I cannot see a break, but it looks like it took a shot. Does anyone think this might be a problem, or at least what is causing my hum?




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What he said ^^^

With fuses there is no downside to replacing one you think might be a problem. Even if you can't see anything obvious.

Did you replace the rectifier? If not I would strongly recommend you do that too, otherwise you're likely to blow one or more fuses again and sooner rather than later.

Just FWIW, if you haven't considered NOS here is a link to a discussion about buying NOS rectifiers, which many of us think are superior to average current production. Also Steve's thoughts on the subject:

https://www.decware.com/cgi-bin/yabb22/YaBB.pl?num=1605822949

I believe it happened when I popped-in my 1960 RCA 5R4.

I certainly was impressed with the wiring under the hood. I was able to confirm I got the Miflex cap upgrade back in April 21.

Like the others have said…. definitely replace the fuse and see if by swapping out the rectifier that the hum goes away.  

Just the other day I noticed that my SE84C+ 25th amp has developed a hum.  I was originally running a Raytheon 5Z3 rectifier, so tomorrow I’m going to pop in the original stock PSvane 5U4G rectifier and stock fuse that came with the amp as part of my warranty transfer.  
I’m hoping that my SR orange fuse that’s currently in the amp isn’t compromised….but thankfully I have a backup Orange for moments like these.  To the OP…. Keep us posted on what the cause was.   I’ll do the same.

Dom

James…. I put the orange fuse at the main receptacle.  I knew if that fuse blew I wouldn’t get any sound…just wanted to cover all bases with swapping things out in trying to narrow it down. So far nothing.  The Raytheon rectifier is fine.  Heck I even swapped out amps and speakers and the hum is still there.  

Next I’m going to try and individually pull components from the signal chain and then swap out my ZSTAGE and ZROCK2 tubes. I’ve already checked to make sure I have no ground loops from the power and audio cables coming in contact with each other.  Since I’m getting hum with the Torii and Zen amp connected,  don’t think it’s the amp.  I’m guessing maybe a tube from the ZSTAGE or the ZROCK2.  After that I’ll start swapping out audio cables and then power cables.  

I only hear the hum when I put my ear close to the speaker grill…. So maybe it’s just low level hum that my system is producing but lots more to tinker with.  

Thanks for the info.

Dom

In my experience with my amps that have the fuse board under the chassis there are 5A fuses in that spot for the rectifier.

I don't have your eyes, can't say what you are seeing. But I do remember reading about 500 ma fuses and perhaps in some components that is correct. It's rather confusing and there is not a lot of straight-from-the-horse's mouth information easy to find.

Fuses can easily be confused and installed incorrectly. I've done that several times myself.

Steve just emailed me and said they were putting 500 mA fuses in the UFO2, and now they recommend the 200 mA. He mentioned the manual is incorrect. And yes, calling Decware is a good idea. I will when I get the chance.

Thanks for all of your responses, gentlemen.

I am good to go. Sorry if my answer earlier sounded abrupt, but I was leaving for work.

I ordered what I need, and when I take it apart tomorrow, I will take note of everything in each position. I have some 500 mA fuses on the way. I will replace what I have just to see if the hum goes away. I have yet to replace the rectifier, so it may happen again.

I will report back tomorrow with my result. Thanks to all. You all have been a great source of knowledge.

-Danny

Yes, he did recommend the 200 mA fuses, and I plan to change to those. I am thinking the same thing for the rectifier. I will be replacing it soon, or it will just go on it's own.

Glad you are back in business!

In general those flashes are not good signs for tube health. Sometimes hundreds of hours may still be available. Sometimes very few. Extra fuses and back up rectiifers are good to have.

Thank you, thank you. That was my thought as well. I still have the hum, but I believe the rectifier could have damaged the new fuse. I know, I know, that rectifier in question will be replaced. I'm not in the mood to pop the hood again to look at it. I will wait until I receive my new rectifier.

When I looked at every fuse in my amp, I found a ceramic 6A (slow or fast-blow unknown), and 2-500 mA slow-blow glass fuses under the rectifier. At the plug, I found a 3.15A fast-blow glass fuse. Again, Steve emailed and said the 500 mA fuses are no longer installed, as they have changed to 200 mA fuses for their current production. He also mentioned the manual has not been updated.

On a funny note, you should see me walk across the house carrying the amp in order to pop the top. My wife said I looks like I'm carrying a bomb that is about to go off. Ha.  

Speaking of hum…I went crazy for the past two days trying to isolate transformer hum on my Dennis Had amp. It was audible from 10 ft.

At first I thought it was a faulty power cable—tried 3 different cords—nope — if anything it got worse with the stock PC.
Then I thought it might be my beloved Sophia Aqua 274B rectifier (sweating bullets at this point). But nope—Dropped in a GE 5U4 and the same issue.
Then I thought to change out my 6SN7 input tube and voila—-the hum dropped to almost negligible levels—normalcy restored.

Didn’t realize a bad input tube (or going bad) could cause really audible transformer hum.

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A lot of times what happens is the filament gets loose and the AC heater current cause it to vibrate. The causes the hum.