Q13 in Holton's n-channel amp - Page 2 - diyAudio
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Old 27th September 2003, 03:36 PM   #11
Pelle is offline Pelle  Sweden
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JasonL,

try adding the Q12 to the top of one of the mosfet's, best on top of the mosfet that draws the most current.
But leave Q13 on the main heatsink since it needs to be cooled down.

Post your comments here after you've tried it.

-Pelle

Edit:
I still need to know if it's totally OK to mount Q13 on an external heatsink.
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Old 1st October 2003, 12:51 AM   #12
jleaman is offline jleaman  Belgium
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Pelle well i did what you said and well heh my amplifier no longer works now. Not blaming you just want to solve the problem .

i powered it up no smoke no bangs or any thing not even any heat. Cool but when iwent to put a speaker up to it. POP the speaker almost blew.. so i used my dmm and found out that there is a raw 74.5vdc ( te rail voltage. ) on the out put.. Any clue to why this is happening. : O) ..? Good thing i didn't sell it id feel bad to the person that took it home.
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Old 1st October 2003, 07:40 AM   #13
Vigier is offline Vigier  Netherlands
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Jason,

1) are you ABSOLUTELY sure that the transistor you mounted on the heatsink is isolated from the heatsink?
2) since you probably use wires now to connect the transistor: nothing that touches some other metal?
3) are you sure you attached the wires the right way? mayby rotated 180 degrees?

Grtz, Joris

P.S. Are you sure your speaker is still working? Not so many speakers that can handle 74.5 Vdc!
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Old 2nd October 2003, 02:10 AM   #14
jleaman is offline jleaman  Belgium
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yeah i checked the speaker it is still alive, and running well. But i just cant figure out why it is pumping the rail voltage through the speaker. i looked at it with my dmm and it is a - voltage not a positive. i looked at the pads no ware marks no metal shavings under or near the fets either. and yes i had the polarity properly.
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Old 2nd October 2003, 02:25 AM   #15
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Default Is the picture correct.

I might be making a mistake but I think the transistor is connected wrong. If you look at the transisor in the picture from the ceramic resistor end , base is on the left.
The transistor has physically the same orientation when mounted under the board on the heat sink. So left terminal goes to base on board etc. But it "look" like the leads have been reversed except for the middle one!
Am I wrong ?
Cheers,
Ashok.
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Old 2nd October 2003, 03:03 AM   #16
jleaman is offline jleaman  Belgium
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Well in them previous pictures the amplifier ran perfectly and strong. O ) but now it just outputs voltage into the speaker output. BUT. when it was in storage it might have gotten bumped or something. i checked all the solder joints and they all seemed find. i guess i should have powered it up before i did this




Humm no idea what to start with now either.
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Old 3rd October 2003, 07:51 AM   #17
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Default Look carefully.

Hey Jason look at the TO220 transistor under the board. If it is the same one that was above the board , you have INVERTED the leads !! It should not be as the transistor is oriented the SAME way!
Cheers.
Ashok
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Old 3rd October 2003, 09:44 AM   #18
Cobra2 is offline Cobra2  Norway
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Default My N-Ch.....

Works perfect! (See picture).
(NB! Resistors are on reverse side...)
Arne K
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File Type: jpg n-ch-ak1.jpg (67.5 KB, 171 views)
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Old 3rd October 2003, 05:51 PM   #19
jleaman is offline jleaman  Belgium
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here is the board before it worked. : O ) and it is the same way still BUT not working : O )







http://24.71.244.254/Photo/view_phot...15&id=DSCF0029
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Old 4th October 2003, 12:45 PM   #20
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Default I got it wrong.

Yes this picture shows it clearly. I got the orientation wrong from the close up picture. Any possibility of the insulation between the transistor and heat sink being faulty ?
Cheers.

Something wrong here. In the picture in your earlier post the transistor seems to be facing the wirewounds and the edge of the board. In the current picture the transistor is facing into the board. If both are identical , I must be really getting mixed up.
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