2x 2Sk170 in place of 2SK389 and 2x 2SJ74 in place of 2SJ109? - diyAudio
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Old 16th July 2007, 03:12 PM   #1
jarthel is offline jarthel  Australia
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Default 2x 2Sk170 in place of 2SK389 and 2x 2SJ74 in place of 2SJ109?

I've seen a reply where someone said it's okay to replace a 2SK107 with 2SK389 (same for 2x 2SJ74 in place of 2SJ109) but I want to confirm.

Also why is there a need to glue them? I saw this photo: http://www.diyaudio.com/forums/attac...amp=1171282640

The transistors are facing each other. But since I want to replace a 2SK389 with 2SK170, I cannot have them facing together unless I bend the pins to make it work?

thank you for the help
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Old 16th July 2007, 03:17 PM   #2
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yes, it's okay to use the single versions.

The devices are glued together for thermal coupling, which improves the degree to which the can be matched (not the best choice of words, but you get my drift).

I'd recommend about 15 of each single version to find 1 closely matched pair, as in my experience these can vary widely even with the same grade.
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Old 16th July 2007, 03:36 PM   #3
jarthel is offline jarthel  Australia
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I already have matched pairs. does this mean I do not need to glue them?

thanks again
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Old 17th July 2007, 08:19 AM   #4
h_a is offline h_a  Europe
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C'mon! You need thermal coupling, otherwise your matched fets are going to drift thermally -> they're no longer tightly matched.

That's the reason the 2SK389 is a double package, tight thermal coupling and best matching since both fets are sitting next to each other on the wafer.

Don't worry about glueing them together. It would be nice todo if possible, but if you don't need the last bit of performance (then the 2SK389 would anyway the only choice) put them in and that's it.

Cheers, Hannes
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Old 22nd July 2007, 12:48 PM   #5
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fun stuff, watch the production date code : here
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Old 25th July 2007, 03:46 PM   #6
h_a is offline h_a  Europe
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Oh Jacco, excuse my ignorance, but I fail to understand the production code. The datasheet also gives me no clue about what '7E' might mean.

Struck the lightening please. Cheers, Hannes
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Old 25th July 2007, 03:53 PM   #7
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Is that supposed to mean they were 'produced' in 2007?

I guess if they're fakes, it would be true, since they probably were made this year.
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Old 25th July 2007, 04:03 PM   #8
uli is offline uli  Austria
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Bought lots of SJ109 in 2004 - 2005, some of them carry 7E

does not mean 2007

Uli

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Old 25th July 2007, 05:18 PM   #9
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NEW/NEU ones from May '97.
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Old 26th July 2007, 08:48 AM   #10
h_a is offline h_a  Europe
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Isn't it the same for Jfets as for wine?

The older it gets the better it is
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