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AU-719 on the bench

Hyperion said:
I searched around a lot, and discovered that Mouser had none in stock of anything suitable, so I had a look on Digikey and came up with these:-

https://www.digikey.co.uk/product-d...nics-cde/382LX123M080N062/338-2109-ND/2295339

12,000µF, 80V

With the space being limited to 40mm diameter, and needing to be 80V or more, there isn't much choice. (I really didn't want to mess about with 35mm diameter replacements).

BTW: I wouldn't have considered any EU suppliers, because of ridiculous import duty charges now being levied on a lot of goods to the UK by EU suppliers. So I only looked at Mouser, Hi-Fi Collective and Digikey.
Click to expand...

Sadly, EU companies are now required by UK law to be VAT registered and collect VAT for UK orders if they want to continue to sell into the UK. Many EU companies have pulled the pin on sales to the UK and all the forms etc to comply with our laws are just too much hassle.
 
sansui au719 said:
Sadly, EU companies are now required by UK law to be VAT registered and collect VAT for UK orders if they want to continue to sell into the UK. Many EU companies have pulled the pin on sales to the UK and all the forms etc to comply with our laws are just too much hassle.
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Here in the Netherlands we have that on orders from Digikey. Have to pay 28% on delivery. And they are the only one doing Sanken semiconductors. Luckely the cost of components aren't the greatest part of the costs for repairing/restoring the amplifiers
 
I have now replaced the Main Filter capacitors, listening to it now, it has lost none of its listening appeal as sometimes happens after changing such components.

Some statistics
Old filter capacitors "value, ESR, Ripple mV"
8748µF, 0.22, 100mV // 9510µF, 0.21, 90mV // 9842µF, 0.21, 75mV // 7982µF, 0.22, 60mV

New filter capacitors
10,950µF, 0.20, 60mV // 10,810, 0.20, 60mV // 10,760µF, 0.20, 50mV // 10,850, 0.20, 50mV

It sounds so much improved from how it used to sound, initially I thought it sounded pretty good for an unrestored ~40 year old, after this restore it now shows a more subtle side to its character.

Still 'To Do':-
I need to check the phono inputs, and I'll think about performing a power test and push it as much as I dare. ;) - then a final clean up, and check of all the settings when warmed up, and then this one will be done. ;)
 
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Here is the internal 'look' after the main filter capacitors have been changed.

IMG_3371a.jpg

Unfortunately the power output test was not very successful, as the transformer 'weakness' showed itself on the affected channel limiting output. But it's fine up to significantly above normal listening levels, which is how I understand Tony, its owner, has been using it up to now.

I haven't heard from Tony for a few days - so I hope he is all right, I know he has a few irons-in-the-fire gear wise, maybe that's keeping him busy.
 
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Hyperion said:
Here is the internal 'look' after the main filter capacitors have been changed.

View attachment 2131788

Unfortunately the power output test was not very successful, as the transformer 'weakness' showed itself on the affected channel limiting output. But it's fine up to significantly above normal listening levels, which is how I understand Tony, its owner, has been using it up to now.

I haven't heard from Tony for a few days - so I hope he is all right, I know he has a few irons-in-the-fire gear wise, maybe that's keeping him busy.
Click to expand...
I had a lead on a good transformer. 4 weeks ago was an AU 719 offered up with replacement toroidal transformers because one of the transformers died. I did an offer for with the original transformers but did not go high enough. I contacted the seller last week but he sold it to a German including both transformers. So that didn't work out.
 
GrisPato said:
I had a lead on a good transformer. 4 weeks ago was an AU 719 offered up with replacement toroidal transformers because one of the transformers died. I did an offer for with the original transformers but did not go high enough. I contacted the seller last week but he sold it to a German including both transformers. So that didn't work out.
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Thanks for looking. I know you own a 719, you're doing some Sansui restoring and you're active on the German markets (among others). I hope members like yourself can help us find a replacement. I found one listed for sale for £50 on a UK parts site but it had already sold. They may be rare but they are out there, so any help in finding one is very welcome.

