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Old 8th November 2002, 12:42 AM   #1
biff584 is offline biff584  United States
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Question transistor substitutes

I am building an Elliot P3A amplifier - 100 watts into 8 ohms. I was planning on using the ON Semi MJL3281A/MJL1302A pair for the output transistors, but I am having difficulty getting the MJL3281A since my sample order is backordered and I don't want to spend alot of money.

I may switch to either the MJ21193/MJ21194 OR the MJ15003/MJ15004 (both also ON semi). The transistors can be found at Anyone have any comments on these pairs- is one better than the other? Also, the original set I had planned on using were TO-220 Flatpacks and the other substitutes are TO-3 cased- is there any benefit either way?

Thanks alot.

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Old 8th November 2002, 01:30 AM   #2
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The MJ21193/4 pair is newer and has better SOA than the MJ15003/4 - I'd use those, as the price is pretty much the same either way.

It should be noted that the 21193/4 series comes in a TO-264 package as well - they're called the MJL21193/4 (note the added "L") - those would be ideal replacements for the Toshiba transistors if you could find them.

As far as I know, the same physical transistor die is in both the MJ21193/4 and MJL21193/4 - the only difference would be thermal resistance and physical ruggedness. Which one is better would depend on your mounting method and the amount of torque you can apply. I'd personally go with the flatpack (MJL) ones, as you can use them with Rod's PCB layout, and you can use a u-channel to apply a nice, even amount of mounting force without warping the package or lifting it from the heatsink due to the uneven force placed when you use the mounting hole.

At any rate, any of these would be fine replacements - the motorola/OnSemi transistors will be a little more rugged, all else being equal, but they won't have the gain linearity of the Toshibas. Since the amp has no short circuit protection, i'd go with the MJL21193/4 because I like the extra SOA (safe operating area.)
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Old 8th November 2002, 02:45 AM   #3
biff584 is offline biff584  United States
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Default Thanks

Thanks alot for the response- I appreciate your help.

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Old 8th November 2002, 03:20 AM   #4
BrianGT is offline BrianGT  United States
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Remember that you sample order will eventually come, and you can swap the transistors out later. It took them a few weeks to get me my 3281 devices. How many total do you need? I might have some extras if you don't need too many.

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Old 8th November 2002, 11:00 AM   #5
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Hi biff584,

I'm building a P3A as well (slowly) and I'm going to use Toshiba's 2SC5300 and 2SA1943 as these are the replacemnets for 2SC3281 and 2SA1302. Hope I got the "C" and "A" around the right way.

I'm currently using the 2SC5300 and 2SA1943 in my AKSA and am very happy with the result.
Greg Erskine
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Old 8th November 2002, 04:37 PM   #6
mlloyd1 is offline mlloyd1  United States
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I'll be looking forward to hearing your opinions about the sonic differences between the AKSA and Project 3A. I bought some Project 3A boards to play with building over the holidays.

Originally posted by grege
Hi biff584,

I'm building a P3A as well (slowly) ....
I'm currently using ... in my AKSA ..
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Old 8th November 2002, 09:54 PM   #7
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I am using MJ15003/15004's for my modified P3a, when I get around to finishing it (I could any time, but I'm busy with other things, like pulsed power). That seems to be what everyone uses, so they couldn't be too bad. It will be interesting to see how this amp compares to an normal P3a (I've added a current mirror among other things).

I've heard that those Toshibas are a bad choice for CF designs. Any comment on this?
- "With power amplifiers, negative feedback is a good thing, and positive feedback can induce destructive oscillation, but with people, positive feedback is a good thing, and negative feedback can induce destructive oscillation"
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