Homemade Tube amp blowing fuses

[joecool85]

Can we have some pics of this amp?  It may or may not help us help you, but it will definitely be interesting to see!   

[sa230e]

Can we have some pics of this amp?  It may or may not help us help you, but it will definitely be interesting to see!   

Sure, here's a few pics I took when it was working. The matching speaker cabinet is also homemade. It has a single 12" Celestion Greenback in it.






I thought it turned out pretty nice for a first try. The inside, not so much. It's hard to do point-to-point wiring cleanly. Next time, I'm using turret board.



I designed the head to have a bottom plate so to work on it you just flip it upside down and take the plate off and you're in. You don't have to remove the chassis from the head.

[joecool85]

Wow! That's a looker! Great job!

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[sa230e]

Wow! That's a looker! Great job!

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Thank you. Much appreciated.

At this point since I guess I'm just going to do exactly what they tell you not do and put in a (slightly) bigger fuse and see what happens. I'm not sure what else I can do. Everything looks fine and a bigger fuse will probably solve the problem. Likely the inrush current is greater than I expected.

Still doesn't explain why it worked fine for 2 months on the 1A fuse, though which bothers me.

I'm gonna save up some money for a Variac and a decent analog multimeter.

[galaxiex]

Are you using SLO-BLO fuses?

Perhaps that would help.
I skimmed thru the thread and didn't see any mention of what type of fuse.
Sorry if I missed it.

My understanding is that SLO-BLO fuses are for exactly that, inrush current
yet still provide circuit protection at the given amp rating.

[sa230e]

Are you using SLO-BLO fuses?

Perhaps that would help.
I skimmed thru the thread and didn't see any mention of what type of fuse.
Sorry if I missed it.

My understanding is that SLO-BLO fuses are for exactly that, inrush current
yet still provide circuit protection at the given amp rating.

Yes, I have been using 1A slow-blow fuses.

[MasterVolume]

Hi i recently had hard to troubleshoot issues with an amp I had tweaked.

In the end I think it was solder shorting to ground one of the filter caps or dropping resistors.

After rebuilding bridge rectifier with new diodes on a tag board, the amps working great again.


good luck....


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[phatt]

I would try a 1.5Amp fuse and if that blows then back to looking for shorts in the supplies. Just don't throw in a 5 or 10 Amp fuse as that would be asking for a meltdown if something is shorting. As Master Volume just noted IF there is a short it could be hard to track down if it's a blob of solder or tiny bridging hair wire that is hiding.
Phil.

[sa230e]

So the new fuses came in. I popped a 1.25A slow-blow in and powered it up with the standby switch on to get the full in rush and it didn't blow. I played it for a while, it worked so I started playing with it, toggling the power off and on and then it blew.

So next I tried it with a 1.6A fuse and so far I haven't been able to blow the fuse. The amp works like it did. Nothing's getting hot.

I think I'm going to fiddle around with it a bit more until I call it "fixed".

Still bothers me that I can't figure out why it started drawing more current two months in.