June 18, 201313 yr Could change MJF15031 for MJE15031? I bought more transistors and I have four MJF15030 (lot: SPB16 - HFE=175,178,182,184) and 4 MJE15031 (I'm not sure of the manufacturer, lot: MA0 5K - HFE=180,185,190,190). Can I combine these MJF and MJE in this amp? -- o -- Rodrigo
June 18, 201313 yr Author sure as long as you use thermal isolation washers and in the one place isolate the two of them on the one bolt.
June 21, 201313 yr Author this is the original krell heatsink mouser 532-513102B25 Edited June 21, 201313 yr by kevin gilmore
June 21, 201313 yr So I'm the only one using the 2.5" sinks? They fit the chassis so why not... I got my panels back from the laser but the guy destroyed the front panel (don't ask). So I'll either have to use the back which is the suck in terms of finish or steal a fresh one from my stock and get a replacement sent with the next order.
June 21, 201313 yr Author I have the bigger heatsinks but one of the holes seems to limit The thermal efficiency. Will test... Would be nice if there was a taller heatsink with only one hole Edited June 21, 201313 yr by kevin gilmore
June 21, 201313 yr The mounting is not as nice, that for sure. One odd thing, I've ordered a lot of the larger 2.5" sinks and some have shown up with the cutouts while others have just had one mounting hole. Same Mouser number... Would be nice if there was a taller heatsink with only one hole *Calling Steve to the local Krell thread.... Steve to the Krell thread....*
June 22, 201313 yr Author so what we really want is avid part number 513202b02500g which is 2.0 inches high or 513302b02500g which is 2.5 inches high which is the to220 only version neither of which are stocked by digikey or mouser instock at Newark Edited June 22, 201313 yr by kevin gilmore
June 26, 201313 yr What is the current draw in each output transistor on the original unit? When I set it for 100mA, 1.5inch heatsink gets really hot.
June 26, 201313 yr The mounting is not as nice, that for sure. One odd thing, I've ordered a lot of the larger 2.5" sinks and some have shown up with the cutouts while others have just had one mounting hole. Same Mouser number... *Calling Steve to the local Krell thread.... Steve to the Krell thread....* Damn! Another missed opportunity.
June 26, 201313 yr Author What is the current draw in each output transistor on the original unit? When I set it for 100mA, 1.5inch heatsink gets really hot. its less than that, but I have that info at home. will look later. specific voltage across the emitter resistors.
June 26, 201313 yr Author That would work out to 2 watts per transistor, 8 watts, per channel. A bit too much, should be about 5 watts, about 1.25 watts per transistor. so about 125 mv.
June 26, 201313 yr Author ok, so the krell documentation is a little questionable, but when they measure the bias they do it from emitter to emitter. so the number is twice as big as the two test points I put on the board. specifically its 250 millivolts emitter to emitter cold, and 180 to 200mv hot. so at the two test points provided its 125 millivolts emitter to output no load cold a,d 90 to 100 millivolts hot. which sounds about right.
June 26, 201313 yr Thank you. When set Ic to 62.5mA@22V, surface temperature is down to 122F (50℃) Total current = +22V 400mA (with current to the Relays) / -22V 380mA
June 27, 201313 yr Mine is finish since a week, and when I start it, he smoke After some reseach, I found that the 500R ajustable was 500K !! Mouser make a little mistake ! I hope that with the good value, everything will be fine...
June 27, 201313 yr Thank you. When set Ic to 62.5mA@22V, surface temperature is down to 122F (50℃) Total current = +22V 400mA (with current to the Relays) / -22V 380mA How does it sound ? As good as expected from a Krell device !
June 27, 201313 yr Author Mine is finish since a week, and when I start it, he smoke After some reseach, I found that the 500R ajustable was 500K !! Mouser make a little mistake ! I hope that with the good value, everything will be fine... yep that is going to cause smoke.
June 27, 201313 yr yep that is going to cause smoke. I just hope that nothing else is broken... My PSU can give 300VA per side and there were in short cut !!
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