Need Amp trouble shooting advise

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Reg18
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Need Amp trouble shooting advise

Post by Reg18 »

I've been having a little bit of trouble with a fuse popping on my new 5e3 amp.
It's a home build and the original owner/builder has been really helpful in trying to figure out what the problem might be but still having some issues.

It's the fuse beside the power chord (the amp has 2)
Played the amp for short periods over the first few days I had it with no issues at all.

First time the fuse popped was when I was trying out an attenuator with the amp,
Running the gain on both channels up high and the attenuator down low.
Popped the fuse almost immediately when turning up the gain on the amp (admittedly I used only one proper speaker cable and 1 guitar cable for the short 2 minute run through and the attenuator was set very low)
Second time I popped the fuse was under exactly the same circumstances but with 2 thick proper speaker cables as I thought that could be the problem.
Third time I popped he fuse was tonight running the amp at very low volumes (no attenuator used) and it was working fine but popped the fuse after an hour of the amp being on.

Which has confused me somewhat as it can't have been under any extra load at low volumes?

Anyone got any suggestions?
I could probably email a schematic with all the changes he has made from a stock 5e3 but can't seem to save them As images.

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Re: Need Amp trouble shooting advise

Post by sizzlingbadger »

Probably not going to get very far on here with help. It's the sort of issue that needs a meter and the amp on the bench in front of you.
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Re: Need Amp trouble shooting advise

Post by Bg »

Make sure you're using the correct fuses....
So, is that low alcohol or no alcohol at all? mmmm, no alcohol, do you want to try it? Noooooooooo.

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Re: Need Amp trouble shooting advise

Post by Molly »

Bad tube? Need for a slow-blow fuse?

Dunno, Reg. Maybe safest to get the local tech to look it over.

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Re: Need Amp trouble shooting advise

Post by sizzlingbadger »

Double check the fuse is slow blow and the correct value. Check the power tubes aren't red plating other than that you need to get a meter in there.
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Re: Need Amp trouble shooting advise

Post by Reg18 »

125Ma slow blow fuse which is his reccomended one.
His suggestion was to replace the power tubes and make sure they look symmetrical when glowing, run it for a while and see if it blows again. He is sending me another 5y3 rectifier tube to try as well.
Failing that he suggested checking inside to see if there is any visible arcing across Tube sockets.

Gonna try my spare set of 6v6s today and see how I go.

He's also happy for me to send it back for him to repair but he's just far enough away that I'd rather go to my local trusted tech tbh.

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Re: Need Amp trouble shooting advise

Post by JHorner »

Based on a number of second hand amps Ive seen, the popular solution to blowing fuses seems to be to put a 20A fuse where a 10A fuse is called for.

/Don't do this

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Re: Need Amp trouble shooting advise

Post by Bg »

Not sure why it has two fuses, the standard 5E3 only has the mains fuse which is a 2 amp slo-blow. If thats the mains fuse then its hopelessly under-rated. Try your spare tubes.
So, is that low alcohol or no alcohol at all? mmmm, no alcohol, do you want to try it? Noooooooooo.

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Re: Need Amp trouble shooting advise

Post by sizzlingbadger »

It may have an HT fuse too. 2A slow blow for the mains and 500mA fast blow for the HT would be good starting points.
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Re: Need Amp trouble shooting advise

Post by Bg »

sizzlingbadger wrote:It may have an HT fuse too. 2A slow blow for the mains and 500mA fast blow for the HT would be good starting points.
yeah just the whole 125ma slow blow thing? don't get it, as you say fast blow to save resistors if the tubes go... and its next to the power lead - guess that doesn't mean that much but I'd be checking its not the mains fuse.
So, is that low alcohol or no alcohol at all? mmmm, no alcohol, do you want to try it? Noooooooooo.

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Re: Need Amp trouble shooting advise

Post by Reg18 »

Bg wrote:
sizzlingbadger wrote:It may have an HT fuse too. 2A slow blow for the mains and 500mA fast blow for the HT would be good starting points.
yeah just the whole 125ma slow blow thing? don't get it, as you say fast blow to save resistors if the tubes go... and its next to the power lead - guess that doesn't mean that much but I'd be checking its not the mains fuse.
I don't know enough to figure out what's what, I was just going on the builders reccomendation. Never thought to ask why it had 2 fuses.
In other related news, changed the 2 6v6 tubes and been playing it off and on all day with no issues. Left it on for more than hour and played it again with no issues so fingers crossed it was just a dodgy power tube.

Edit: has just blown a fuse!

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Re: Need Amp trouble shooting advise

Post by Reg18 »

I've just sent the owner/builder a link to this thread in relation to the "what's the correct fuse" discussion.
Just an FYI
He's been very helpful even offering to replace the tranny if in fact it does come to that.

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Re: Need Amp trouble shooting advise

Post by Mini Forklift »

Reg18 wrote:Edit: has just blown a fuse!
FARK! :-(

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Re: Need Amp trouble shooting advise

Post by Reg18 »

So I've just changed the Fuse to a 250ma fast blow (don't get excited JB if you read this) and I think I must be going crazy but I swear it has changed the sound of the amp. It's quieter and the volume interaction is different. When in the bright channel if you turn up the normal volume before it added a lot of bass almost from 1 up but now it seems a lot more loner in response.
Edit: after changing back to the old power tubes I think the volume difference and channel interaction was due to the power tube change.

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Re: Need Amp trouble shooting advise

Post by calling card »

Check the rectofrier, valve or solid state?
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