Simplistic Mosfet HV Shunt Regs - Page 368 - diyAudio
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Old 23rd December 2012, 09:41 AM   #3671
Salas is offline Salas  Greece
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Check Vbe for Q4,Q5 to make sure they still conduct and use another Q6. Also check its trimmer normally changes value with turning using DMM in KOhm when Q6 is out.
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Old 23rd December 2012, 10:52 AM   #3672
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I only have on hand at the moment 2 more Q4 (and/or Q5).....and 4 x Q6

What would be the best game plan that you would suggest that I should go forward B/4 I need to go shopping??
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Old 23rd December 2012, 10:54 AM   #3673
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May be you are thinkjing there are cold joints at Q4 &Q5??

I will check that first thing next.... tks...
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Old 23rd December 2012, 10:55 AM   #3674
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Pardon my poor English and/or typing....
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Old 23rd December 2012, 11:36 AM   #3675
Salas is offline Salas  Greece
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There is no plan by intuition. Measure that the transistors Q4,Q5 show healthy Vbe (0.6-0.7V) when the circuit is operating. If not, change. Change Q6 anyway, check trimmer.
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Old 23rd December 2012, 12:26 PM   #3676
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If change...Q4 / Q5 , change which one first (according to Salas' law..../experience)...(I will change Q4 N Q5...but which one first...)

I will change Q6 first....I have only 4 left...B/4 I need go shopping...

""Change Q6 anyway, check trimmer..."" do you mean, if after I change Q6...if not working...then I should change trimmer?? what do you want me to note when I check trimmer??

It is hard to check (or not much meaning to check again)....as they all checked out for the first hour...unless it is heat related.....

Do you think I should sink all Q4 & Q5 then...
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Old 23rd December 2012, 12:38 PM   #3677
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I have not sinked Q4 Q5 before when I use only one board (set at 50mA) to load both channels....

So I now think the problem is with the new board....Q6 then (Q4 and Q%...but in what order...)
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Old 23rd December 2012, 01:11 PM   #3678
Salas is offline Salas  Greece
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Use measurements. Normal overheat at that voltage output level is unlikely. Overbias due to a faulty transistor is more likely. Change Q4,5,6 if in doubt and the circuit is not in operational status handy to measure their Vbe. Trimmer should change value smoothly if you have a DMM on its outermost pins and turning its screw.
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Old 23rd December 2012, 01:20 PM   #3679
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Thankyou...will report back soon....Merry X'mas...
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Old 23rd December 2012, 02:32 PM   #3680
roger57 is offline roger57  Canada
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Quote:
Originally Posted by king4joy View Post
Thankyou...will report back soon....Merry X'mas...
Hi,

Not sure if you are using the small heat sinks on Q4 and Q5, if not, you might want to use them. I found it makes a huge difference. For example, even with the clip on sinks, the temperature still sits around 35 - 45C.

Merry Christmas
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