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I watched your video... I wanted to point out something that i see you overlooked.... You were perplexed about the bias problem and focused on that thermistor and what to do about it.. what you overlooked was the fact that there is an adjustable two lead 500 ohm potentiometers Vr03,04 that is in line (parallel) with that thermistor which is in essence your bias adjustment pot which ranges from zero to 500 ohms.. The thermistor is there to only create small offsets of resistance as the unit heats and cools to compensate the changes in semiconductor characteristics as there is thermal changes. The thermistor is not used as the primary resistance factor for bias, just supplementary and will not properly compensate if the potentiometer is set too high in resistance or is open. The bias circuit comprises of the two diodes De01, 02 and De 03, and 04, the 500 ohm potentiometer and the thermistor in parallel with it. Your issue is that the bias pot was likely very dirty or bad. When you jumped out the thermistor you were in essence turning the bias to one end...zero ohms. The "fix" you did was in essence you bypassed both the bias pot and the thermistor and created a very low fixed bias adjustment that wont be able to offset when the unit heats and cools. With the bias fixed so low ,you will likely have a higher spec notch distortion by doing so but on a low end unit like this, i am sure it will likely not be very noticeable LOL. If you still have this unit.. replace the bias pots and then you can do the adjustment to where the bias should be and also remember to keep/put back in that thermistor in line as it was..... There is another adjustment pot which is your quasi complimentary balance adjustment pot VR06. Visually it is adjusted so there is even cut off at the tops and bottom waveform point of clipping or lowest point of distortion or it can be adjusted where it there is half positive VCC between the two output halves.. ( for example. if say QE12 collector is 46V, QE10 should be 23V )

I would be a little nervous with a relatively heavy receiver or amplifier on a fairly flimsy plastic table, especially outside on a raised deck like that. Just having the screws roll around on the bare tabletop (instead of putting them in some container) seems like a bad idea too. The white tabletop and natural light does let you get some good thumbnail shots, but doing any serious or precise work out on the deck wouldn't be my first choice.

It's nerve wracking seeing the loose hardware on that folding table! I use an old ice cube tray to keep hardware organized, and write a brief description of each cell's contents on a clipboard as I go.

Most honest, genuine, to the point, video. THank you.

Definitely gonna be a fun one

Montana looks beautiful. Hi from Alberta.

Love sansui equipment... pretty well made.. great video as well. Thank you. ✌️❤️😁

I have Pioneer C73 preamp. Unlike your amp, I have some static from my volume control knob, and it seems like its sealed as well. How would you recommend cleaning that? Thank you.

Nice to see back again brother! I absolutely love the looks of that year Sansui Receivers. The first one I bought was a 7070 & then the addiction grew & went on up the ladder until I reached the 9090db which I've own 3 of. It's been fully restored & absolutely fabulous sounding.

That was simply blessed labor! That Mac 1500 sounded simply fantastic! Thank you SO much posting this most important iconic receiver!🌹

I simply adore terrestrial FM Stereo sound. You’ve done remarkable work. Please keep going.🌹

I like the 8080, better than the top dog 9090. It’s got a much more conservative appeal. And it’s 94W/ Ch are still very potent! A beautiful presentation.

Crows are vindictive, Aiden...If you piss them off, they will retaliate! Lol

True story.....I picked up a beautiful 7070 from a thrift for $20 about 5 years ago thinking it was a Realistic model. Threw it in my cart and when I got home I took a closer look and realized it was actually a Sansui! What was even more of a surprise was that it worked perfectly!

Kudos for quickly finding the issue with this receiver. I commend your direction on this problem and getting it fixed with efficiency. There is something to be said with practical experience and find we are always learning as we go. With that said, for your reference Q5 and Q6 (the 2sc1318 transistors you replaced to solve the issue ) are not bias transistors.. This amp topology is a full complimentary push pull design using direct coupled stages and has no output coupling (OCL) whatsoever hence why it has a differential stage with dc stabilizing feedback. Each channel uses a single ended simple Pre-drive class A gain/constant current source device direct coupled from the differential stage to the driver stage which are the transistors you found faulty. The variable resistor and stacked diode (thermally coupled to the heatsink) array is your bias circuit as well as the path for the positive signal and current source. The transistor you replaced is in turn not a bias transistor at all. These lower power units did not incorporate any transistors in the bias circuit. Also Bias failures do not lead to high DC voltage as much as it would lead to over current situation of the output devices being turned on too long between the complimentary pairs. What was likely happening is that these matsushita transistors were intermittently breaking down and you were losing your pre-drive/constant current source and since this device directly coupled at this point to the PNP drive, the circuit went into saturation on the negative drive side and was just pumping a large negative voltage as a result. ( note in your video it was -14VDC)

Pyramid audio has a far easier discreet solution that fits directly in place of the STK0050 packs with no assembly and is extremely stable. Its only two semiconductor devices ( dual darlington devices with a few SMD devices soldered to the board.. easy peasy.. I have used them before with excellent results!

