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Old 10th November 2010, 12:08 AM   #1
jgray is offline jgray  United States
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Default Fairchild FJA4310

Hi. I am working on a somewhat low power class A amp, and considering the Fairchild FJA4310 NPN BJT for the output section. Does anyone have experience with this part and its suitability for an application like this? The beta droop looks good in the datasheet.
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Joel
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Old 11th November 2010, 01:19 AM   #2
jgray is offline jgray  United States
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How about the 2SC5242 instead? That one looks even better.
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Old 11th November 2010, 01:53 AM   #3
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In what way ?
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Old 11th November 2010, 02:51 AM   #4
jgray is offline jgray  United States
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Even more uniform gain as collector current varies.
Joel
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Old 11th November 2010, 03:48 AM   #5
CBS240 is offline CBS240  United States
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How much power do you expect from this amplifier and into what load Z? Seems heat dissapation would be the primary concern of a class A OPS, so bigger transistor less worries, eh? How about FJL4315?

Hmmm, it appears that same die comes in diffferent packages, ....for a different price I'm sure.
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Last edited by CBS240; 11th November 2010 at 03:55 AM.
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Old 11th November 2010, 05:28 AM   #6
AKSA is offline AKSA  Australia
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I've always found mosfets better for Class A; they handle the thermal abuse easily......

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Old 11th November 2010, 05:26 PM   #7
jgray is offline jgray  United States
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CBS240...The supply is +/- 12.5 V rms and currently the output is biased at 1.0A, and running into 8 ohms. I am currently using two 2N3715 (push pull) in a TO-3 package, and fairly happy with the waveforms, and the sound. I am looking to improve the audio performance, and also switch to a TO-3p package for mechanical mounting reasons.

It looks like the FJL4315 would handle even more power and the gain curve is similarly flat, although as you can tell from my little supply, I don't think I will pushing any of these devices to their limits for temperature and power. I'm sure you're right about the price too!

Thanks,
Joel
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Old 11th November 2010, 05:29 PM   #8
jgray is offline jgray  United States
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AKSA...I am sure you are right about the mosfets and thermal abuse. I still have a lot to learn about them before I would try and design them into an amp. That's on my list of things to explore after I finish this amp. Well actually, I have an old tube radio to restore next, but then on to the mosfets!
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Joel
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