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Symmetrical amplifier conundrum
Symmetrical amplifier conundrum
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Old 29th January 2003, 11:52 PM   #21
Kilentra is offline Kilentra  United States
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Default Bolting through

Hm, okay, thanks for the tip... it does appear the hole on the BD139 is not quite large enough for the screw I have to use ("#6-32"... silly American measuring system ), but it is a small enough discrepancy that I'll just drill out the difference and see if it still works. I recall seeing that transistor dies are placed close to the center pin inside the casing, so I think it will go OK.

If this doesnt work, I will just mount Q10 on the aluminum bracket, adjacent to the output stage (on the side of the bracket bolted to the heatsink).

I don't know for sure if mounting through a bolt is a better choice than mounting directly to the same heatsink. I would think using the common bolt would be better, since the bolt tends to also conduct heat ... the BD139 case would be in direct contact with the Mosfet's case both through the bolt (and washer maybe), and because it would be squished down on top of the case. (I'll use thermal paste, there shouldn't be a problem with electrical continuity). The parts are in the mail, I will let you know how it goes.
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Old 31st January 2003, 04:56 AM   #22
johnthetweeker is offline johnthetweeker  India
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Originally posted by Kilentra
Hi, I have one last question.

How am I supposed to mount Q10, the Vbe multiplier device, on top of the output stage Mosfets?

Is it really necessary to mount the Vbe device ON the output device? I don't know about MOSFETs, but in a bipolar darlington amplifier (using 2N6059/6052 at the output) I had mounted the Vbe transistor right next to (almost touching) one of the output transistors, and found the sound degraded (difficult to describe, but some kinda slow ramp-like effect). I assumed the reason to be thermal overcompensation, and moved it away; the problem got solved.

I wonder if anyone who built this amp tried mounting the Vbe transistor on the heat-sink and not directly on the output device?

John (not the baptist)
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Old 31st January 2003, 05:06 AM   #23
jleaman is offline jleaman  Belgium
Join Date: Apr 2002
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if your still wondering how you should mount that transister. that changes the bios/over heat desapation. I mounted mine in the middle. It seems to be ok. I to have emaild anthony but still no reply's at all. im kinda concernd now because i just bought 2 av800 boards for my audio system to run my subwoofers. I dont think ill have any problems but hey he could email me back and answer my questions.
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