# 6G16 Vibroverb - blowing fuses



## Lincoln (Jun 2, 2008)

A brown-face vibroverb I built a year or so ago. It's been randomly blowing the fuse, about 6 times in the last year. I've narrowed it down to knowing it only happens when the tremolo is being used. Everything works normally. Any insight or clues or suggestions as to where I should be looking and what I should be looking at? I really don't have anything to measure current flow. No drastic voltage drops anywhere I can find. 

????????


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## epis (Feb 25, 2012)

Check out the bias. Bias wiggle tremolo should be adjusted on the cold side.


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## Paul Running (Apr 12, 2020)

What current trip value and type...fast or slow blow?


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## Lincoln (Jun 2, 2008)

mostly AGC3's, last one I blew was an AGC4

(normal automotive type fuses, not slow blow)


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## Lincoln (Jun 2, 2008)

epis said:


> Check out the bias. Bias wiggle tremolo should be adjusted on the cold side.


I can't remember where I set it, but knowing me, it's on the high limit.  I'll check it


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## jb welder (Sep 14, 2010)

The bias runs through the wiper contact of the intensity pot. Any oxidization or glitchiness in that wiper contact means bias is lost and power tubes run flat out, probably blowing the fuse.


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## Lincoln (Jun 2, 2008)

epis said:


> Check out the bias. Bias wiggle tremolo should be adjusted on the cold side.


I wasn't as high as I thought I was. It was set to 34mv @ 450V on the plates. Less than 60%, right? I backed it off to 20mv @465V, I'll see if that makes a difference.


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## Paul Running (Apr 12, 2020)

Paul Running said:


> What current trip value and type...fast or slow blow?





Lincoln said:


> mostly AGC3's, last one I blew was an AGC4
> 
> (normal automotive type fuses, not slow blow)


Hi, if you have a Kill-a-Watt, you could monitor the real-time current or power consumption, to verify consumption at the mains.


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## Lincoln (Jun 2, 2008)

I had to Google "kill-a-watt", but I'm glad I did. Looks very useful and affordable. I "need" something like that. 

Amazon.ca to the rescue!


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## Lincoln (Jun 2, 2008)

jb welder said:


> The bias runs through the wiper contact of the intensity pot. Any oxidization or glitchiness in that wiper contact means bias is lost and power tubes run flat out, probably blowing the fuse.


with the assistance of a large, lighted magnifying glass.....I found a single strand of a multi strand wire, hanging out and making contact between the wiper post and an element post. Fixed that and I've been playing on full tremolo intensity for quite a while without blowing a fuse. You may have nailed it on the head, yet again. The sweep of the pot was real nice in both directions btw.

A "thank you" goes out to you all.


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## Paul Running (Apr 12, 2020)

Lincoln said:


> with the assistance of a large, lighted magnifying glass.....I found a single strand of a multi strand wire, hanging out and making contact between the wiper post and an element post. Fixed that and I've been playing on full tremolo intensity for quite a while without blowing a fuse. You may have nailed it on the head, yet again. The sweep of the pot was real nice in both directions btw.
> 
> A "thank you" goes out to you all.


That's another great tool for troubleshooting...many faults can be detected with a good set of eyes, light and magnification...good show.


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## Latole (Aug 11, 2020)

epis said:


> Check out the bias. Bias wiggle tremolo should be adjusted on the cold side.


I agree, bias could be too hot.


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## Lincoln (Jun 2, 2008)

I got my power usage meter this morning. This amp is drawing 40 watts until the tubes come up, then it increases to 72 watts. Tremolo on max, it draws 80 watts of power.

I have a foolish need to short out those two posts on the trem intensity and see what that does to the draw. I'm semi-fighting this urge. I'll keep you posted.


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## Latole (Aug 11, 2020)

It is tubes dissipation ?


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## Lincoln (Jun 2, 2008)

No, that's the current to the primary side of the power transformer. The A/C 110V plug in. If I tweak the bias right up to 40mV, I can get it up to 90 watts of primary current, but that's it.
Not enough to blow a fuse.


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## Latole (Aug 11, 2020)

Remove all tubes, Power amp ON and see if fuse blow.
Fuse blow; issue in power supply 

To save fuse and to work easily in the amp, build ans use bulb lamp current limiter.


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## Latole (Aug 11, 2020)

" A brown-face vibroverb I built a year or so ago. It's been randomly blowing the fuse, about 6 times in the last year. I've narrowed it down to knowing it only happens when the tremolo is being used."
-Lincoln

IMO something you do wrong, bias too hot or ....? 
You may think your work is right but is wrong.


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## jb welder (Sep 14, 2010)

Latole said:


> IMO something you do wrong, bias too hot or ....?
> You may think your work is right but is wrong.


Latole, he fixed the problem in post #10 above. A bit of wire was stuck in the tremolo intensity pot and messing up the bias (probably shorting it to ground).



Lincoln said:


> with the assistance of a large, lighted magnifying glass.....I found a single strand of a multi strand wire, hanging out and making contact between the wiper post and an element post. Fixed that and I've been playing on full tremolo intensity for quite a while without blowing a fuse.


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## Latole (Aug 11, 2020)

jb welder said:


> Latole, he fixed the problem in post #10 above. A bit of wire was stuck in the tremolo intensity pot and messing up the bias (probably shorting it to ground).



Why the title of this post ??
*6G16 Vibroverb - blowing fuses*


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## Verne (Dec 29, 2018)

He titled the post before the cause was found and fixed. It's common to do that. That is why the name of the post is such.


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## Latole (Aug 11, 2020)

Thank you.
He Can't edit title ; 6G16 Vibroverb - blowing fuses ; Fixed


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