Pioneer SA-708 power transitors -help needed

1. You still have to find the fault that caused the outputs to blow in the first place. The bias trimmer tends to be a good place to start. These 12 A MT-200 transistors seem more than generously sized for a 65 wpc amp, more recent designs would have used 8-10 A TO-3P jobs.
2. I would never buy parts like this from random Chinese eBay sellers, you'll never know what you'll be getting. Stick with trusted distributors. I checked at Digikey - they have some 2SD2401 and 2SB1570 left in stock, those would be a good fit.
3. Use a bulb tester. You don't want your now-obsolete expensive replacement transistors going up in smoke right away.
 

BackZap

Member
2020-10-30 5:49 pm
Hi folks, sorry to dig up an old thread, buuuuuuuut...
What did you do to overcome the physical differences in the parts? The 2SD2401/2SB1570 packages are larger enough that the edges collide with the cut outs in the circuit board. It'd be possible to still mount the heat sink but it'll flex the whole main board ever so slightly. Alternatively I could raise the whole heat sink assembly up on about 2mm worth of washers and get the clearance I need.
I've never run into this problem before! Am I being over concerned about the flexing the board (and potential for heat transfer from the transistor package to the board) and is there anything wrong with using washers to raise heat sink as long as they are also a thermally conductive metal?
Any advice is appreciated!