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Sansui 3000A transistors

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danqth

New Member
Hello all,I am new to this forum.I have a 3000A since 1969 USAF SE Asia.It failed about 30 years ago-protector light on. It has since been on a shelf in the basement till about two weeks ago.I decided what the heck and jumped into it.So far I replaced one power supply elec. cap 3000uf 50v with a 1500uf 50v I had on hand to prove it was bad,it won't stay in when I get the right one.I also found one power transistor B170008 and a pre power 2sc756 that are both shorted in the left channel.I am having trouble finding the transistors.I am hoping someone can help with a source for them or suggest a replacement.Thanks in advance. Dan
 
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Use these:
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=MJ21194GOS-ND

For the caps, use:
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=P6940-ND
You need 4 because the unit has dual supplies.
Note on this receiver there is a factory modification that MUST be done in order for it not to blow up again. I do not remember all it entails but I think the bulletin is available and I think someone here has it. One thing I do know, if your receiver has electrolytic caps in series with the outputs (they are mounted underneath the chassis) then you have the mods. These are not shown on the schematic, so you will have to look for them and trace the wiring to be sure. The reason for this is the output stage is very difficult to stabilize so that there is 0VDC on the output, and this DC drift can damage your speakers and the amp. If you do have the caps you should replace them for best sound, and if you don't have them you will have to add them.
 
Thanks for the reply,I will order them.Do you have any idea about the 2sc756 or a sub.I have the info. for the mod and will order those parts as well.I bought the 3000A new way back when.It had a great sound as I remember it.Now to look for a pair of AR3 or AR4 if I am real lucky at a sale. Thanks again.
 
Anyone have anything on the 2sc756 pre-amp transistor or a sub.It's the only component I have not found.Thanks again
 
I have a sub, I meant to get the part number last night and ran out of time. I'll try to get it tonight.
 
Thanks dr*audio and wianieq for your help.I will post and let you know how the repair turns out.Maybe some photo's if I can manage that.Thanks again. Dan
 
The parts finally arrived,so I can get to the repair.Does anyone know if this receiver has a way to adjust the DC offset.The service manual does not mention it only the bias adj.Now back to the repair.Thanks again
 
The way the 3000 is set up, there are 2 bias pots for each channel, and each adjusts one output transistor, but they both affect each other as well. They also affect the DC offset. These pots are critical for proper operation, and if one goes open you can get a large DC offset and lots of current, and the amp blows up. Check your pots with an ohm meter. If they are flakey, you will have to replace them. They carry quite a bit of current, so you would have to find at least a 1/2W pot to replace them.
When you adjust the bias, follow the procedure in the manual. Then you can trim one of the pots for 0V on the output. If your receiver has the output caps, you will have to measure the voltage on the input side of the caps.
 
The 3000A is finally finished.Replaced the power and pre power transistors,the power supply caps and did the mod to help prevent output failure and fried speakers.Also repaired the protector circuit,bad transistor.It now sounds I believe like it once did,crisp and clean.Not bad for 40 years old.Now the search for a pair of classic speakers-Sansui,AR,Pioneers etc.Hopefully at a garage sale or thrift shop.Thank you to all for your help. Dan
 
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