what to build with these

You could build a Mother of a sub amp (mono) or a 2 channel amp with 4 pairs/channel. These MJ15023/4 have good beta holdup to about 2-3A , so there's 8-12A per channel. Also their SOA at 80V is on 2A which derates the case thermal limit to 160W - a good margin. So if your after an 8 ohm amp you're set. Just need some good drivers. I used to use 2N3584/6421 both TO66 for this purpose and they should easily drive 4 pair. I would use a cfp with 5551/5401 for driver and predriver. Then a LED feedback complementary cascode Vas and dual diff'l input either fet or bjt.

Too easy.
 
heard and read lots good things about the leach amps might look into it what the complexity of the build like for the leach amps? .just a heads up all these components are recovered from a dead peavey 8.5c all output transistors desoldered and tested ok. unfortunately the drive stage detonated its transistors .

couldnt capture the blue smoke and save the soul of that amp :hot: :bawling: :hot:
 
will go with the leach.I will be arranging the ordering and the delivery of the components in the next 2 weeks. is there anything else that you guys think i will need to take into account for the uprating of this design(aside from a bigger heatsink :hot: ). will also be mounting the ouput transistors in a fan type HS(pic attached) facing each other in a tunnel ram style .
running on the presumption the leach isnt a DIY amp/heating system:hot: :hot: .:confused:
 

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In case you missed it, there is a Leach board group buy going on now. http://www.diyaudio.com/wiki/index.php?page=+Leach+Amp+PCB+Group+Buy this board is a Jens Rasmussen redesign for Plastic output devices. http://www.diyaudio.com/forums/showthread.php?s=&postid=658070#post658070 for info

Contact Gengis immediately if you are interested, as he is taking money right now, planning to order on Friday.

Edit:

No, the Leach does not waste a lot of heat. I've got a 4 channel version on one of Apex Jr.'s tunnel heatsinks (about middle of this page http://www.apexjr.com/new.htm - easier to use than the sinks you show for TO-3 devices) that does not need a fan for most home use. It sounds very nice.