Blowing Fuses

[Sawgolf4me]

Hello Folks!

First time builder. First time poster. I finished putting together my Kaiju over the weekend. Fired it up Sunday night and everything was working great. Over the next two days, I probably listened 10 hours and turned it on maybe 5 times.

Well I get home from work today and I turn it on and I blow a fuse after listening for 30 minutes. So, I go to the store and get new ones. Now it blows fuses right when i turn it on.

So, I flip it over to inspect what is going on and don't see anything different. I am guessing the problem lies somewhere in one of my solder joints? My best guess is that warming up and cooling down a couple times caused one (or more) of the solder joints to break down? Any pointers on maybe where to start to look?

Thanks for the help!
Steve

 

[kgoss]

Go back through the resistance test again. That should identify the short blowing the fuse.
Are you sure you got the same value and fast or slow blow fuse that you had in the amp?

 

[Sawgolf4me]

I just looked and I bought 2 amp fast acting fuses. I’ll make a trip to an electronics store. To be honest, until about an hour ago when I searched fuses on here I thought all fuses acted as fast as possible.

I did the ground buss check on page 40. They were all at most 0.5 ohm. Is there another resistance check than that one?

Thanks for the help.

 

[Paul Birkeland]

Try a 3A fast blo fuse if that's all you can get.  Buy 5-10 of them, as there are a bunch of checks that can be done to figure out where in the circuit the issue is.

The first test is to pull all the tubes, then see if the amp fires up.  Let us know how that test goes.

You can also consider taking some build photos and posting them here, as we may be able to see something.

Also do be sure that the center lug of each hum pot isn't touching the chassis.

-PB

 

[Sawgolf4me]

I'm back in business! I found 1.6 amp time delay fuses. However, I'm still not sure what caused the fuse to go in the first place?

I ordered a BeePree, but it hasn't shipped yet. So I am listening from my MacBook Air straight to the Kaiju. I had some Jay-Z going at a pretty good volume. I'd bet the Kaiju around 80% volume. Can the fuse blow if you are listening too loud or pushing it too much?

Here are the checks I did today before I turned it back on.
1) I went through the Ground Buss check and everything measured 0.5 ohms or less.
2) Checked the rectifiers to make sure they were functioning and oriented correctly.
3) I visually checked that the center lug of each hum pot wasn't touching the chassis. I then did a continuity check and I got a buzz for a split second and then it went open line. Then I did a resistance measurement and they both measured almost exactly 1.00 kilo-ohm. Is that correct?
4) Then I turned it on without the tubes and it worked.
5) Then I put the tubes in and turned it on. Everything worked.
6) Then I did a music test and everything worked.

Pictures attached.

Thanks for the help!

 

[Sawgolf4me]

So literally as I hit send on that posting, the fuse blew again! I mean within 2 seconds of hitting post.

I was listening for maybe 10 minutes on low volume.

 

[Sawgolf4me]

I put a new fuse back in about a minute later and that one immediately blew when i turned it on.

 

[Sawgolf4me]

Ok. I think the only other datapoint I have to point out is that both of my tubes on the right side are dimmer than the left side.

I was doing some reading and clothes dryers seem to sometimes pop fuses after a period of time. And it is usually from the heater getting shorted to ground.

Thanks!

 

[fullheadofnothing]

I believe that time delay fuses are not the same as slow blow.

The fuse that shipped with your kit is a 2A slow blow. Some early kits shipped with 1.5A, but we were finding they would blow on first startup. As PB suggested, if all you can find is 3A, that's probably OK. His testing steps are going to be the way to find the problem; checking voltages could be helpful as well.

 

[Paul Birkeland]

I'd go with the 3A fuse and let us know if it holds.

Playing music really loudly won't make any difference.  The real stress on the fuse is when the amp is first turned on, as the power supply has to be charged up, and those 300B filaments draw significant current when they are cold.

-PB

 

[Sawgolf4me]

I put in a 3 amp slo blo fuse and turned it on with tubes in. Fuse blew immediately.

Then I tried with without tubes. 30 seconds later I had smoke coming out of the bottom of the transformer. So I turned it off. I had the plate face up at the time so I couldn't see what was smoking, but it was coming out of the bottom of the transformer. Not one of the open slots.

 

[Doc B]

Don't run it again until this is sorted out. That will only damage it more. You will need to test the rectifiers with a diode test to see if any are blown. Also look to see if you installed any filter capacitors backwards.

 

[Sawgolf4me]

Just did a test of the rectifiers and they all measure .635 volts.

I did a comparison of the capacitors to the final build picture at the end of the manual and they are all oriented the same.

 

[Sawgolf4me]

Top level shots

 

[Sawgolf4me]

Close in shots

 

[Alonzo]

In close up picture number 2, is the wire bridging the 220 caps touching the terminal strip ground tab (the one screwed to the chassis)?

 

[Paul Birkeland]

You'll have to very carefully run the tests on page 47.  You might want to use a pair of clip leads and power up the amp very briefly to get a look at those voltages.  Alonzo could be correct that you have half of a capacitor bank shorted to ground.  If things are getting hot enough to start smoking in the amp, this will alter the voltages a bit. 

It would also help to see a photo of where the UF4007s connect to the PT and terminal strip.

-PB

 

[Sawgolf4me]

Ok. I started it up one more time to try to measure the voltages and it immediately shorted (with a 3 amp fuse).

I added a couple pictures of the rectifiers and the caps.

Here is a recap of everything i've seen:
When I first built the unit, the power transformer was humming pretty good. I read on the forums that usually this is from the screws not being tight enough. So I tightened them down and then the humming went down quite a bit. This may or may not have been the day before the first fuse blew. I can't remember, but I tightened them before the fuse blew.

Then I blew the 1.6 amp fuse after listening for 30 minutes.

Then I put in a 3 amp fuse and the power transformer started smoking after 30 seconds.

Now I immediately burned a 3 amp fuse.

When I measure the resistances of the power transformer, I get these:
14-90 ohm
13-90 ohm
12-90 ohm
11-90 ohm
10-90 ohm
9-90 ohm
8-1 M ohm
7-1 M ohm

 

[Sawgolf4me]

Also, when I measure the power transformer mounting screws to ground, they measure 0.3 ohms. I thought maybe with the fabric washers, the power transformer was likely supposed to be isolated from ground?

 

[Adrian]

0.3 ohms is pretty small - could this be the normal resistance of your leads?