Thanks!

What a great view from the deck! Good to see the "supervisors" in the video again. Beautiful receiver. Thanks for putting another informative fix it video together. Always look forward to new ones.

I loved this video because I have a Sansui 5050. My son found it on Craig's List for 75 dollars and it is in perfect, mint condition. I feel bad that you had to do so much to clean the pots because the 5050 took me no time at all. I took the cover off and there they were. I can vouch for the FM sensitivity too. I also have two feline co workers but only one ever gets involved with my repairs. LOL

Earned a sub with that one. Nicely done.

Thanks

I think the reason to stick capacitor with the relay is to reduce vibrations. As I can see, the capacitor is a few millimeters above the board.

I have a 8080 and just had it serviced half a year ago, runs very well but recently my aux switch went out. Probably go and get it serviced again. I also use a Sansui 2000X. Peace & love

I had a model 7070 and worked for 40 years

nice video,. great view,. im gettin Shango vibes with the electronics outside,. i love ur kitties name,.lol

So have you dropped anything off the table and down through the deck to never find it again? 😮

I agree regarding the speaker terminals. What a cracking job. Well done.

Yes the pot

Or the volume pot is a little off

😸👍

Long time viewer. I'd really like a video on the equipment and hookup you use for testing. Signal generator, Osc, etc. Thanks!!

Oh snap! LOL

Beautiful out there! Nice place to work.

I am sure you have video where you show exactly where you spray the Deoxit on both types of switches? Wanted to make sure I do it right. Thanks in advance.

Great video Aidan👍👍 Yep, dirty switches and old capacitors are the two biggest problems with vintage stereo receivers it seems. Nice balcony scene, definitely have a view and having furry helpers doesn't hurt. Thanks for the video and work, always interesting and fun. Enjoy!

No Pad protecting Receiver from hard, abrasive table top?

Nice outdoor setting & lighting, but I'd be concerned about dropping small parts through the decking as they'd be gone forever! 🤔

I don't remember the details, but there's a really easy mod to have the tuner dial lights on all the time, which just requires moving a pin to a different slot in one of those plastic headers, no soldering required.

Great job! I have same receiver sitting for maybe 20 years. I loved the quality of it and you made me to think get it out of storage and check it. If you come across a power amp, that making cracking noise, please make a video.

I'm guessing no-one mentioned 'be careful after replacing the fuses after biasing on 8080/9090's as the filter caps won't discharge on power off' lol. There's a trick to it - solder two leads to either side of a blown fuse for each channel and use those in place of the fuse to do the bias, bias, then power off, remove the amp board and use a fuse puller/pusher to pop the fuses back in. That way, it removes the danger of shorting the amp board/outputs when popping the fuse back in. The 9090 was one of the amps that hooked me directly up to our national grid (240v), was a fun afternoon that one.

Hello SADE

love the outdoor class with the cool Professor

That receiver looks to have been well taken care of. I have a 9090db I recently restored and I think it sounds great. Thanks for the video

Hey, I've got this old amplifier that I love. It's a Realistic AM/FM tuner compact stereo. The controls need to be cleaned because they're all sketchy, and the volume distorts when I turn it up too high. The FM tuner feels really loose too, but I don't really use it that much. I used it as an outdoor radio for a year, and it worked great, except for the junky speakers I had it hooked up to.

You just got over 20 watts at 15Khz and you just ignore it? I think your Fluke is the problem, most multimeters don't go that high. Buy a modern oscilloscope that shows the correct value and problem solved. Greetings from the Netherlands.

Very nice job. What are those speakers you have again?

Wow, special effects and a diverse group of co workers to talk with. Nicely done Aidan, love the addition of the table to take advantage of your outdoor workshop extension.

ohhh, funy to see how you manipulate those screws in a gobly table and if you drop one, will go down the deck and above! So fearless!!!

Hello from Meaford Ontario Canada : The reason the lights go out when switching from tuner to Aux is because the lamps can give off an rf signal and bleed into the other channels and it is done this way for audiophile purposes

Had an issue on a 80s JVC that was going into protection due to oxidation on a switch causing a short.