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Old 3rd January 2013, 08:03 PM   #12751
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Default F5 psu

Hi there! I only got 22.7 vdc from the psu. Amplimo trafo 625va 2 x 18v, psu boards from Peter Daniels. Is the 22.7vdc enough to power the boards? I alaao paralleled the caps with filmcaps, 20uF, 2.2uF and 0.22uF. Could that be the couse of the drop of Vdc? Thanks for the answer, grtz Teake
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Old 3rd January 2013, 08:34 PM   #12752
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much more logical than getting 500Vdc , from 18Vac secondary

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Old 4th January 2013, 03:26 PM   #12753
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F5 DC at output.

Hi guys, wonder if you can help me. Finished f5 build, got it biased nicely and working well for half an hour playing music then I started getting 25v dc from speaker output. Burnt out test speaker. Now across resister 12 I get zero volts on both channels and on speaker output I now have 25 vdc on both.

I was able to bias only by adding two additional 2.2k resistors across r4 on both channels. INitially, When I adjusted the amp warm, I got .59 v across r 12 and r 11 on both channels, but when the amp cooled off, this figure went up to .90 v on both channels, but as the amp warmed up, it went down to the .59 v figure. Is this difference in voltage between a warm amp and a cold amp normal?

Currently, I am getting zero v across resistor 12 and 11 on both channels and 25 volts on both speaker outputs.

Any ideas what could have blown. I looked carefully, resoldered all suspected joints, and nothing looks burnt or damaged on the sight.

Where would you suggest I look?
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Old 4th January 2013, 03:42 PM   #12754
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desolder Jfets and mosfets from circuit , test them
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Old 4th January 2013, 03:45 PM   #12755
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do you have one PSU for the whole amp? or one pr ch?
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Old 4th January 2013, 03:47 PM   #12756
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You have ground the PSU connected on both channels?

May be that the ZTX spoiled ...

Until you get to the problem I measured all R.

Confirm the R11 and R12 measure 0.47 ohm?

Confirm the R17 and R18 1K measure?
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Old 4th January 2013, 04:28 PM   #12757
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Thanks, one power supply for whole amp, grounded to both channels build following Nelson's F5 pdf writeup.

R11 and 12 .47 ohm checked, and r17 and 18 will check to make sure 1k.

If one Fet problematic would this make DC 25 volts at both channels? Thanks and will try to remove and test if I can get them out without ruining.
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Old 4th January 2013, 04:50 PM   #12758
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In both channels think hard ...

Must see before all the tension that comes from the source, there may be the problem ...
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Old 4th January 2013, 04:57 PM   #12759
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Quote:
Originally Posted by JohnGeneva View Post
Thanks, one power supply for whole amp, grounded to both channels build following Nelson's F5 pdf writeup.

R11 and 12 .47 ohm checked, and r17 and 18 will check to make sure 1k.

If one Fet problematic would this make DC 25 volts at both channels? Thanks and will try to remove and test if I can get them out without ruining.
make sure your PSU works as it should. i suspect a bad connection on the negativ rail.
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Old 4th January 2013, 11:04 PM   #12760
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Yes, I think my problem was power supply... which may have caused other damage. power supply on positive rail was fine, but on negative rail was zero. 18 v transformer and one rectifier bridge does not appear to be working and was getting very hot. to test I disconnected capicitor bank and then tested for dc from bridge... when I tested negative rectifier bridge on negative rail it measured 36v for a few moments then to zero on the negative rail so looks intermitten and then positive rectifier gave me 36v.

I believe I made an error in the power supply which manifested itself... I mistakenly hooked positive from the bridge rectifier to negative on the capacitor bank. I attach a pdf of power supply diagram I used, just to make sure this is correct, positive from the bridge rectifier goes to positive side of capicitors on both positive as well as negative cap bank as per this attached pdf. Does this pdf appear to be correct?

Will sort this out tommorrow and see if power supply hooked up properly fixes it, or will I have blown out some of the fets....funny however, it worked with this error for about half an hour.
Attached Files
File Type: pdf power supply f5.pdf (37.4 KB, 90 views)
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