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Simonon

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About Simonon

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    Adelaide
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    Australia
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    Simon

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  1. The 2 Gxc760d units in my posession both had new belts, motor bush lubed and speed adjusted to spec. One had an erratic Vu meter and intermittent channel which I traced to some troublesome Hitachi 2sc458 transistors in the playback circuit. Depending on the serial number your unit may have these transistors. Both of mine had numerous dry solder joints and I replaced the power supply capacitors. One unit is waiting for new pinch rollers as I have a tape skewing issue on it. These are proving difficult to procure from my supplier at present. They are great decks and sound fantastic. They use a discrete logic control so I suspect you have an electronic fault in this area. A competent tech will be able to fix. You may have the same supply issue as one of my units if it needs pinch rollers however.
  2. I have rebuilt 2 of these decks and they are built like tanks but difficult to work on. You really need an old school tech with experience on these. I found this guy on Gumtree under the audio category. His name is Jorge and he is located at Ringwood in Victoria. I would recommend him and his experience listed below. Maybe look up Gumtree and call him. Cassette deck repairs, restoration and service; offered by qualified and experienced "vintage Technician" My fully equipped electronics workshop is at my home in Ringwood North, you can trust the quality of my work! I also repair "vintage" audio equipment, like: Stereo Amplifier, Receiver, Turntable, Cassette deck, Reel to Reel tape recorder, Speaker, Audio mixer , Walkman cassette player, I truly am one of the few "vintage" audio electronics technician, who are not yet in Heaven! I completed Valve amps Stereo solid state Hifi and early TV course in 1972, then completed my education in electronics at Sydney Technical College in 1977. 1974 to 1985, I was trained by German and Japanese manufacturers of Hi-end Hi-Fi audio equipment and worked as an Audio Electronics tech for these distributors in Sydney and Melbourne including Goldring engineering, kenwood, and Klap Electronics in Mel. Aiwa, Akay, AWA, B & O, Blaupunkt, Denon, Dual, Garrard, Grundig, Harman Kardon, HMV, Kenwood, Kriesler, Luxman, Marantz, Nakamishi, Mormende, Onkyo, Phillips, Pioneer, Revox, Rotel, Saba, Sansui, Sanyo, Sharp, Sony, Teac, Technics, Telefunken, Thorn, Toshiba and Yamaha. Please contact me for Service, repairs or restoration work. The hourly rate is $95 per hour. Jorge the "vintage Technician" Regards Simon
  3. Here are some pictures of a 1964 Nagra 3 NP that I have just got going. A full track mono machine with solid state germanium transistors it sounds very nice. Very impressive build quality. Good for the next 50 years and they definately dont build gear like this anymore.
  4. I have restored some bad cases but that one is the worst I have seen. A good scrub with soapy water and rinse looks like the only answer. I would be careful soaking the mains transformer and remove it before soaking and look at an alternate way to clean it. The transformer windings will need to be checked for shorted turns and meggered for leakage to ground. After cleaning the unit I would place overnight in an oven at around 60 degrees to dry. Possum wee is highly corrosive and I would expect eaten copper tracks and component leads. Hopefully it has not penetrated the mains transformer or even the printed circuit boards. Good luck with that one.
  5. Such a simple little amp that took 5 times longer to fix than it should have. If it were more complex with expensive output transistors it could have been a disaster. It is advisable to check that no Dc is present at the speaker terminals of a vintage amp, the idle current is set correctly on both channels and Dc offset is correct. A telltale that something is not right is one channel running hotter than the other. My usual standards were not adhered to initially and if this was a dc coupled amp direct to the speakers the result may not have been pleasant. Luckily this amplifier is has a coupling capacitor on the speaker output.
  6. It would have come with the links originally and they must have been removed to add a processor or most commonly an equalizer by the previous owner. It is not a band aid problem as RCA leads are just longer links. Their is nothing wrong with your amp. Trust me you have nothing to lose
  7. so grab another rca lead and link together processor in to processor out on both channels
  8. Grab a spare rca cable and link both channels of processor in to out. Plug you cd player into cd on the amp. Make sure cd is selected and cd direct is off. It should work. This is a common trap with these amps
