Vintage Brute-70 (40411) clone

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All,

Picked up a heavy black box in a garage sale. It did look like an audio amp and after googling a bit on 'power amplifier 40411' (lots of references to the Tigersaurus found), it turns out to be a european clone of the Brute 70 amplifier as described by E.G. Louis in Popular Electronics, February 1967:

http://www.swtpc.com/mholley/PopularElectronics/Feb1967/PE_Feb1967.htm

I wonder whether it makes sense to bring it back to life. At least one of the rectifier diodes have died and the 40411 output transistors might have given up, too.

The only documentation is a tiny schematic where a few components are added by hand, presumably to make it more stable (see attachments). The schematic looks like it comes straight from an Application Note, presumably from RCA. The PE article mentions Data Bulletin ATC-408, but I have been unable to find that one. Any pointer appreciated.

Yes, the box is rather european with it's mains voltage selector (from 110 to 245) and DIN input connector.

BRs,

Jacques
 

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RCA Application Note/ Data Bulletin ATC-408

No, I wasn't expecting Nirvana from this unit, but I was just curious about it's origins. Bringing it back to life shouldn't be too expensive, it turns out that one of the big 4700 uF capacitors was short-circuited (leaked), probably caused the faulty rectifier.

It is more the experience of "how does it sound" I'm after, so I try to put it back in reasonable state, but I'm less interested if it's going to blow a few decent tweeters because it oscillates all over the place :) That's why I was asking if anyone has the RCA Application Note.

Of course, it has a hefty mains transformer (2 x 30 V AC secondary) and a solid chassis. After I have heard it (and possibly blow a tweeter or two,) I will very likely consider recycling it for a Destroyer X or similar.

Cheers,

Jacques
 
Re: RCA Application Note/ Data Bulletin ATC-408

jacques54 said:

It is more the experience of "how does it sound" I'm after, so I try to put it back in reasonable state, but I'm less interested if it's going to blow a few decent tweeters because it oscillates all over the place :) That's why I was asking if anyone has the RCA Application Note.
Cheers,

Jacques

If it still has the 40411's you may very well blow tweeters if you go 'blasting' it. Probbaly won't oscillate at normal signal levels, but very well could when clipping. Those old RCA outputs had issues with sticking and common mode conduction - especially the "PNP" side.
 
This is absolutely sure a Carad AAS140 amplifier!
Carad was a Belgium high end audio manufacter till the early 70's.
I have used these amplifiers some 40 years ago - it was in those days the defacto standard DJ amp.
Should have somewhere one, but mine is not so clean as the one on the pictures.
You should not canibalize it - it's a piece of electronic archeology:)
 
This is absolutely sure a Carad AAS140 amplifier!
Carad was a Belgium high end audio manufacter till the early 70's.
I have used these amplifiers some 40 years ago - it was in those days the defacto standard DJ amp.
Should have somewhere one, but mine is not so clean as the one on the pictures.
You should not canibalize it - it's a piece of electronic archeology:)

Thank you for this advice. Can you post an originale broshure from Carad's AAS140 ??
I can't open the URL
http://www.gloeidraad.nl/radioforum/index.php?id=5880

I like such circuits, because until now nobody was able, me to prove, that a modern amplifier circuit blown away clearly this old topology as showed here (from the audible view, not from the view of THD-values), if both topologies are working on a power supply of the same quality.
And the reason therefore is clear for me in the meantime:
Independend of the efforts and complexity by the "front-end" - by idle currents arround 20-50mA through the output stage there is always a limit by the maximum achievable audible sonic quality causes complex THD character. Only by Class-A the acoustical enhancement between an ordinary and a nearly perfect front-end is audible.
By post #13 about
http://www.diyaudio.com/forums/solid-state/99967-anybody-have-scan-483b-motorola-2.html
you will find a similar topology - the power amplifier project "Black Devil" (from German's vintage magazine "ELRAD").
 

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Well, yes, it's an AAS140 because that's what is printed on the back cover... I only wanted to reach a copy of the application note that Carad was using to implement an amplifier.

Thank you for this advice. Can you post an originale broshure from Carad's AAS140 ??
I can't open the URL
Nederlands Forum over Oude Radio's - Artikel over Carad AAS26/PPC27 buizenversterker?

This URL points to a question about the combination Carad PPC27/AAS26, a tube pre/power amplifier from between 1961 - 1967. That's a circlotron circuit with EL84 (6BQ5), 2 x 12W RMS.

The only brochure I have seen of an AAS140 shows a small photograph where you see even less than on these photos. The characteristics state 2 x 70W RMS into 8 ohms, but I'll have to look up my scans in order to show this and to tell more...

BRs,

Jacques
 
[...] The only brochure I have seen of an AAS140 shows a small photograph where you see even less than on these photos. The characteristics state 2 x 70W RMS into 8 ohms [...]

Here is the page and the (small) description at the bottom right.

The page shows more interesting things IMHO, like the "Pro Arte" radiogram with a Thorens TD124. There are also "Louis XIII" and "Louis XV" television sets, from way before the French revolution, I'd think
:)
 

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Hi

This RCA circuit is a fascinating exercise in how not to design an amplifier. There are so many things wrong it is hard to know where to start. Probably the most important change is to recycle the 40411's as these were slower than 2N3055's. They could not even, in this circuit, drive 20kHz without "latching up". Not a real latch up, but with 100 ohms base-emitter resistor they are not turned off quick enough so they stay conducting in Class A, and keep powering on perhaps until something gives. At a push, you could change the 100 ohm base resistors for 10 ohms. This in simulation at least turns the devices off at 20kHz and keeps them from steaming. Better, use newer epi transistors like the MJ15003 (and complement if you like).
Of course the zero-balance control works from the output base resistor and is another BIG PROB. Because this is biased from a diode working in Class B its bias will change with signal. This will add its own bass line to the music it is playing.

So by the time you've sorted this out it is possible to change the input to a regular differential input pair, add a current mirror and then the 40407/40408 pair in the VAS will work much like a Blameless amp!

But it should be possible to add a few transistors in TO-92 cases to the PCB as these don't take up much room.
 
Hi schematic of this Amp look the same like magic music active speakers Tri-amp Braun LV1020 start build from1970 and up. if somebody have experience and know how play Braun LV1020 understand me. I try compare sound of Braun with High End modern very , very expensive speakers and amp , make appointment and visit stores just listening top of the line and big $$$ different speakers with gorges amp . I don't know , after visit I was shocked how can deadly play expensive toys , and the same time I was very happy , because I have perfect sounding my stereo.
 

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I have seen a very close copy of this circuit many times it was used in the 100 watt WEM power slaves that were made in the early 70,s
I have repaired a few of them they were normally used in stacks fed from a WEM
band-mixer
I can remember having a right tussle with on of them it turned out to be an oc diode not the bias one but the offset 1
Trev
 
I have seen a very close copy of this circuit many times it was used in the 100 watt WEM power slaves that were made in the early 70,s
I have repaired a few of them they were normally used in stacks fed from a WEM
band-mixer
I can remember having a right tussle with on of them it turned out to be an oc diode not the bias one but the offset 1
Trev

They were used as a pa by bands such as the cream I have met with Charlie Watkins of WEM and he was kind enough to tell me about those magical days of rock and super groups where his concept of slave amplifiers was the only way to reach large audiences
As to be all that is wrong with audio amplifier design I feel you need to look a little closer RCA did not employ clowns
Trev
Trev
 
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