goat67
Addicted Member
It is kinda hard to verify the transistors, if you did not record how they came out you will need to use the schematic to verify.
Soundcraftsman RA-7502 Resurrection
- Thread starter Young46
- Start date
As always....
OP Jerry -- goat67 --- Is one of the more knowledgeable techs with SC amplifiers.
Please see the first post on this thread and the photos I’ve posted.The amp has been sitting idle for a couple of years. When I tried to power it up, the lamps would just randomly light up. A friend gave it to me and he said it wouldn’t work and that the lamps would just randomly blink. The parts list I got from reading some past forums. I’ve installed the new output transistors. I did mark the old ones when I pulled them. I hope the new ones I purchased are correct. I mentioned replacing the mps and a93 transistors. They are not that expensive and I guess which camp your in they should/should not be replaced. One camp seems to believe shotgunning is the best approach while the other seems to want to leave them in if they are ok. They are old so I lean toward replacing them while the boards are out and accessible. Thanks for the response.
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Yes, the lights do as you describe. Nothing obvious on the ps and light boards. I checked all lights individually and they all light.
Thanks. I have the caps for the power supply boards and have already recapped the amp boards. I’m working my way from the back of the amp to the front. I’m not 100% sure it doesn’t work but those lights doing what the did was troubling to me. Again, I’m just a hobbyist, not a professional tech. If you would not mind could you verify the Darlington pair output transistors I chose. Are they suitable replacements?
goat67
Addicted Member
Part numbers please
Mouser #:
863-2N6284G
Mfr. #:
2N6284G
Mfr.:
ON Semiconductor
Mouser #:
863-2N6287G
Mfr. #:
2N6287G
Mfr.:
ON Semiconductor
Mouser #:
863-2N6284G
Mfr. #:
2N6284G
Mfr.:
ON Semiconductor
Mouser #:
863-2N6287G
Mfr. #:
2N6287G
Mfr.:
ON Semiconductor
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Sorry for the delay. The 2n6287G's were not available so I used the 2M6286G's. Was that not a good choice? I also found a MPSL01 that was bad. Is there a better substitute available now than the MPSA43? Mouser does not have a MPSA43 stocked. They have MPSA43-AP in stock. Is it suitable.Part numbers please
Mouser #:
863-2N6284G
Mfr. #:
2N6284G
Mfr.:
ON Semiconductor
Mouser #:
863-2N6287G
Mfr. #:
2N6287G
Mfr.:
ON Semiconductor
goat67
Addicted Member
The HFE for the 2N6286 is 2400 opposed to the the 2N6287 of 4000, Will this be an issue? I am not sure I do know the 287 are in stock at Mouser now. For the MPSL01 since you did not identify where it is used I can only offer generalities. The MPSA43 is a valid sub better would be a KSC2316YTA, if Gain is important use ZTX694B or ZTX696B
Thanks. It sounds like I may need to order the 2n6287's? I still have the unit apart and they would still be fairly easy to replace. I have some ZTX694B's in my stock.
"The HFE for the 2N6286 is 2400 opposed to the the 2N6287 of 4000,"
Well, now I am confused. If the NPN 2N6284 is the complimentary to the PNP 2N6286, 2N6287, wouldn't the 2N6286 be the better match since the HFE is the same (2400) for these? Remember, I am a amateur hobbyist so am easily confused.
Well, now I am confused. If the NPN 2N6284 is the complimentary to the PNP 2N6286, 2N6287, wouldn't the 2N6286 be the better match since the HFE is the same (2400) for these? Remember, I am a amateur hobbyist so am easily confused.
goat67
Addicted Member
Sorry for the confusion.
I should not post so early in the morning Disregard the HFE statement as it is wrong I misread the datasheet. what is important is the voltage ratings and type of the 3 part numbers.
2N6284 is a 100v PNP with an HFE of 2400
2N6286 is a 80v NPN with an HFE of 4000
2N6287 is a 100v NPN with an HFE of 4000
so as I originally posted use the
2N6284 100v PNP
and
2N6287 100v NPN
So the PNP has a lower HFE spec than the NPN so we can safely say having matching gain is not important in this circuit design.
