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Old 28th December 2011, 11:46 AM   #1
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Default VINTAGE AMPLIFIERS ( The ultimate thread )

happy new year every one !!!

This thread is a actually a copy of an existing thread in a Greek forum .Obviously the thread is there to inform and attract costumers and actually working very well .

I presume that there is no point on placing a similar thread in the diyaudio to attract costumers but still articles comments and photos are nice to see and read for every one .

i would like to welcome any forum members if support schematic or any kind of help is needed and i will be more than happy to provide. Don't expect e mail in 2 minutes but i ll do my best to answer as fast is possible .

Most of those amps i keep schematics from, that i will be very happy to share and also i have very good memory resources about common failure and repair tips ...

enjoy
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SERVICE ΕΝΙΣΧΥΤΩΝ ΚΑΙ ΙΑΠΩΝΙΚΩΝ ΜΗΧΑΝΗΜΑΤΩΝ ΗΧΟΥ www.eastelectronics.gr
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Old 28th December 2011, 11:52 AM   #2
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Default SERVICE ADCOM GFA 545 ii

THE ADCOM GFA545

ADCOM at that time made simple circuits, simple construction, good design, plenty of streams and power supply , good quality material, extremely large capacity drive, sound upfront , the machines will put the theme literally in the face and no one will find coloring or smoothing the edges ...

In the above totals must be someone to add workmanship which compared to the price I would say that was good.

a think that i found wrong was ... the installation of the board upright resulting in accumulation of dust which is easily turned in maca which if we add a little moisture on prescription the boom is ready .... beyond the repair ( drivers and outputs+ capacitors ) a piece of duct tape between the cooling plate and he board will prevent future problems ...

from the very simple amplifiers which I like very much

fotos and schematic available
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SERVICE ΕΝΙΣΧΥΤΩΝ ΚΑΙ ΙΑΠΩΝΙΚΩΝ ΜΗΧΑΝΗΜΑΤΩΝ ΗΧΟΥ www.eastelectronics.gr

Last edited by east electronics; 28th December 2011 at 11:54 AM.
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Old 28th December 2011, 12:05 PM   #3
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Default SERVICE AKAI AM 2400

In the University of Athens we were told that we must declare Engineer and not just ... Electronics this has some basis and for me perhaps a little more because besides my father was mechanically engineer in the rectify surfaces, often skills needed beside electronic conversions to be able to do mechanical also .


The talk is about one AKAI AM 2400 in the hands of me these days, who has excellent mechanical construction but electronics inside was pretty messy and old

One key reason is that i liked very much the selector idea ... and the long piece of metal to keep signals in the back by far better than having them around the amplifier ...

for this unit .... complete recaping outputs and a general shape up ...

nice amp ... well designed .... after finished it i found the preamp to be not really good ...i had high expectations from this machine .... i have one of these on my own and may be in he feature i will make some upgrades

foto and schematic available
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SERVICE ΕΝΙΣΧΥΤΩΝ ΚΑΙ ΙΑΠΩΝΙΚΩΝ ΜΗΧΑΝΗΜΑΤΩΝ ΗΧΟΥ www.eastelectronics.gr
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Old 28th December 2011, 12:12 PM   #4
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Default SERVICE AKAI AM 6200

What to say anything ... rather ....

Terrible machine which is bad designed and if you look at it its just a cheap mess ...

was a series of AKAI that was nothing to talk about .
Despite these .. was the grandfather's ... so if anything is worth a little love (I am sure the grandfather was ready to give generously!)
A handful electrolytics .... 52 for the accuracy to make it work ... The result is that naturally came in good condition and probably a little better packed with terrible colorful sonics the distant past ... but ultimately this is the value of vintage ... enjoy some photo ...

schematic available
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SERVICE ΕΝΙΣΧΥΤΩΝ ΚΑΙ ΙΑΠΩΝΙΚΩΝ ΜΗΧΑΝΗΜΑΤΩΝ ΗΧΟΥ www.eastelectronics.gr
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Old 28th December 2011, 12:18 PM   #5
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Default SERVICE BETA 3 UA 600

professional Chinese AMP with history of problems resulting from poor design .....
Upright marginal electrolytics suffering from hypertension and temperature

the machine is honest and correct work in class G sound is is fine and the relation to the price is more than acceptable. Even once a manufacturing fault degrades an otherwise well-designed machine.

At very positive side is the proper construction and thermal cooling fans tri-modal robustness of construction and the power results

for a cheap amplifier beyond the capacitor error is an ok machine
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SERVICE ΕΝΙΣΧΥΤΩΝ ΚΑΙ ΙΑΠΩΝΙΚΩΝ ΜΗΧΑΝΗΜΑΤΩΝ ΗΧΟΥ www.eastelectronics.gr
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Old 28th December 2011, 12:31 PM   #6
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Default SERVICE DIY CRESENDO

Here is the crescendo 1982 140W who had been implemented by a colleague during those years full house kit along with protection and is powered by some GREEK company who made pcb but also seek parts for "kit" which was supposed to be some levels of quality .

Problems are well known that the designs of Giesberts had stability issues This machine worked quite well without too much oscillations and offset at the output.
of course this crescendo also features stabilization caps something i would never do in a machine of my own

What was not good was the implementation and the idea was to actually kill everything and start all over again from the beginning ... dismantled everything and did everything from scratch ... costly and difficult job, but at least finished was beautiful.

