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Old 1st April 2014, 12:27 PM   #101
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Quote:
Originally Posted by andresolomko View Post
On output I have only 13V of vdc with load
and (36!) with no load, so there is a huge voltage drop.
Hi, are you saying that you have 13V DC on the output when a load is connected and 36V DC when no load is connected ?
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Old 1st April 2014, 12:30 PM   #102
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Exactly. I suspect a BD640, since there is a strange voltage reading. 36 vdc on C and almost 0 on BE. If anyone sucseeded with circuit I need a reference voltages
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Old 1st April 2014, 12:52 PM   #103
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post your schematic, preferably with some test measurements appended.
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Old 1st April 2014, 02:01 PM   #104
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Default schematics

I am not sure how to do it but there is pdf All confusing measurments are with checkmarks
Attached Files
File Type: pdf apex 24 v pos.pdf (158.2 KB, 46 views)
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Old 1st April 2014, 03:00 PM   #105
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Check voltage across the three diodes and across the two 1uF caps.
Check the Vbe of the 4 output devices.
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Old 1st April 2014, 08:52 PM   #106
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Voltages on diodes are the same as supply (36vdc)
On fets are 12v
Same as output
I will test more but my main question: can this class A PSU work in a single-rail mode:
ie can I use only upper part of circuit? If it is so, so I have to debug it. Can be some problem on PCB or some faulty component.
If I feed it from unipolar bridge DC rectifier?
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Old 1st April 2014, 11:05 PM   #107
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Ok, my question is answered It was a bad 640 (strange, but it happens)
It can. Feeding from a ready made rectifier (+ to plus rail, - to ground) I can adjust voltage from 36 to 26,2vdc.
It's not a problem for me, since I use it for a mic pre. And extra 2v of headroom just make it beefy. So device with the same components values can regulate within 10v,as it was stated. Haven't noticed any heating problems so far, but ime will tell
And yes. Sound is much "tighter", comparing to LM*** -based PSU
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Old 5th April 2014, 07:20 PM   #108
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Default Help, please!

Pls anyone help!!!! It worked 1 day, suddenly R22 gave a smoke.
Also BC640. Replaced, the same story. Under load it gives like a half of supply voltage.
Voltages on 1u similar.
Trimmer don't help much. All problem is around BC640. I replaced few and all give a different result
Only one of 3 worked properly for a while before death.
Under normal working conditions collector of BC640 should give a half of output voltage.
i. e. when it was working normally I had about 12v on it and 25 on output, regarless of load.
As soon as I have a load it shows all weird things
Why the same place all the time? Anyone who is more experienced, tell me where to olook.
I am using MJE29/3050 since I can't get BD241/2 They are not direct replacement, but should work.
Can it be a reason.
Instead BC556 I am using 557, and BC549c instead of 50
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