I should not post so early in the morning
Disregard the HFE statement as it is wrong I misread the datasheet. what is important is the voltage ratings and type of the 3 part numbers. 2N6284 is a 100v PNP with an HFE of 2400
2N6286 is a 80v NPN with an HFE of 4000
2N6287 is a 100v NPN with an HFE of 4000
so as I originally posted use the
2N6284 100v PNP
and
2N6287 100v NPN
So the PNP has a lower HFE spec than the NPN so we can safely say having matching gain is not important in this circuit design.
Racingh11
Super Member
I just saw this thread and I'm thinking you are past this point... But as far as transistors for the L01 and A93 goes, there are a couple options. For me I set them up 2 different ways depending on what the amp will be used for; home or mobile/commercial/heavy duty. I set the home up for best quality available and the mobile for better durability. For home I use KSC1845 for Q1,2,3. The first 2 being matched for the differential input. The KSC1845 are specific for audio and low noise. They are more linear in the 0-3mA current this circuit operates in. The stock L01 are a general transistor and a heavier current and wattage and almost too much for the input. The KSC1845 still has a collector current rating of 50mA, which is plenty to handle 3mA. It also has a high gain like the ZTX694B. But the ZTX694B is not meant for audio and is more of a switching transistor. And it's linearity drops at the load current they are used at in this circuit. NOTE**:The KSC1845 does not have the same lead order and must be turned at an angle and leads turned to use them(L01 is EBC and KSC1845 is ECB, both TO-92 case). For all other L01, I use 2N5551. including the pre-drivers. For the A93, I use 2N5401
For heavy duty applications I like to use all 2N5551 for the L01. They are better than L01 in pretty much all specifications and more durable than KSC1845. From higher voltage to more linear, or less output capacitance, etc. 2N5551 and 2N5401 are low noise also even though they are not specifically listed as such. If I were to use Zetex brand, I would go with ZTX696B for L01 and ZTX796A for A93. They have more linear gain in the low current used and actually have a higher voltage than the ZTX694B, and also have high gain. But again, none of the Zetex are specifically meant for audio and are more for switching applications,etc.
For the 2N3440 and MM4003 voltage and driver stages, you can use the still available 2n3440, and 2N5416 for the MM4003.
Outputs I would go with the MJ series ON Semi stuff like you had shown or newer.
Also Q1,2,3 are usually still intact and the junctions will test fine, but the gain will be in the single digits or none at all. These things just idle too much and degrade over time. The first pair of 2N3440 and MM4003(Q4,5) also idle at low current and tend to have low gain after years or use. Might as well figure on replacing Q1,2,3 either way. Especially if you have DC offset or a lot of noise.
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Sorry for the confusion.
I should not post so early in the morning
2N6284 is a 100v PNP with an HFE of 2400
2N6286 is a 80v NPN with an HFE of 4000
2N6287 is a 100v NPN with an HFE of 4000
so as I originally posted use the
2N6284 100v PNP
and
2N6287 100v NPN
So the PNP has a lower HFE spec than the NPN so we can safely say having matching gain is not important in this circuit design.
Thanks goat67 and Racingh11, I have the output transistors 2N6284 and 2N6287 you recommended installed. I recapped (electrolytic) all the boards. I installed new 2n3440 and 2n4516 transistors. I installed new MJ21195 and MJ21196. Installed the KSC 1845's in Q1, Q2, and Q3 as recommended by Racingh11. When I power up, I still get intermittent very short burst of the lamps on both channels. No smoke anywhere though so that's a good thing. I don't have an operators manual or instructions so I am not sure how to hook up components. I read the thread on the jumper but am confused.
My A5002 does that at power up as well. I attributed it to the crowbar circuit resetting.
So, is it normal? Or nothing to worry about?
I don't lose any sleep over it.
