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Old 24th September 2003, 11:33 PM   #1
Pelle is offline Pelle  Sweden
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Default Q13 in Holton's n-channel amp

Hi,

can anyone explain to me why Anthony has put Q13 (IRF610 - Voltage amplification transistor) on the main heatsink?
Is it to help Q12 prevent thermal runaway when the sink is heating up, or is it just to keep it cool? According to my simulations approx. 1W gets dissipated in Q13, which should not be a problem to cool down without having to put it on the main heatsink.
The problem is that my PCB does not allow mounting Q13 directly onto the main heatsink, therefore i'm thinking of adding a small sink for the driver.

Comments on adding a separate heatsink for the voltage amplification transistor Q13 is very much appreciated.

Here is the schematic for the n-channel amp:
http://www.aussieamplifiers.com/down...nnel%20amp.pdf

Regards
Pelle
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Old 25th September 2003, 06:36 AM   #2
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According to the link, it's temperature
compensation,ie, it should be at the
same temp as the outputs for tracking.
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Old 25th September 2003, 01:12 PM   #3
mcp is offline mcp  United States
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Hi Pelle

You are right, Q13 need not be on the main heatsink. You can use small heatsink. But Q12 must be on main heatsink.
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Old 25th September 2003, 07:47 PM   #4
Pelle is offline Pelle  Sweden
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thylantyr,

you mean Q12, not Q13, right?

-Pelle
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Old 25th September 2003, 10:02 PM   #5
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Quote:
Originally posted by Pelle
thylantyr,

you mean Q12, not Q13, right?

-Pelle
yes,

my error.
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Old 25th September 2003, 10:39 PM   #6
jleaman is offline jleaman  Belgium
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Here is a few pictures of my n-channel right now. that i have..
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Old 25th September 2003, 10:40 PM   #7
jleaman is offline jleaman  Belgium
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Another.
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Old 25th September 2003, 10:42 PM   #8
jleaman is offline jleaman  Belgium
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Last one.
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Old 26th September 2003, 11:44 AM   #9
Pelle is offline Pelle  Sweden
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JasonL,
it looks like you have only placed the Q13 on the heatsink. If you have had problems with your amp blowing up or running hot then it's because you have not placed Q12 (where it says MJE340 on your pcb) ontop of one of the output-mosfets.

edit:
JasonL, I see that you have written Q13 beside the transistor that is Q12 in Anthony's new schematic. The designations may differ between his old and his new schematic.
But I still think you should move Your Q13 to the heatsink also.

-Pelle
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Old 26th September 2003, 05:21 PM   #10
jleaman is offline jleaman  Belgium
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HEY! maybe that is why my amp gets hot : O ) ill try that today then. So you all say that the one that is on the heat sink now doest have to be. well OMG ill change it and see.

i don't really use this amp much it sits in my closet.
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