tusntuk2

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A constant topic - transistor substitution. I needed a sub for a 2sc1222, and as the dates on the threads change, so do the answers. Some is due to obsolescence, of course, but it is changes due to the understanding of how the transistor is applied in the circuit that seem the most important - only I don't always know what that is.

The 1222 is in the muting circuit of a Kenwood KA-3500. Suggested substitutes have included these: KSC945C, KSC1845FTA, KSC2383YTA, KSC2690AYS, and ZTX694B. Pull them all up at Mouser to compare, and you get quite a range of numbers. Now the question - what numbers are the most important when choosing the best substitute? and, how do I tell?

Still learning! Thanks...
 
A terrible answer I have to your question is that it depends.
KSC1845 should work fine, it's the go-to along with it's compliment KSA992 for small signal transistors.
 
Thanks, Ivan, that's what the question is - on what does it depend? I have used three different subs for the 1222, and they all seem to work. I don't know which one is best, or if it will hold up in the muting circuit. I also read comments like, "...(Kenwood) must want a higher gain here.." or "...probably needs to handle more current..." or "..the 2383 is beefier..". That's what I'm trying to learn, is how to select one over another.
 
Hi,
When picking subs for transistors, I make sure that
the rated voltage C to E of the replacement is at least as high as the one I am replacing.
that the Gain, or HFE is similar
that the rated current is at least as high if not higher than the one I am replacing.
And if it is a small signal preamp type transistor I attempt to replace with a similar "Low Noise" type transistor.

I always look at the current rating is the highest priority, followed by voltage C to E (sometimes referred to as VCEO)
low noise type is important if the replacement is for a preamp.
HFE is nice to have, but if it is a preamp for example, they usually are low noise high gain (HFE) devices

And of course case style matters big time when it is outputs being replaced, and they need to be the same case style as in T03 etc.
 
ah, thanks Tom! That's a good start. Now when comparing the 1845, the 945 and the 2383 I can understand "beefier" meaning higher Vcbo and Vceo. When comparing these specs to the original 1222 I see that all 5 of those named have higher numbers across the board, suggesting the 1222 was the "smallest" of the group. Widest differences seem to be in Hfe.

Now to understand when Hfe is important to consider and when it is not as important. Must be the "that depends" part!

Thanks, Ivan for the 1845 recommendation, I have some in stock. It seems like a stronger choice than a KSC945, which most closely resembled the original. I think the muting circuit intends to spare the speakers from the on/off "thump", as there is no relay in this amp. So in this case stronger would be better, no?
 
you also can download the manual at eserviceinfo.com

The parts list suggests the 2sc1345E as substitute where (E) means the 400-800 HFE group, where another transistors substitute is called a generic 2SC1345. So, in the circuit as is, HFE may be important.

to give some extra food for thought.:) (as more info usually adds to the confusion)
 
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