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Old 2nd February 2009, 05:53 PM   #1
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Default Mj15003

Hello all:

I saw in a previous thread something about replacing all MJ15003's with MJ15024's. What would be the main reason for this? Are they more efficient, less heat for the same amount of power, or is it something else?

I have an old Peavey bass amp head that uses the "common" (I gather) 400BH amp section. Its all working fine, I just dismantled it to clean and thought I would look up what people thought about this amp.

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Old 2nd February 2009, 06:07 PM   #2
wg_ski is offline wg_ski  United States
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They're easier to get. In most circuits which use the MJ15003, the MJ15024 is suitable. The MJ15024 can handle higher power at higher voltage before burnout but behaves similarly. The amp won't generate any more or any less heat either way. Only replace them if their either dead or suspect (if their neighbors died).
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Old 2nd February 2009, 06:17 PM   #3
ppa is offline ppa  Italy
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moreover Mj15024 is more fast
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Old 2nd February 2009, 06:20 PM   #4
wg_ski is offline wg_ski  United States
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People make it seem like a 2MHz fT vs a 4MHz is a big deal. In classical circuits, it's NOT.
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Old 2nd February 2009, 06:29 PM   #5
lineup is offline lineup  Sweden
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They are almost like twins, MJ15003/04 and MJ15024/25
Slightly faster is MJ15024/25, but for an output follower this is no issue.

MJ15003/4 on the other hand, has got lower saturation voltage for putting out current.
Vsat.
This is maybe more important in some power amplfiers.
To avoid clipping too soon at high current output.

---
Vsat = the minimum voltage across Collector-Emitter at specific current level.
This is shown in datasheet diagrams.
MJ15003 datasheet download

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Old 2nd February 2009, 07:36 PM   #6
ppa is offline ppa  Italy
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Quote:
Originally posted by wg_ski
People make it seem like a 2MHz fT vs a 4MHz is a big deal. In classical circuits, it's NOT.
Yes, I confirm, but in a circuit such as stasis of Mr.N.Pass, for example, I choose fast transistor than mj15003............
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Old 2nd February 2009, 08:05 PM   #7
pooge is offline pooge  United States
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The MJ15024/5 probably has less beta droop, but the specs on the MJ15003/4 aren't as well characterized. The first has a higher voltage rating than the later, but the later has a higher minimum hfe specification. The application would dictate which is better.
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