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MiniMax HeatSink - Power Transistor Question

post #1 of 10
4/17/09 at 10:10pm
Thread Starter 
I am now at the point where I need to mount+solder the transistors and the heatsinks on the board. Do I need to put both transistors that are in the QB8/9 R/L position or only mount one of them ? It is not clear because, according to pictures on the diyforums website, it looks like only one of them is mounted/soldered but I'm not sure. I don't want to continue and ruin everything
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post #2 of 10
4/17/09 at 10:19pm
One transistor per heatsink.
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post #3 of 10
4/17/09 at 10:21pm
Thread Starter 
Ok, but at position QB8L for example, there is some place on the right for another transistor, do I need to solder it too (no HS) ? Or just the one that is mounted on the HS ?
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post #4 of 10
4/17/09 at 10:40pm
no, just one (and make sure it's the correct one)
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post #5 of 10
4/17/09 at 10:45pm
Thread Starter 
I mounted the MJE243 NPN and the MJE253 PNP, should I mount the BD137/138 instead ? Or I just have to chose one or the other ?
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post #6 of 10
4/17/09 at 11:04pm
Either MJE243/MJE253 combination or BD137/BD138 - it's up to you, but only use one combination, not both in the same amp.

I meant by "correct" mounting was by following the diagram here:
http://www.diyforums.org/MiniMAX/MiniMAXbjt.php
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post #7 of 10
4/17/09 at 11:07pm
You need to choose one or the other. Refer to this Millett Hybrid MiniMAX BJT Transistors page of the MiniMax website to make sure you mount them on the correct side of the heatsink. The second set of holes is so you can easily use transistors with a reversed pinout.

If you are having trouble deciding which transistors to use there is a link on that same page to a review of the different transistors.
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post #8 of 10
4/18/09 at 10:49am
I think the guys have answered your question. However, to be perfectly clear (I hope), you must use only type of complementary transistor pair, and use one pair each for the Left and Right channel:

MJE243/MJE253 or
BD137/BD138 or
2SC3422/2SA1359, or etc., etc.

IOW, the final output of the amp/diamond buffer uses a complementary transistor pair in a "push-pull" arrangement.

So, if you've selected the MJE's, then you'd use one MJE243 per channel and one MJE253 per channel - that's all! Once you understand that, then the photo/diagram should make sense. It's a keyplan for where each of those go - with the understanding that only two sets of pairs of the same complementary, PNP-NPN transistor set are used. In the key plan below, only the transistors listed on the same lines in each drawing-note-leader are used for a particular build:
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post #9 of 10
12/14/11 at 9:42pm

Tomb, How noticeable a difference to you hear using the BD137/BD138  combination rather than the MJE243/MJE253 pairing. I always prefer a warmer sound, and I kno Steinchen reviews the  BD137/BD138 as being warmer with more bass, yet detail. Do you find any bad tradeoff for seeking this extra warmth, and is it in the Millet Hyrid Max a palpable difference?

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post #10 of 10
12/15/11 at 3:28pm
Quote:
Originally Posted by chadbang View Post

Tomb, How noticeable a difference to you hear using the BD137/BD138  combination rather than the MJE243/MJE253 pairing. I always prefer a warmer sound, and I kno Steinchen reviews the  BD137/BD138 as being warmer with more bass, yet detail. Do you find any bad tradeoff for seeking this extra warmth, and is it in the Millet Hyrid Max a palpable difference?


All I can say is that the BD137/138 is an extremely good transistor combination.  I still pack the toshiba 2SC3422/2SA1359's in the MiniMAX kits, but when they run out (Toshiba quit making them), the BD137/138 is what I will use as the replacement.

 

As for warmth and bass, you won't have an issue with that using almost any transistor combination on the MiniMAX - it's more an issue of the detail and overall dynamics that makes the difference in transistor sets. 
 

 

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