  9. Their should be little links in between. Grabbing an Rca lead to link together is a simple task. I bet it fixes the issue
  10. Put an rca cable in processor in and out. I think you will find the amp will be fine. They normally have some little links which have obviously been removed.
  11. Download the manual. I still think this will be the case if it only works on the cd direct. I say this because I fell for this once.
  12. Does it have a preamp in/ out rcas on the back. If so they should be linked.
  13. Yes I did measure the HFE of the one from the good channel and the fakes. They were vastly different so I would assume they were not of equivalent voltage and current rating hence the reason they failed. I then fitted original new old stock transistors to both channels and found setup to factory spec to be easy with little drift in idle current once the amp warmed up. I guess the lesson of this post is to be careful with your component sources and not blanket change everything for the sake of it. You could create more problems, reduce performance or suffer a catastrophic event that destroys your speakers.
  14. I decided to write this article after a somewhat frustrating time rebuilding a vintage early model Sudgen A48 mk2 amplifier that I acquired. It was purchased apparently working and one output stage had been recapped with a number of driver transistors replaced with the other channel working. I restored the rough looking case and left the electronics due to lack of time. I began to notice a small amount of distortion on the untouched channel and pulled the B+ supply fuse where the idle current is measured. The problem was obvious with factory spec idle current being 150 milliamps where this channel was at 10mA meaning the output transistors where effectively cutoff at low volume levels, hence the distortion. The so called rebuilt channel measured 350mA and was getting hot so there was also a problem here. This is a relatively simple push pull amplifier at 40 watts per channel and is biased into class A for about the first 5 watts, hence it is a class A/B amplifier. An attempt at setting bias current on the untouched channel yielded no adjustment with a poor DC balance offset, so whilst this channel worked to a fashion it was way out of spec. The rebuilt channel allowed me to correctly set bias current and DC offset so I thought why not rebuild the faulty channel to be the same as the good one. Simple I thought and just a matter of ordering the same equivalent transistors as the good channel. I measured all resistors and replaced the DC offst and bias current potentiometers with bournes multi turn types. I then replaced all the BC547/ 557 transistors and found one BD519 driver transistors to be leaky base emitter. I thought great thats the problem and I will just replace the BD519 with a 2SD600 which is obviously working in the good channel and is similar specs. Sooo I ordered six 2SD600 trasnistors from a well known supplier and fitted them. Guess what happened...... the bias current crept up to 2 amps and the transistor failed. I checked everything again and replaced the transistor and it failed again. I then swapped the 2sd600 from the other channel and it worked. My conclusion was the transistors ordered where counterfeit. Checking HFE showed this to be the case. It was at this point that I decided to rebuild both channels to factory specs as it was noticed that the quality of workmanship of the good channel was pretty terrible. I found some new old stock BD519 driver transistors on Ebay Germany and ordered some. All electolytic capacitors where replaced with quality axial types and out of tolerance resistors replaced. So what did I learn from this exercise always be suspect of previous work especially if non factory spec components have been used try your best to confirm that transistors and semiconductors are genuine and be aware that many on EBAY are counterfeit. Remember that many through hole component stocks are now obsolete and some 40 years old. The counterfeit market for components is huge. This could spell disaster if you are rebuilding an expensive vintage amplifier such as a Yamaha or Sony VFET. Your vintage amplifier may never perform the same if you fit counterfeit components. Blanket changing electrolytic capacitors is not the answer and you may change the sound of the amplifier for the worse. Make sure both sides of the amplifier are running at roughly the same temperature. If they are not it usually spells trouble. When both channels are running the same idle current and set to factory spec it is amazing how stereo imaging improves I have rebuilt many amplifiers and this simple one took more time than expected due to cutting corners from my usual standards. It now looks new and sounds great
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