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Transistor Substitutions

KSA1220/1220A for the 2SB631, and
KSC2690/2690A for the 2SD600.

But the originals -look- fine, a little discoloration of the metal is normal. Have you tested them and found them defective?
 
I suggest that you be very, very careful around those trimpots because they tend to completely fall apart with age.

you may want to Deoxit them, put the wiper roughly back to to roughly the same spot... but they may fall apart.

I’m OCD and replace those kind of trimpots on sight, but not everyone is as fanatical as I am. ;)
 
Saintintn said:
Thank you so much. I have only tested for voltage at this point. I've got 26V DC coming out of my speaker terminals and I'm trying to pin it down.
Click to expand...
Pull the output transistors and test them for being shorted. Then you'll need to start a thread of your own in the Sansui forum to pin down the issue(s) causing the 26v. There is no speaker protection relay in the 3900Z. There are many Sansui "experts" in that forum to assist.
 
rwwear said:
According to Motorola the 2SB631 replacement is the 2N4920 and the 2SD600 the 2N4923.
Click to expand...
The KSA1220AY (PNP) and KSC2690AY (NPN) are virtually perfect substitutions. Both are TO-126 packages.Depending on the circuit, the faster ft may not be an issue at all.
https://www.el-component.com/bipolar-transistors/2sd600
https://www.el-component.com/bipolar-transistors/2sb631
https://www.el-component.com/bipolar-transistors/ksc2690a
https://www.el-component.com/bipolar-transistors/ksa1220a
 
Try to find the replacement of these for my Onkyo TX 560
These are Q501 and Q502 on the driver amp board and assumed to be the differential pair, not quite sure. I am trying to correct the DC offset even the number are not that much off. 32mv on one side.

upload_2020-11-2_17-23-54.png

The part list show them as 2SC1000 (0-1), what does this (0-1) mean? The 2SC1000 are one of the top 10 worst transistors.
But the actual ones on the board has GR mark on top, T, 5F/C1681 mark on the side.
What should I replace them with? Should I just use the substitute for 2SC1000 such as KSC1815Y? or substitute for C1681? and what are these would be?
Thanks.
 
I think the KSC1815YTA would be a better parametric match than the KSC1845. In either case, if you are trying to match for minimum output offset, then you will need to order at least 10 and then pick two with the closest Vbe match you can find in the group.
 
The SM shows 2SC1000 (0-1), the actual parts on board are C1681; and I assume it is better to use substitute for what is currently installed on board? And that would be KSC1845? I am confused.
 
I looked at the specs on the 2SC1000, and noted 50 volt, 100 mA
KSC1845 is 120 volt, 50 mA
KSC1815 is 50 volt, 150 mA.

The circuit appears to put no more than 40 volts across the part, and the current appears to be around 1.1 mA per parts, so either will be OK. If these were PNP, then the KSA992 would be a commonly suggested replacement - and the complement to the KSA992 is the KSC1845. So I'll change my recommendation to the KSC1845.
 
EC1 said:
The SM shows 2SC1000 (0-1), the actual parts on board are C1681; and I assume it is better to use substitute for what is currently installed on board? And that would be KSC1845? I am confused.
Click to expand...
They just made a substitute at the time of production sometime after the schematic was published. You'll find a LOT of brands/models have many in-production changes that are undocumented. It's common. Always go by what is in the stock unit and make substitutions/replacements from there. The (0-1) after the transistor number is the gain group they wanted to use for that particular transistor. Different transistors and makers will use differing numbers, or letters to designate their gain groups. The KSC1845FTA is the preferred substitute in this case. The (F) is the gain group, and the (TA) means TApe packaging. You should gain match the input pair to help equalize DC Offset.
 
Thanks all for the information for the beginner here. I do have some KSC1845F here just need to find the matching pairs.
So the “GR” printed on top is also the grade indication? And how to find out what that is, in general in order to find the matching substitute?
 
Skywatcher said:
You should gain match the input pair to help equalize DC Offset.
Click to expand...
Not to open a can of worms here.... Ideally, you want to match both hFE and Vbe. If your goal is to minimize DC offset, then I think Vbe will be more important. hFE will affect offset even with perfectly matched Vbe's, but it is a secondary effect created by the base currents in the base resistors.
 
Did order a vbe tester supposed to measure the Vbe, will see how that works.
My dc offset is not perfect but acceptable. Just want to explore and learn.
 
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