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Pelle 24th September 2003 11:33 PM

Q13 in Holton's n-channel amp

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:


thylantyr 25th September 2003 06:36 AM

According to the link, it's temperature
compensation,ie, it should be at the
same temp as the outputs for tracking.

mcp 25th September 2003 01:12 PM

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.

Pelle 25th September 2003 07:47 PM


you mean Q12, not Q13, right?


thylantyr 25th September 2003 10:02 PM


Originally posted by Pelle

you mean Q12, not Q13, right?



my error.

jleaman 25th September 2003 10:39 PM

2 Attachment(s)
Here is a few pictures of my n-channel right now. that i have..

jleaman 25th September 2003 10:40 PM

2 Attachment(s)

jleaman 25th September 2003 10:42 PM

2 Attachment(s)
Last one.

Pelle 26th September 2003 11:44 AM

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.

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.


jleaman 26th September 2003 05:21 PM

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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