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Fixing old gear / Transistor problems
Fixing old gear / Transistor problems
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Old 8th February 2003, 07:40 PM   #1
OliverD is offline OliverD  Germany
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Default Fixing old gear / Transistor problems


when fixing amplifiers, I often encounter the problem that many transistors widely used in old gear are now out of production. Often they are available somewhere but the probability of getting counterfeit devices is quite high. That's why I always stock some standard parts like BC550 / BC560, BD139, BD140, MJE340, MJE350 for driver and input stages and a collection of power devices in various cases.

However, when fixing vintage high end amplifiers, I don't like the idea of substituting those cheap "one for all" transistors.

As it is hard to find more than polarity, Pd, Vce and ft data of old transistors, I'd like to ask the more experienced here on the forum what their suggestions for proper replacements would be:

original -> replacement

2SK240 / 2SJ75 -> 2SK389 / 2SJ109 (???)
(Didn't find any datasheet for Dual JFETs)

2SC3281 / 2SA1302 -> 2SA1987 / 2SC5359
(This should work fine IMHO)

2SK213 / 2SJ76 -> IRF610 / IRF9610 (???)

2SA1142 / 2SC2682 -> ???

2SA1145 / 2SC2705 -> ???

Does anyone have datasheets of those old devices? What modern devices would you suggest as a drop-in replacement?

Thank you!
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Old 8th February 2003, 10:06 PM   #2
EchoWars is offline EchoWars  United States
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Most transistors nowadays are quieter and can handle more power, and have better gain than the old stuff. For the most part, there are good reasons why a component was obsoleted.

For instance, I have actually had to replace a few 2SA1142's in an amp recently. I stuck in a 2SB649A and forgot about it (the 649A is Vceo 160V whereas the 1142 is Vceo 180V, in my application it didn't matter).

On a slightly different matter, I notice your nick "AMT-freak". Posted a question in the speaker forum regarding newer Heil's that I'd hope you'd take a look at.

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