907 imos .....Blown output mosfets ...need replacements advice

[Tom B]

Came and went so quickly?
Every large format Concert sound system using the latest technology are all using MOSFET power amps. Nobody uses Bipolar power amplifiers any more, only older systems....
We have retired all our BJT amplifiers.

So I guess I am just an old Dinosaur who will stick with the beautiful vintage units from the late 60's, 70's and early 80's.
I love collecting, repairing and restoring these older vintage units that use typical BJT devices
I just closed down my beach club for the season, and had to remove my "Sound System" from the Cabana
I use a recently restored Quad Pioneer (QX-747) so that I can easily set different volume levels for the pair of inside cabana speakers, vs the pair of Pioneer CS33a's that I use outside the cabana. Attaching a picture of the Pioneer Receiver, and notice the Akai GX head 8 Track unit on top that is a daily driver.


I used to install/service/support Business Sound systems, but that was a long time ago in the disco days, where sound was a lot more contained that at a modern "Concert". 2 or 4 big speakers like original EV Eliminators, being driven by a couple of Akai or Phase Linear Amps usually covered the place very nicely. Maybe if I was still active in the sound system business as I was in the 70's I would be using big Mosfet amps. But seeing that I am retired from my career running Big Bank Data Centers, and being 67 years old, I should stick to my enjoyable work with vintage gear. And besides, I probably couldn't move those heavy Mosfet amps around anyway.

 

[kevzep]

So I guess I am just an old Dinosaur who will stick with the beautiful vintage units from the late 60's, 70's and early 80's.
I love collecting, repairing and restoring these older vintage units that use typical BJT devices

Absolutely, and so will I, as I sit here working on a Dinosaur SX1250, which I love, no other time and place appeals more to me that the 60's, 70's and early 80s...
Heavy? Nah MOSFET class D amps we use are light, the ones we use are 4ch of 3,300watts RMS in a 2U rack space, can drive 2Ω if need be and they weigh 32lbs each.
Class AB MOSFET are heavy, but nobody uses class AB any more either, its all this new fangled Class D Hoo Haa with onboard DSP for the speaker system processing....

I hear ya...I've got a few years to retirement, but I'll be glad to be out of this business when all is said and done...

 

[Shavalievdd1]

check this, there are couple photos of transistor http://amp8.com/sansui/a907/au-a9072.htm

 

[quadklipsh]

I am eyeing the amp8 repair site . But this one could be a different amp. Its a an alpha 907 ....not the alpha 907 imos limited and the transistors are also totally different numbers ....

 

[kevzep]

Take a picture of the device for us please, I think its a TO-3P type package, if it is, there will be a modern equivalent, I bet I can find one...

 

[skippy124]

I am eyeing the amp8 repair site . But this one could be a different amp. Its a an alpha 907 ....not the alpha 907 imos limited and the transistors are also totally different numbers ....

That is correct the amp8 link is for the 907 - it uses BJT transistors, the 907i useds the mosfets.

 

[restorer-john]

Take a picture of the device for us please, I think its a TO-3P type package, if it is, there will be a modern equivalent, I bet I can find one...

There is no 'modern equivalent'. They are a) available in numbers ex-Japan and b) not an easily substituted device in any case.

They were used in vast numbers by many makers in their TOTL integrated Mosfet amplifiers in the late 1980s/early 1990s. (Marantz/Luxman/Accuphase/Sansui/Sony/etc).

They are not hard to get, my supplier in Japan currently has 150+ in stock of grade Y of each type.

They are of course a T03P case. some pics of the devices in this thread when I did a PM-95 recently, post #56:

http://audiokarma.org/forums/index....ognize-it-and-have-any-info-pic.754558/page-3

 

[kevzep]

There is no 'modern equivalent'. They are a) available in numbers ex-Japan and b) not an easily substituted device in any case.

They were used in vast numbers by many makers in their TOTL integrated Mosfet amplifiers in the late 1980s/early 1990s. (Marantz/Luxman/Accuphase/Sansui/Sony/etc).

They are not hard to get, my supplier in Japan currently has 150+ in stock of grade Y of each type.

They are of course a T03P case. some pics of the devices in this thread when I did a PM-95 recently, post #56:

http://audiokarma.org/forums/index....ognize-it-and-have-any-info-pic.754558/page-3

I am just thinking outside the box.......They will not be around forever......

 

[restorer-john]

...They will not be around forever......

True enough.

These TOTL integrateds however deserve the original parts where we can get them. Many of them were hand-matched too, and used the top grades, which makes it an expensive exercise to rebuild them. One has to buy bags of 50 minimum to match two sets of 4 for each type.

Consider that PM-95 I rebuilt was AU$5999 in 1991 and that Sansui in this thread would have been well over $3k and it's worth it IMO. I'm down to my last 20 or so of the J115/K405s and am going to get another 30 of each in a month or two- it may be the last time I can buy them- who knows.

 

[kevzep]

True enough.

These TOTL integrateds however deserve the original parts where we can get them. Many of them were hand-matched too, and used the top grades, which makes it an expensive exercise to rebuild them. One has to buy bags of 50 minimum to match two sets of 4 for each type.

Consider that PM-95 I rebuilt was AU$5999 in 1991 and that Sansui in this thread would have been well over $3k and it's worth it IMO. I'm down to my last 20 or so of the J115/K405s and am going to get another 30 of each in a month or two- it may be the last time I can buy them- who knows.

Yes I agree and very good point, I lean towards working on solutions which are readily available because NZ is so isolated, but sometimes that is also a losing battle too....
I working on some of our Class D power amps which are only 7 or 8 years old, I went to order some Gate Drives, do you think they still make then? Of course not, obsolete after 8 years!!

 

[quadklipsh]

restorer john ....
what are the prices of your stocks

 

[Shavalievdd1]

http://amp8.com/sansui/a907/a907imow.htm

here he used non-OEM transistors, as they bigger than originals.

 

[quadklipsh]

he has shown three transistors
J-200 is readable and is larger than the 2SJ-115 (original) .
Is this good or bad ????
why did he not go for the EXICONS???
Do the newer replacements enhance power output of the amp too ????

 

[quadklipsh]

 

[kevzep]

he has shown three transistors
J-200 is readable and is larger than the 2SJ-115 (original) .
Is this good or bad ????
why did he not go for the EXICONS???
Do the newer replacements enhance power output of the amp too ????

No, the power output is determined by the rail voltage.

I would like to know what that TO247 Mosfet is though, it will have better dissipation than the originals...that is a good thing. It may well be higher current too...

 

[petehall347]

2sj200 seems to have high specs .. just compared to 2sk1058 .. which is in the larger package ..

 

[Shavalievdd1]

No, the power output is determined by the rail voltage.

I would like to know what that TO247 Mosfet is though, it will have better dissipation than the originals...that is a good thing. It may well be higher current too...

i think this guy from Japan don't want to share his experience that's why all label on new transistor are hidden.

 

[restorer-john]

i think this guy from Japan don't want to share his experience that's why all label on new transistor are hidden.

Fair enough too. Likely it has taken him decades to learn his craft, and source components others cannot. It is his business after all.

restorer john ....
what are the prices of your stocks

I cannot help you with this. I only buy such stock for personal use. Such requests in threads are also outside AK rules. I suggest you pursue the link/image you posted earlier.

 

[kevzep]

i think this guy from Japan don't want to share his experience that's why all label on new transistor are hidden.

Of course, many people like to play that sort of thing close to the chest.....

 

[petehall347]

you could narrow it down quite a bit by putting the specs of the originals into a suppliers search system . then see if suitable for audio .. this sort of thing takes too much of my time up .