Apart from the photos I have a set of measuring of course if anyone has an appetite for debate on crescendo it could be very good to make it into a new post.

photo that was the machine before and after ...

Click the image to open in full size.

Click the image to open in full size.

Click the image to open in full size.

Click the image to open in full size.
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SERVICE ΕΝΙΣΧΥΤΩΝ ΚΑΙ ΙΑΠΩΝΙΚΩΝ ΜΗΧΑΝΗΜΑΤΩΝ ΗΧΟΥ www.eastelectronics.gr
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Old 28th December 2011, 12:33 PM   #7
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Default SERVICE DIY CRESCENDO ( after )

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Click the image to open in full size.

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Click the image to open in full size.
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SERVICE ΕΝΙΣΧΥΤΩΝ ΚΑΙ ΙΑΠΩΝΙΚΩΝ ΜΗΧΑΝΗΜΑΤΩΝ ΗΧΟΥ www.eastelectronics.gr
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Old 28th December 2011, 12:43 PM   #8
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Default SERVICE DENON PMA 520

The DENON PMA 520 as construction that i dont like very much

I do not like that has no auxiliary power supply ... It has only a stabilization for the amplifier and for the local stabilizers local transitors and locala capacitors that are rather small .....
This of course means that the currents circulating inside the machine is not clean ... and certainly do not make a quiet machine ...

In the minus will also put the electronic input selector who is known for quiet, friendly operation but the acoustic performance is the limited even for use in hifi.

Finally, the topology is the classic Japanese ... high voltage rails which provides much potential headroom but in the end 100% of power is not available cause of the limiters and transformer size that will kneel when 100% of power is requested and distortion figures will hit the sky ....


Generally an average machine ... found burnt resistors in one Chanel fuses soldering and a handful of electrolytics and a final good a good cleaning ...

fotos and schematic available
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SERVICE ΕΝΙΣΧΥΤΩΝ ΚΑΙ ΙΑΠΩΝΙΚΩΝ ΜΗΧΑΝΗΜΑΤΩΝ ΗΧΟΥ www.eastelectronics.gr
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Old 28th December 2011, 12:55 PM   #9
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Default SERVICE JBL MPX 300

In our company we do also professional amps ...don't know if there is some interest in presentations in this track, but let's see how it goes.


It was a very wise move by JBL to leave the design of the urei and create some machines that was probably based on topology CROWN-QSC ......

Smart machine, sturdy construction, proper cooling, carefully designed symmetric limiters, bridging, filter hpf to be able to work and without crossover, very good quality materials and construction, legendary output transistors 2SA1302-2SC3281 (the best bipolar transistor built ever from TOSHIBA)

in quality and power, true and honest machine and generally a very good professional amplifier .

The symmetrical limiters make very nice performance and power will be properly limited without distortions from the limiter it shelf push it hard. and that will mean no danger for the speakers ..

characteristics of a professional .... only disadvantage of the potentiometers were open but in reverse resulting mess and dust inside very easily .... Replaced with Alpha closed ... and go!

fotos and schematic available
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SERVICE ΕΝΙΣΧΥΤΩΝ ΚΑΙ ΙΑΠΩΝΙΚΩΝ ΜΗΧΑΝΗΜΑΤΩΝ ΗΧΟΥ www.eastelectronics.gr
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Old 28th December 2011, 01:14 PM   #10
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Default SERVICE AUDIO INNOVATIONS ALTO

AUDIO INNOVATIONS ALTO .....

The word INNOVATIONS in Greek will mean innovation, modernity or some cutting edge technology ... So the amplifier should be something innovative and new ..

Well actually its not talking on a project with a ziilion design flows , which comes from construction and implementation of how Dynaco did amps before 1970. sad isn't it ;;;

In principle, the amplifier is a blast from the past ... having a capacitor at the output just 2,200 mfd almost equal to a capacitor of a portable cassette player of the yera 1970 ... then the transistor output is the classic old dead slow 2N3055 and to complete the picture, the dc block capacitors at the input is just low enough resulting in a serious roll off from the 60 HZ and below ...

Somewhere here is the time at which the dealer has gotten a lawyer and are looking to fill me up lawsuits ... so maybe i have to rescue this ...


-------------------------------------------------- ------------------------

In practice things are not as sad as the description The amplifier is English substantial school itself is going on the prototypes and concept of the NAD 3020, and in general wants to say :

"" "We are Englishmen and we can prove to the world machines built from simple materials and smart design can create DECENT machines"

The truth is, that they actually DID IT ... although as the transistors are slow with "hard" work to do driving the load through the poor capacitors and at the input may have a roll off but generally for English rock sounds this is not a major problem and if the listener is not party animal things will go more than ok

replaced caps in the power supply with something better and something bigger (6 times up ) and of course the same and the output at 4700 mfd so it can support some more low end ...

bypass .... decoupling, cleaning .... one relay output and the machine is fine ... certainly has cleared a click above and beyond all the comments are a decent English construction ... .... good-looking machine with personality and identity, and because of its simple construction is extremely clean ...

found some resistors with poor soldering ... listen to it and after all i think i liked it .... same on me .... i consider my shelf a 2SA1302 guy

few pics from
Click the image to open in full size.



Click the image to open in full size.
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