GE design to a high-power level via expensive custom silicon transistors (designed by Transitron of Wakefield, MA, the article states that the commercial equivalent to those custom ST7175 cost well over $20 each in '63 and some cost as much as a whole, presumably low-cost, vacuum tube amplifier).

See the GE Transistor Manual 6th Ed (1962) Fig. 9.15, p.137, topologically very similar. GE 7th Ed (1964) Fig. 11.40, p. 269 adds a buffer stage with gain (unlike the unity gain of the Acoustech) and replaces the 0.47 ohm emitter resistors with fuses.

Once the 2N3055 arrived, it enabled the cost-effective and widespread acceptance of transistor audio power amplifiers, via the non-interstage-transformer (direct-coupled) gain block, with quasi-complementary silicon outputs, using single-ended capacitive coupling to loudspeakers.

Quad developed their output-triple topology in 1967, providing greater linearity with only NPN Si outputs. RCA would show true complementary-symmetry in August 1967 (RCA Transistor Manual SC13) with some interesting new wrinkles. Radford commercially introduced complementary-symmetry silicon outputs in 1968 with the new Motorola NPN/PNP Si output pair. RCA in 1969 developed the differential-input output capacitorless dual-rail design, first using quasi-complementary with a Baxandall diode.

Rapid progress over the first few years of solid state power amplifiers converged on the RCA differential topology and variants of it are likely the most widely used across the world, to this day, for analog solid-state audio power amplifiers.

We would do well to provide this Acoustech more historical publicity with its advertising focus on robust power supplies, dynamic power reserve, clean transients and overload, extended frequency and phase response and relative lack of low-level crossover distortion, a solid 10 years before slew-rate-limiting ('TIM') became more widely known.