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Old 3rd March 2014, 10:33 AM   #1
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Default Kenwood KA5700


I am looking for a replacement for the power transistors for this amp.
They are 2SB617A and 2SD587A. They are obsolete locally. Can someone please assist


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Old 3rd March 2014, 11:11 AM   #2
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Send a message via Skype™ to JonSnell Electronic
This may help you find equivalents;
2SB617A Datasheet & Equivalent - 2SB617A Transistor DataSheet PDF. Parameters and Characteristics. Electronic Component Catalog
www.flyingmole.co.uk For World Wide support for Flying Mole, Class D, Refurbishment and Repairs. www.jonsnell.co.uk
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Old 3rd March 2014, 11:56 AM   #3
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Originally Posted by JonSnell Electronic View Post

Thanks alot Jonsnell


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Old 3rd March 2014, 02:09 PM   #4
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Sorry, but you're sort of screwed. That type of transistor package (sometimes called "batwing") hasn't existed in a long, long time. You'll have to modify the heatsink to accept TO220 transistors instead. Drilling is all it takes, basically.

With TO220, you will have tons of options. Most widely available is TIP31/32C... Probably not a great replacement, but it'll work and is very cheap and easy to find.
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Old 5th March 2014, 08:36 PM   #5
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Originally Posted by Welcome View Post
With TO220, you will have tons of options. Most widely available is TIP31/32C... Probably not a great replacement, but it'll work and is very cheap and easy to find.
I guess you meant TIP41/42C, which would fit basic Vceo and Ic requirements (though a fair bit slower). The 31/32 are 3 amp parts.

Something like 2SC5198/2SA1941 would be interesting - faster, higher Ic, better SOA. Sanken's 2SC4467/2SA1694 and 2SC4468/2SA4468 would be worth looking at as well. These are TO-3P parts.
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Old 6th March 2014, 04:23 PM   #6
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Sorry, you're absolutely right.

The TO3P devices may be a bit trickier still to install. The heatsink arrangement is a bit awkward with the legs going through that slot which would have to be widened I think. TO220 would just require that one screw hole on top, as that transistor size is basically the same as the original "batwings".

Click the image to open in full size.
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Old 11th March 2014, 01:42 PM   #7
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lets behave now people ....

None or any other transistors suggested is a drop in replacement ...

Even if you find new ones that are original still those are not drop in replacement

The specific amplifier doesnt feature a trimmer to adjust the bias ..Obviously if you replace the outputs with TIP models these will blow with in first 10 minutes ...

To accommodate any transistor of your choice first you need to replace resistors in the bias scheme with a trimmer to be able to adjust bias to the required point ...

Secondly the output transistors is not only a question of voltage and wattage of speed (ft) but mostly how these are possible to be driven by tiny little drivers existing inside the 5700.....especially when those will be called to drive a huge capacitance ...

If you decide to replace the drivers also then VAs has not enough guts to drive the drivers and so on and on and on ....

Messing around with the wrong types of semis will easily drive a semiconductor based amplifier to oscillation with catastrophic results ...compensation will also need to be altered

Let us not forget that these NEC semis was so easy to drive so the requirements behind them was very very low

On the useful side i have successfully worked out a 5700 in the past that was burned totally by using 2SC4467-2SA1694 for outputs , replacing also drivers with a bit bigger like 2SB 560 and 2SD438 , also replaced the trimmer with something that i dont remember

Again let us not forget that at this age a 5700 will also need a complete recapping

Kind regards
been there Sakis
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