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Sansui AU-999 DC problems?

Sp33ls said:
Got it! Yeah, I'll leave it in for now. After several raving reviews, I'm picking up a pair of Buchardt S400s (which are more expensive than the Sansui).
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The trick to the crowbar DC protection circuit is to make sure it has the correct fuses in it, they must be quick acting fuses.
 
Sp33ls said:
Do you miss it? I'm guessing you might find more satisfaction in knowing that a friend is getting good use out of it.
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I have other gear which exceeds the performance of the AU999 so not really, but when one comes in for me to repair or restore, I sure enjoy listening to them when I run them in....
 
Thank you everybody for being so welcoming! I also learned a lot from my dad (HI HI as he put it).

So do you leave em in there untested? How do you know the speakers even are protected from DC? I mean you can check the diodes and transistors on there with a MM but that isn't 100%. Someone better at network analysis than me should design a little protection board we could plop in there that had a relay and ran off the pre amp voltage or something. Then we could run the outputs through the protection, rather than in parallel with them.

These amps also have speaker fuses and rail voltage fuses. It is not like you're leaving the speakers completely unprotected. Although the 5A on the speakers might be a bit much (they do have to deal with DC voltage at start up, no relay, doh). Still, they would go if full rail voltage ended up on an output.
 
Trnsfmr_Jr said:
Thank you everybody for being so welcoming! I also learned a lot from my dad (HI HI as he put it).

So do you leave em in there untested? How do you know the speakers even are protected from DC? I mean you can check the diodes and transistors on there with a MM but that isn't 100%. Someone better at network analysis than me should design a little protection board we could plop in there that had a relay and ran off the pre amp voltage or something. Then we could run the outputs through the protection, rather than in parallel with them.

These amps also have speaker fuses and rail voltage fuses. It is not like you're leaving the speakers completely unprotected. Although the 5A on the speakers might be a bit much (they do have to deal with DC voltage at start up, no relay, doh). Still, they would go if full rail voltage ended up on an output.
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You can test them, you can turn the SCR on with an external DC voltage.
I don't really understand why people get so wound up about the crowbar circuit, it was one method of disconnecting the speakers from the amp with the presence of DC on the amplifier output, they are in many many amplifiers of that era......
Next time I have a AU999 in I will do a thread about the crowbar circuit, and go through it and demonstrate it.
 
Haha, I think it just takes one amp committing suicide and then you start to really hate them! Don't mean to sound wound up, just enjoying talking shop. I'd enjoy your write up. That's kinda what I was saying. Only way to test them is by hooking up an adjustable PSU. I guess a 9v might work, I have never thought of that before though. (haha if the battery gets hot, it works!)
 
Trnsfmr_Jr said:
Haha, I think it just takes one amp committing suicide and then you start to really hate them! Don't mean to sound wound up, just enjoying talking shop. I'd enjoy your write up. That's kinda what I was saying. Only way to test them is by hooking up an adjustable PSU. I guess a 9v might work, I have never thought of that before though. (haha if the battery gets hot, it works!)
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Oh no, I know you're not wound up, there was a heated discussion about it a while ago.
Current limited bench supply is what I use.
I think it might be a good thread to do so there is a better understanding of them.
 
We all agree that the 999 is an amazing amplifier that can run with some of the bigger more expensive boys :thumbsup:

On the rectifier subject I am thinking preventive maintenance and forward reliability since those diodes already have close to 50 years on them at less inrush current that what you are giving them for its post resto lifespan.

To really know if these rectifiers can be a weak link across the remaining stockpile, you'd need a much larger sample than 5-6 - not dismissing that those you do take through the wringer have proved to be strong for that particular unit, but not everyone test them like that.
 
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stereofun said:
We all agree that the 999 is an amazing amplifier that can run with some of the bigger more expensive boys :thumbsup:

On the rectifier subject I am thinking preventive maintenance and forward reliability since those diodes already have close to 50 years on them at less inrush current that what you are giving them for its post resto lifespan.

To really know if these rectifiers can be a weak link across the remaining stockpile, you'd need a much larger sample than 5-6 - not dismissing that those you do take through the wringer have proved to be strong for that particular unit, but not everyone test them like that.
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Well there you go.....its all good, I'll let you know when I find a dodgy one......Where does it stop? The resistors are 50 years old? We should now replace all the resistors.....See where I am going?
Although, its only going to take one of the rec's to fail on one of my restos, and they'll then go on the mandatory replacement list....
 
stereofun said:
We all agree that the 999 is an amazing amplifier that can run with some of the bigger more expensive boys :thumbsup:

On the rectifier subject I am thinking preventive maintenance and forward reliability since those diodes already have close to 50 years on them at less inrush current that what you are giving them for its post resto lifespan.

To really know if these rectifiers can be a weak link across the remaining stockpile, you'd need a much larger sample than 5-6 - not dismissing that those you do take through the wringer have proved to be strong for that particular unit, but not everyone test them like that.
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It is a 3A rectifier with a 4A fuse on the main AC line. Given that the voltage outta the transformer is something close to half of the voltage at the AC input and therefore something close to twice the current of the AC input (not including the other taps and assuming 100% efficiency- napkin math here) there is no situation where the rectifier wouldn't go before the main fuse. I think it is best to have fuses go before essential components. Also, as you say, we all upgrade the filter caps compounding this problem even more by increasing the in rush.
 
My sample consist of two... 50% failing rate :p.
kevzep said:
The resistors are 50 years old? We should now replace all the resistors
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Hell yeah!! Specially on the that 9001 that you have there :bigok:.

Is great to see Trnsfmr_Jr hanging around!! Welcome :beerchug:
 
Kev, I get your point with all parts being 50 years...where do you stop ? - so all we can do under the constraints of budget, time or ambition is to replace what we believe are valid bets :beerchug:
 
stereofun said:
Kev, I get your point with all parts being 50 years...where do you stop ? - so all we can do under the constraints of budget, time or ambition is to replace what we believe are valid bets :beerchug:
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Thats right, and you know, we are all very passionate about our Sansui's, its great!!

Where else can you go to get so much information about many models of Sansui........this is the place....
 
Another tidbit of advice: Avoid using the AUX input for your best source - here the signal first goes through a small diameter input-level pot, then a shared rotary switch. I prefer Tuner, because it is straight in and has its own dedicated switch lever. At least, when using Aux, give the pot in the back a good de-ox clean and work out, these rarely move and has likely never been cleaned.
 
stereofun said:
Another tidbit of advice: Avoid using the AUX input for your best source - here the signal first goes through a small diameter input-level pot, then a shared rotary switch. I prefer Tuner, because it is straight in and has its own dedicated switch lever. At least, when using Aux, give the pot in the back a good de-ox clean and work out, these rarely move and has likely never been cleaned.
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Yes those trimmers on the back do always need cleaning. I can't say I have never heard a degradation in Sound quality using the AUX input, I like it so I can trim the input level to match other inputs....
 
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