Magazine Search

[Dean Huster]

OK, trivia nuts. For many years, McGraw-Hill published an industrial magazine titled Electronics. During the 1970s and other years, they had a department similar to Penton's Electronic Design's "Ideas for Design" where readers submit cute design ideas to be shared with others. I'm hunting for a specific such submission that was published sometime between about 1970 and 1972, most likely 1971. The reader submitted an audio power amplifier design that involved about 4 small-signal transistors and a pair of 2N3055 power transistors for the output. It used a clever circuit to develop the differential signal required by the output using a 741 (hey, this was around 1971, OK?) with the output pin connected to a do-nothing resistive load -- the two output signals were derived from the two power supply pins which were in series with a low-value resistor which was then connected to a decoupled power supply. This thing had pretty impressive specs with around 120W rms output, DC to at least 200KHz and low distortion. Overall, the circuit was relatively simple. I'd like to find this article.

I can't find a spot on the Internet having a database of Electronics articles. One possibility is to go to a large technical library such as that at the University of Missouri - Rolla (their engineering campus) and see if they have ancient bound copies. Another is to see if any of you have a collection and could find the article and copy it for me. Another is to see if Penton Publishing, who bought the title from McGraw-Hill can be of any help.

Any ideas out there?

 

[dr pepper]

Theres another version, I think later using I think a ne5532.
To be honest the number of audio amp articles in electronics mags would make it difficult to find.

 

[jpanhalt]

Rather than go all the way to Rolla, I would try an interlibrary loan from the closest college library (Poplar Bluff?). Even at Rolla, I suspect such old, bound issues are in storage off site.

Another choice is the Library of Congress. I once had to go there for some obscure publications. That is a bit further trip, though. Does the Harviell airport have jet traffic?

John

 

[KMoffett]

They used to periodically publish magazine size paperback books with the "Ideas for Design". I think I have some from around that era. (God, I'm such a pack-rat)
I'm at the Oshkosh EAA Air Show right now, but will check when I get home on Friday. Love the smell of Jet-A in the morning!

Ken

 

[strantor]

I seem to have found the magazine here but I cannot view the pages for the circuit you're looking for.
If that's not the right one, try searching "electronics volume 43" or "electronics volume 45"

 

[audioguru]

Audio goes up to 20kHz and more.
But a lousy old 741 opamp and 2N3055 transistors have trouble above only 9kHz. The 741 opamp has too much b[]hissss[/b] for audio.

A 120W into 8 ohms amplifier needs a supply of about plus and minus 45V or more which will destroy lower voltage 2N3055 transistors.

 

[atferrari]

Time ago...

Hola Dean,

In 2006 Audioguru suggested to you a similar circuit published in a site (or forum?) "something" LAB IIRC.

 

[k7elp60]

Dean,
I have a couple of schematic's near what you describe. Both of them require a split supply, that is + and - with a ground. If this sounds right I can scan them and post them here.
Ned

 

[KMoffett]

Sorry, don't think my collection will help. I have six issues of "Electronics: Designer's Casebook" that go back to ~1976.

Ken

 

[Dean Huster]

That's it! "Designer's Casebook". And 1976 would be too late to pick that one up. Graff et.al. did those "circuits" books and I have a few. It was pretty cheap, clueless authoring -- copy all the skem yhou can find and publish them in a book.

I want that circuit for personal reasons, so really don't require technical criticism since it's an ancient circuit ... the 741 hadn't been out that long in 1971. A CTMCS I worked with at the Naval Security Group Activity, Sabana Seca had built it in 1971, and I helped him to check it out since I had the equipment in the cal shop. We put a function generator to the input of this DC-coupled amp and the biggest speaker we could find on the output just to see what it did near-DC. That speaker was the typical 3.2 ohm table radio speaker, not hardly a match for the amp in power. We'd never seen a speaker cone "breathe" before and at a 1 Hz frequency, it amazed us. After playing with the thing for 15 minutes or so, the Chief went to disconnect the speaker and burnt his fingers on the yoke. Being a seasoned Navy Chief with 20 years in, his comments upon being burned were very educational, even to the the rest of us sailors. The voice coil, of course, had turned into a heater, sent the yoke to ungodly temps and totally wrecked the speaker. I'm surprised the VC didn't open. He had already put a low-pass filter in the circuit to keep the amp's bandwidth confined to 100KHz ... otherwise it made it to 500KHz or so at the -3dB point.

Does the Harviell airport have jet traffic?

Ha!!! That's funny! Nearest "airport" is a grass strip for crop dusters. Harviell is a whistle stop on the Union Pacific. Poplar Bluff, 12 miles north of us, just increased runway length to handle the little business jets, but there's no scheduled airlines. If there was, you can bet the down here, they'd get a gun pulled on them if they told you at the airport to take your shoes off and walk through a security gate. That was after they told them where they could put their airplane and how far up.