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Old 25th June 2006, 06:19 PM   #1
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Default Troubleshooting.

What`s the best way to approach troubleshooting a newly built amp that blows the fuse consistantly on startup? I`ve checked the power trans with secondaries disconnected and voltages are ok. Here is the circuit.

http://www.diyaudio.com/forums/attac...amp=1119993206

Power supply is 5u4-40uf-10h-100uf. Please give me some pointers to check out. I`m pretty new to this but have built a couple of things so far with no trouble.
The fuse is blowing with only the rectifier in place.
Thanks, steve.
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Old 25th June 2006, 06:26 PM   #2
poobah is offline poobah  United States
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In your situation... divide and conquer.

Can you post the PSU as well?

1) What size is your fuse?

2) Disconnect the B+ between your PSU and the amp... in other words unload the supply. Does that fix it? if so the problem is in your amp and not the PSU.

3) If not the problem is in the PSU. Rechec your wiring and post

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Old 25th June 2006, 06:36 PM   #3
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Quote:
Power supply is 5u4-40uf-10h-100uf.
Isn't 40mfd kinda high for the input cap? I thought it should be around 4mfd. Check connections on rectifier tube.
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Old 25th June 2006, 06:48 PM   #4
poobah is offline poobah  United States
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Good point Joe,

40 uF seems to be max for that tube...

You know... if it's popping the fuse RIGHT NOW, maybe it is something as simple as heater wiring?

I mean a PSU should at least take a couple of seconds to show itself.

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Old 25th June 2006, 06:51 PM   #5
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What if you pull the rectifier tube? As stated it was run without tubes. That left the rectifier tube, the 5 volt heater winding and a 6.3 volt heater for the 6N1P and KT88 in circuit.
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Old 25th June 2006, 07:05 PM   #6
poobah is offline poobah  United States
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Hmmm... check heater wiring...
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Old 25th June 2006, 07:06 PM   #7
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Could be a short in the transformer.
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Old 25th June 2006, 07:08 PM   #8
poobah is offline poobah  United States
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Castle... are you there?
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Old 25th June 2006, 07:37 PM   #9
moamps is offline moamps  Croatia
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Hi Steve:

1. Pull out all tubes. Connect the secondaries of the transformer to the circuit. Turn the power on. If the fuse doesn't blow, check all heater voltages on the tubes' sockets, and check HV voltage on the rectifier tube. If the fuse blows, it means the fuse is too small or you have one or more shorts in your circuit. Disconnect the secondaries from the circuit one by one to find out which one makes the short.

2. If the fuse hasn't blown and you have checked all AC voltages on the tubes sockets, disconnect the HV secondary and put back all the tubes taking care that the power is off. When you've done that, turn the power back on. If the fuse doesn't blow, check heater voltages on all tubes and see if the tubes warm up. If the fuse blows, the fuse is either too small or you have a short in one of the tubes. Remove the tubes one by one to find out which one has the short.

3. If the fuse didn't blow in steps 1 and 2 and you still haven't traced the problem, reconnect the HV secondary and disconnect the second LC filter (while the power is off). Turn the power on. If the fuse doesn't blow, check the voltage on the first rectifier cap. If the fuse blows, check the rectifier tube and the first rectifier cap.

There are more troubleshooting steps but I've omitted them here because, if I understood things correctly, the fuse blows as soon as the power is turned on so these 3 steps should be enough to find the culprit.

Regards,
Milan
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Old 25th June 2006, 07:42 PM   #10
poobah is offline poobah  United States
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I bet Castle ran to the store to buy fuses...
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