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I need a modern substitute for a couple of old transistors. Would prefer standard generic rather than an NTE part.
They are two audio transistors from an old reel to reel in the final output stage, so just audio.

2sc644 (or 2sc900)
and
2sa564 (or 2sa750)

Does anyone have suggestions that Digikey might have?
« Last Edit: May 07, 2012, 10:04:02 am by db2db » Logged

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2sc644 is a small signal low noise NPN silicon planar transistor. I would use BC184 or BC549.

2sa584 I can't find any data on, but I found a table that suggests BC557 as a replacement.

Be aware that these replacements may have different pinouts.
« Last Edit: May 07, 2012, 04:07:06 am by dc42 » Logged

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ok, thanks. They both look pretty basic, so I'll see how that goes.
What are the important specs to match when subbing a small transistor?
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What are the important specs to match when subbing a small transistor?

I want the same polarity (PNP/NPN) and preferably the same or similar case style and pinout. I want the substitute to have the same or greater Vceo(max), Ic(max) and max power dissipation, unless by examining the circuit I can put upper limits on the actual voltage, current and power that the transistor will experience. I want the hfe of the substitute to be quoted at similar Ic to the original, and to be in a similar or slightly greater range. If the transistor is in a preamplifier or amplifier input stage, I want the noise figure of the substitute to be no higher than the original.

In switching applications, I would look at Vce(sat) too.
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2sa584 I can't find any data on, but I found a table that suggests BC557 as a replacement.


Well no-one's mentioned that device so that's no problem.  What about the 2SA564/2SA750 though ? smiley


2SA564 is PNP, 25V, 50mA, 0.25W, hfe > 65 @ 2mA, Vsat 0.4V at 50mA, fT=150MHz, noise factor 2+dB
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OK, I mistyped, I meant 2sa564. From the data you gave, BC557 still looks like a suitable replacement. It has a higher hfe, but that's not likely to be a problem in a professional design.
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Thanks everyone.

I ordered:

2SA564 (original)
2SA992
2SC2240
2SC536

Hopefully one pair of those will work well.

« Last Edit: May 11, 2012, 01:41:47 pm by db2db » Logged

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