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/attachment.php?s=&postid=671676&stamp=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.
http://www.diyaudio.com/forums/attachment.php?s=&postid=671676&stamp=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.
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
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
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
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
Ok. Back with the fuses lol. Give me a few minutes and i`ll check out your suggestions. The fuse size is 3amp slow blow. Is this too small?
Steve.
P.S. here is the power supply.
http://www.diyaudio.com/forums/attachment.php?s=&postid=660174&stamp=1118349787
Steve.
P.S. here is the power supply.
http://www.diyaudio.com/forums/attachment.php?s=&postid=660174&stamp=1118349787
Do you smell anything after the fuse flows?
What is the va rating of the power transformer? Could be nothing more than the 3 amp slow blow fuse is not big enough. Inrush current to energize the transformer and charge the caps may be greater than 3 amps. Try a 5 amp slow blow fuse.
Another possibiltity is a shorted cap. Double check you have the polarity correct on the caps. You can use a simple ohm meter to check the caps for shorts.
Jim
What is the va rating of the power transformer? Could be nothing more than the 3 amp slow blow fuse is not big enough. Inrush current to energize the transformer and charge the caps may be greater than 3 amps. Try a 5 amp slow blow fuse.
Another possibiltity is a shorted cap. Double check you have the polarity correct on the caps. You can use a simple ohm meter to check the caps for shorts.
Jim
You are on the right track, but careful with the 514v, you may be exceeding the ratings of your caps. Don't want to create new problems fixing old ones.
Don't go 5A fuse. 3A should be plenty. I run 3A in my PP KT88 monoblocks.
A variac would have been helpful here, as would a current limiting lightbulb thingy. Maybe your next project?
It sounds like a hard short in B+ to chassis somewhere. Maybe some ohm checks from B+ points to chassis would be helpful. This doesn't require applying power.
Don't go 5A fuse. 3A should be plenty. I run 3A in my PP KT88 monoblocks.
A variac would have been helpful here, as would a current limiting lightbulb thingy. Maybe your next project?
It sounds like a hard short in B+ to chassis somewhere. Maybe some ohm checks from B+ points to chassis would be helpful. This doesn't require applying power.
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