My MCi keeps blowing fuses

  • Thread starter Thread starter Slowner
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Slowner

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Any idea why? Could it possibly be the power tubes? Does this amp have a rectifier tube and if so, is that a possibility?
thanks
 
Probably a power tube, none of the Wizard amplifiers have a rectifier tube.
My Metropoulos DVL was doing the same thing, blew a fuse a couple times in a row and I put a fresh set of 34s in it and it’s purred like a (MONSTER) kitten ever since.
 
Yeah, I'd go first for the Power tubes as the likely cause.
I had similar on my SS100 recently as it started blowing fuses. All the tubes all lit up fine, no visibly dead tubes either unlit or red plating. Swapped out the full set and she's good to go again. I found out which one it was and now have 3 emergency spares on the shelf.
 
Excuse my ignorance but can I just swap,out one tube, assuming I find out which one it is, or do I need to replace the whole set?
 
Short answer, yes…

Long answer, is it a tube that is matched to the set that’s in there?
Are you sure which tube it is?
You could keep blowing fuses until you find the right one.
And then, when you do find the right one, maybe the tube that you put in, (unless it is matched to the other ones), will red plate etc. etc.

So, yes, if you know the bad culprit, you can replace it with another one as long as its at least within bias range to the tubes which are already in there, or at least somewhere ‘remotely close’ range…

I’ve replaced one tube at a show and it was way way on the cold side, when I checked the next day in the morning, it was only pulling 17 mA where is the other ones were at 35 mA but as long as the one you put in as colder and not way too hot, at least you’ll be safe, maybe not the optimum tone however, but ‘safe’.

Edit… I have a few friends that do not like closely matched quads in their amplifiers, they prefer hotter ones in the outside sockets and the cooler ones on the inside and they seem to feel they get a more full range tone…
I guess it’s all subjective.
I have never tried this method, I have always just used matched quads, but it would be interesting to try someday. Who knows, depending on the amplifier, Maybe they’re right.🤔
 
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Be happy the fuses are blowing. I would cease before you have major issues. Replace power tubes asap. Matched set.
 
SQUAREHEAD said:
Short answer, yes…

Long answer, is it a tube that is matched to the set that’s in there?
Are you sure which tube it is?
You could keep blowing fuses until you find the right one.
And then, when you do find the right one, maybe the tube that you put in, (unless it is matched to the other ones), will red plate etc. etc.

So, yes, if you know the bad culprit, you can replace it with another one as long as its at least within bias range to the tubes which are already in there, or at least somewhere ‘remotely close’ range…

I’ve replaced one tube at a show and it was way way on the cold side, when I checked the next day in the morning, it was only pulling 17 mA where is the other ones were at 35 mA but as long as the one you put in as colder and not way too hot, at least you’ll be safe, maybe not the optimum tone however, but ‘safe’.

Edit… I have a few friends that do not like closely matched quads in their amplifiers, they prefer hotter ones in the outside sockets and the cooler ones on the inside and they seem to feel they get a more full range tone…
I guess it’s all subjective.
I have never tried this method, I have always just used matched quads, but it would be interesting to try someday. Who knows, depending on the amplifier, Maybe they’re right.🤔
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The OT sees two tubes in a pair as one, as each OT leg is on one pair of tubes. The sum of those two tubes for current draw is what the OT sees. I match my tubes into two pairs. Usually a hotter one in the outside and cooler on the inside but it doesn't matter if it's vice versa. Take all four tubes and put the highest testing tube for current draw with the lowest one for one pair.
 
So, I replaced the power tubes with a matched quad and the left tube blew As well as the 4 amp fuse. Looked at the old tubes I took out and one of those was blown, same spot as the one I replaced that blew.
im lost. Off to an amp tech.
 
Slowner said:
So, I replaced the power tubes with a matched quad and the left tube blew As well as the 4 amp fuse. Looked at the old tubes I took out and one of those was blown, same spot as the one I replaced that blew.
im lost. Off to an amp tech
Click to expand...
I assume you checked the bias? Being that you blew the fuse more than once you probably had a bad tube initially. Now you probably have one or two open screen resistors. You can measure them easy enough with a multi meter. If you did not check the bias then you're better off with a tech
 
Thanks Glip. Yeah I think this is beyond my scope (pun intended). Now to find a tech…
 
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