Sansui Au919 Parts
- Thread starter nikomi021
- Start date
xoaphexox
Supernatural Anesthetist
Have the amp all hooked up and playing The Lamb Lies Down on Broadway and it sounds fabulous!
I ended up rebuilding the power supply board and doing several other things I had not intended to do but heck once this amp is open in front of you it's best to do it all so you don't have to later.
I ended up rebuilding the power supply board and doing several other things I had not intended to do but heck once this amp is open in front of you it's best to do it all so you don't have to later.
noveltone
Active Member
Xoaphexox,
Congratulations on a finished re-refurb! You must feel pretty confident in the status of your AU-919 for the long term. What was the issue with the PS voltage? When you said you rebuilt the power supply, did you replace all the components?
Anyway, I'm glad it sounds great, as it should. Does it sound different than before, given the cap changes?
Collin
Congratulations on a finished re-refurb! You must feel pretty confident in the status of your AU-919 for the long term. What was the issue with the PS voltage? When you said you rebuilt the power supply, did you replace all the components?
Anyway, I'm glad it sounds great, as it should. Does it sound different than before, given the cap changes?
Collin
xoaphexox
Supernatural Anesthetist
The power supply issue was my mistake - I had created a solder bridge between two resistors that should not have been connected. No harm done, just removed the bridge and all was well.
I rebuilt the power supply because of the amount of corrosive glue slathered on the components. Replaced every electrolytic capacitor, the four transistors, and every 10, 15k, and 56k ohm resistor. I was able to leave the rectifiers, diodes, and film caps alone as they were either not near the glue or did not have enough on them to start corroding.
I definitely think it sounds better now - the bias and offset are stable - I replaced 8 trimpots with new Bournes units so I am sure that helped. I used to have a weird intermittent distortion and that is gone now as well.
I really think the unit sounds great and I took it upstairs to the bedroom where I will use it daily with the SE-7 and TU-919 as a headphone amp to put me to sleep and to drive two Dynaco A-25's while showering and getting ready in the morning!
xoaphexox
Supernatural Anesthetist
It's been about 2 years now and the AU-919 is still working great, however I am putting it on the bench again to replace the transistors in the flat amp after being inspired by a recent eBay auction by a fellow AKer.
The A992 and C1845 are simple to find. As for the C2071, still googling.
The A992 and C1845 are simple to find. As for the C2071, still googling.
xoaphexox
Supernatural Anesthetist
Scott, you mention to be careful of orientation. Is there something I'm missing? The 2SA1381FSTU and 2SC3503FSTU are ECB, like the originals.
Just want to make sure I'm not looking at this the wrong way.
http://www.fairchildsemi.com/ds/2S/2SA1381.pdf
http://www.fairchildsemi.com/ds/2S/2SC3503.pdf
Have a great holiday weekend,
Rob
Just want to make sure I'm not looking at this the wrong way.
http://www.fairchildsemi.com/ds/2S/2SA1381.pdf
http://www.fairchildsemi.com/ds/2S/2SC3503.pdf
Have a great holiday weekend,
Rob
xoaphexox
Supernatural Anesthetist
TR01 and TR03 on the preamp power supply?
It looks like the collector lead is snipped off and the screw is used to connect the collector to the circuit on the copper side of the board. How did you handle this with the different transistor package?
For the F-2845 power supply transistors I used OnSemi 2N4920G and 2N4923G. These were recommended to me a while back by one of the AK gurus, forget whom. Looking over the data sheets, they are much slower than the originals (3MHz vs 70MHz). Do you think that is an issue?
http://www.onsemi.com/pub_link/Collateral/2N491-D.PDF
http://www.onsemi.com/pub_link/Collateral/2N4921-D.PDF
scottrt
Well-Known Member
I used them on the main power supply board F-2845
hmm, the onsemi seem just adequate voltage wise, and I see what you mean about the low bandwidth.
I can't answer your question about their suitability issues, if any, as it pertains to these 919 power supplies. Hopefully one of the Gurus will chime in with some wisdom on this.
Scott T.
hmm, the onsemi seem just adequate voltage wise, and I see what you mean about the low bandwidth.
I can't answer your question about their suitability issues, if any, as it pertains to these 919 power supplies. Hopefully one of the Gurus will chime in with some wisdom on this.
Scott T.
xoaphexox
Supernatural Anesthetist
Just finished replacing all the transistors on the driver board. Dialed in offset to 0mV with no sweat. I noticed it was getting hot - the bias in both channels was 110mV! Must be from the new transistors... I was able to dial it down to 20mV and now things are all set.
I plan to refurb the connected/separated switch and the protection board next and then she's all set to get the oval caps rebuilt.
Good times!
I plan to refurb the connected/separated switch and the protection board next and then she's all set to get the oval caps rebuilt.
Good times!
Last edited:
xoaphexox
Supernatural Anesthetist
Added new diodes and zeners to the rectifier and protection boards. Also replaced the reed relay on the connected/separated board and disassembled the switch for a thorough cleaning. Playing right now through Minimus 7's on the bench and sounds great!
I think I am ready to send out the oval caps now, will be in touch via email!
FWIW, this is the reed relay I used: http://search.digikey.com/scripts/DkSearch/dksus.dll?lang=en&site=US&keywords=Z649-ND
The DC offset is still hovering around 0mV, so that's good, but both bias readings are hovering around 10mV after adding all the new diodes. Not sure why, will adjust them back up to 20mV after a few minutes of playing.
I think I am ready to send out the oval caps now, will be in touch via email!
FWIW, this is the reed relay I used: http://search.digikey.com/scripts/DkSearch/dksus.dll?lang=en&site=US&keywords=Z649-ND
The DC offset is still hovering around 0mV, so that's good, but both bias readings are hovering around 10mV after adding all the new diodes. Not sure why, will adjust them back up to 20mV after a few minutes of playing.
xoaphexox
Supernatural Anesthetist
Now that I've had time to think about this, I believe the difference in bias before/after was due to changing out the MV-103 triple junction diodes with strings of three 1N4148 in series. This was to approximate the 1.5V voltage drop. These four diodes were on the driver boards. They were the "epoxy ball" looking ones, not the "brown boat"s.
The unit sounds great and I think this preventative maintenance will make 2011 a year of trouble free listening!
The unit sounds great and I think this preventative maintenance will make 2011 a year of trouble free listening!
tututpouet
Member
What power transistors are used in the AU-919 ?
xoaphexox
Supernatural Anesthetist
xoaphexox
Supernatural Anesthetist
Nah, I had adjusted the bias to 20mV per the service manual and then noticed it was 10mV after doing more work. I then realized that I did change these triple junction diodes on the driver board, which must have been why.
The bias is now solid at 20mV after a small adjustment. The DC offset is also solid around 0mV.
