Akai aa6600 repair / refurb 2025
This receiver will be for sale at a later date, when all things are done, checked, a reasonable price is established and it being used for a few months.
Gemakshalve is deze pagina verder in het Engels geschreven.
This page is written using English language only.
I bought this Akai as a defective piece, it was sold as needing attention/fixup.
Initial testing showed one channel hardly present (95% soft crackling), the other channel did not sound good, either, but it was still present. It looked, the situation was caused by the preamplifier. The FM radio part was still capable of receiving, which was promising.
Partly, the black paint of the knobs faded, underneath is the gold/brownish color of the front "rings". This is irreversible so I regard it as "patina" ;-)
As always, the aim of this page is to share useful repair information and assumes technical electronics knowledge.
This very sturdy old receiver now sounds good again!
A look at the not-yet-refurbished receiver.
It still looks pretty good, but part of the text legens on the front are gone. At the back, it looks there is a new DIN socket for tape, there are Jack loudspeaker outputs (still to be tested) and one set of screw terminals.
Opening it up, a major eyecatcher is the transformer steering of the current output stages of the amplifier, something you will only see at late sixties/start of seventies era of solid state receivers.
There is some discoloration due to heat. The device looks roomy enough to be able to proceed in steps instead of totally take it apart.
Visible is a repair of the small input pair of transistors in one of the main amplifiers (European BC237 were used), so a main amplifier was once repaired (this apart from the new DIN socket for tape R/W.
On the picture on the right, it can be seen a lot of the lavender Matsushita capacitors were used.
Unfortunately, I forgot to make overview pictures of the old situation.
According things encountered, this receiver had repairs before, maybe more than once.
The Akai aa6600 power supply card 8005-1
An eyecatcher is the TIP33C transistor in the power supply. This is not the original one, so another repair. Probably it ever failed and it was repaired by somebody wanting to make sure it would never fail again and a high power one was chosen ;-)
Another interesting observation is the the circuit cards themselves were produced by Matsushita, according the logo on them.
To remove a little power from the (getting hot) transistor, I changed the 10 OHms R801 to 18 Ohms.
The power rectifiers were upgraded to 1N5408, the ones for the preamp to BYV96E. The Zener diode, also supplying the 12 Volts for the tuner circuits is a 1N4742A, now.
The electrolytic capacitors on the boards were all changed to Panasonic FC 470 uF. They are 105 degrees celcius types.
The R806 (on the picture but wrong in the schematic!) 330 Ohms power resistor was removed (still visible below on the picture) and replaced by 680 Ohms low wattage, is it is for the stereo indicator, which was replaced by a LED and trimming resistor on the stereo decoder.
The TIP33 power transistor/cooling piece was elecated by putting a washer underneath, getting rid of more heating up of the circuit card.
The last picture shows a 4700 Microfarad capacitor feeding the circuit card, and 10000 Microfarad 80V ones feeding the main amplifiers. The selection of the 10000 Microfarad ones was based on buying 10 each of this diameter for more projects, as using a 80V type may be regarded as "unneeded overkill".
The power amplifier boards
There is no bias current adjustment on the power amplifier boards. I decided to leave the output stages, if behaving correctly. I am pretty sure, the output transistors had to be carefully selected for behaving the same, therefore I did not attempt to exchange them. Also the 750 Ohms resistors which did change color to the heat I left in, because I have no suitable replacements in house.
Partly, the components at the input side of the main amplifiers are replaced.
The input pairs of transistors were replaced by BC547b, the input capacitors, electrolytic capacitors and the 100 Ohms discolored resistor. One was replaced by a brown one in the past.
The transistor on the cooling piece should be a 2SC931 according the schematic, but I found a TIP41C on both amp channels. Probably, it was replaced, in the past.
The tone amplifier board, called 9004
The tone amplifier had the old Hitachi transistors, as can be seen from their looks. Interesting too is the metal transistor on the most right picture almost on the most right hand side, this was a BC129B, a sign it was replaced many years ago when this part was around. apparently one of the 2SC458 transistors already failed in the old past.
All parts were replaced, apart from the potentiometers. Fortunately, they were still good.
IIRC, I used BC549 for all audio small signal transistor replacements.
R911=6k8 (not clearly visible in the schematic. C906A/C907A have a wrong designation on the circuit card, the caps look interchanged but are on the right physical spot.
The EQU/AUX amplifier board, called F9005
Also here the always suspect 2SC458 transistors. During test before demolishing, one second transistor appeared having 8 Volts, the other 12, so at least (also) here was something wrong.
All parts were replaced. Resistors all high quality low noise metal film, of course.
The Tuner boards.
The actual FM tuner front-end is a 3-gang sealed one, I left it alone, btw:there are no electrolytic capacitors inside.
The tuner related IF / AM /stereo decoding circuit cards did get their aluminium electrolytic capacitors replaced.
The stereo lamp was replaced by a high brightness LED. I mounted a trimmer potentiometer onto two current limiting resistors, it is the white little trimmer. Experience made me bypass the LED by a resistor, to make sure it keeps totally off when it should be off.
This will also make sure the power supply transistor will generate less heat, as it does not have to supply some 40 milliamps to the lamp, at the moment. This transistor together with its series resistor would dissipate some 400 milliwatts extra during stereo.
The receiver backlighting.
The scale backlighting was, as expected, in a bad shape.
The metering backlights were one blown lamp and a LED one which gave some strange effect. Those lamps were switched depending on tuner selection (the left one) and FM selection (the meter on the right)
Below, find the new situation. I used a RGB strip. The meters did get a piece of strip powering the green part of the LED's only.
The scale lamps frame did get the blue and green led connected, so I needed a total of three current sources to steer the LED's for intensity.
The intensity of the lighting can now be adjusted, and for the scale the greenish blue can be color adjusted, also.
The schematic of the light steering stripboard and lightstrings.
The 6.5 Volts AC from the lighting output gets both a plus and a minus single rectifier, to be able to get some 15 Volts DC total when rectified.
Experimentation showed some 10 Volts was more than enough to get an already very high brightness from the LED's. Therefore, the LED strings get a little less than 11 Volts maximum voltage, as defined by a Zener diode.
There are 3 channels, having detachable wiring to the LED strings, two for green and one for blue, each having its own trimming potentiometer for brightness.
The front of the receiver.
Side 1. I still have to polish the transformer top....
The Back.
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