EDITED : I also wondered if a compatible new or other replacement could be found (say from another type of amp). As long as it has sufficient current, is sufficiently shielded and has the right voltages on the secondary windings I don't see how a power transformer would affect the sonic character. Have I missed something ?
 
Hyperion said:
Here is the internal 'look' after the main filter capacitors have been changed.

View attachment 2131788

Unfortunately the power output test was not very successful, as the transformer 'weakness' showed itself on the affected channel limiting output. But it's fine up to significantly above normal listening levels, which is how I understand Tony, its owner, has been using it up to now.

I haven't heard from Tony for a few days - so I hope he is all right, I know he has a few irons-in-the-fire gear wise, maybe that's keeping him busy.
Click to expand...
Not much you can do with a bum transformer. It is what it is. Awesome work as usual. :thumbsup:
 
Hyperion said:
Here is the internal 'look' after the main filter capacitors have been changed.

View attachment 2131788

Unfortunately the power output test was not very successful, as the transformer 'weakness' showed itself on the affected channel limiting output. But it's fine up to significantly above normal listening levels, which is how I understand Tony, its owner, has been using it up to now.

I haven't heard from Tony for a few days - so I hope he is all right, I know he has a few irons-in-the-fire gear wise, maybe that's keeping him busy.
Click to expand...

I hope you got my email this morning John. I was very busy yesterday, working on a car. The insides look very tiday now. I'm happy it's playing beautifully. I'm sure we'll find a way to sort out the transformer issue.
 
GrisPato said:
I had a lead on a good transformer. 4 weeks ago was an AU 719 offered up with replacement toroidal transformers because one of the transformers died. I did an offer for with the original transformers but did not go high enough. I contacted the seller last week but he sold it to a German including both transformers. So that didn't work out.
Click to expand...

I wasn't thinking this morning. If the guy replaced a power transformer on a 719, what did he use for a replacement and, more importantly, where did he get it ?
 
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GrisPato said:
4 weeks ago was an AU 719 offered up with replacement toroidal transformers because one of the transformers died
Click to expand...
Arising from this little nugget, I've had a look around at Toroidal transformers - but the only ones I can find are too big! - there is 100mm of space between the left side and the PSU/Protection PCB (allowing just over 5mm clearance) to squeeze in two toroidals. But I am still in the dark about how much current capacity we need for the transformer secondary winding, I am thinking 4 or 5A. :idea:
 
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Hyperion said:
Arising from this little nugget, I've had a look around at Toroidal transformers - but the only ones I can find are too big! - there is 100mm of space between the left side and the PSU/Protection PCB (allowing just over 5mm clearance) to squeeze in two toroidals. But I am still in the dark about how much current capacity we need for the transformer secondary winding, I am thinking 4 or 5A. :idea:
Click to expand...
How much current do the rectifiers handle? Then go at least 20% - 25% above that to be safe.
 
Working backwards from the nameplate rating of 450W = 225W per transformer, neglecting losses and the current draw of the regulated PSU I'm only getting 1.78A secondary current (fused at 7A). Must be doing something wrong because 3.53A is needed to drive 8 ohm speakers at 100W.
 
Hyperion said:
Well that gives a figure of at least 4.2A, better 5A....

Thanks Skywatcher :thumbsup:
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Fuses (if any) on the secondary can be a clue too. If there is a 7A fuse, better go with at least a 10A transformer. That way the fuse blows before killing it.
EDIT: Surge current rating, not continuous rating.
 
DougBrewster said:
Working backwards from the nameplate rating of 450W = 225W per transformer, neglecting losses and the current draw of the regulated PSU I'm only getting 1.78A secondary current (fused at 7A). Must be doing something wrong because 3.53A is needed to drive 8 ohm speakers at 100W.
Click to expand...
Ahh yes, the surge current rating of the secondary comes into play too. A momentary surge from a short will blow the fuse before any windings get too hot to melt down.
 
I'm hoping GrisPato will come back with contact information for the guy who supposedly replaced the power transformers with toroidals in his 719. If that guy found just the thing it may save time.

Thinking about space, it would look much neater but is replacing both with toroidals strictly necessary, as long as both have the same specification ? Would mismatched types of transformers present a problem. ?
 
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