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Old 21st January 2011, 05:21 PM   #1
studeb is offline studeb  United States
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Default Replacing NPN, do i care about hFE?

I am replacing some 2sc458 NPN transistors with 2sc2240 in a tape playback amp. And wonder about the grades to use. On the schematic the hFE grades for the 458 are C 160-320 and D 250-500. For the 2240 the grades i have are GR 200-400 and BL 350-700.
Should I replace with GR or BL? Higher hFE would give more gain or? But then would this through off the eq? Or am i bass ackwards again? Does it matter as i will have to set the PB level and EQ anyways?

FWIW the 458s i pulled measured 200+/-10 on my multimeter. I know that is not an accurate way to measure, but it could be used to group them. The 2240s come in at 200 +/- and 400+/-.

Thanks for any advice.

For reference here is the PB circuit, i marked red circles on the in and out
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Old 21st January 2011, 05:23 PM   #2
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It's not critical at all. Looking at the grading numbers, I'd go with the lower gain units.
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Old 21st January 2011, 05:55 PM   #3
kevinkr is offline kevinkr  United States
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Quote:
Originally Posted by bob91343 View Post
It's not critical at all. Looking at the grading numbers, I'd go with the lower gain units.
Certainly safer from the standpoint of stability..
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Old 23rd January 2011, 03:09 AM   #4
studeb is offline studeb  United States
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Thanks for the help. Lower gain it is then.
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