identifying a transistor from a 70s microphone

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Deadpidgeon37

Joined Oct 21, 2023
3
i have a sony stereo electret condenser from the 70s. one of the transistors has failed but i cannot identify the transistor. can anyone help?
the code reads K39A CI2
IMG_20231021_175205.jpgIMG_20231021_175214.jpgIMG_20231021_175220.jpg
the microphone is an ecm 99 if that helps.
 

dl324

Joined Mar 30, 2015
16,684
do you know where I can buy one of those or the modern equivalent?
I found this cross reference:
1697988255203.png
at https://masterelectronicsrepair.blogspot.com/search?q=2SK39A

I looked up specs for 2SK103 and found:
1697988217343.png
at https://www.web-bcs.com/transistor/tfet/2s/2SK103.php?lan=en

That lead me to Vishay J102, which is obsolete, but Mouser has some J201 from InterFET that look compatible:
https://www.mouser.com/ProductDetail/InterFET/J201?qs=OxRSArmBDfyvD8SbvWteMw==1697990095365.png
1697988505657.png

You can get a surface mount device for 10% of the price of the through hole part.
1697988447927.png
You can get these adapters for about a dime:
1697989059515.png
The leadframes are a dime each, if you can find them. You can substitute right angle male headers if the holes in the board are large enough. If it's a single sided board, you could enlarge them with a 0.035" (#65) drill bit.

If you have some copper clad board and a Dremel tool, you can make your own (shorter ones):
1697989740221.png
 
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