kevin gilmore

krell ksa5 klone

621 posts in this topic

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

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sure as long as you use thermal isolation washers and in the one place isolate the two of them on the one bolt.

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Ok, many thanks Kevin.

Edited by PICaudio

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this is the original krell heatsink

 

mouser 532-513102B25

Edited by kevin gilmore

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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. 

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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 by kevin gilmore

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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....*  ;D

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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 by kevin gilmore
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Would these suit?

 

532-529902B25G  - 2 inch

532-530002B02500G - 2.5 inch

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Those are larger. The needed ones are thinner.

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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.

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I was wondering this as well. Seems like too much heat to get rid of.

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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....*  ;D

 

Damn! Another missed opportunity.

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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.

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It should be between 180-200mV if I remember correctly. 

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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.

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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.

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Ahh that explains it.  Bloody Krell...

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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

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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...

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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 !

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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.

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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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my guess is that the output transistors and the 2 ohm resistors are toast.

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