2. amps-preamps
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Fuses keep blowing

I have a Jolida 502a integrated amp, and it's worked perfectly fine for the last couple of years that I've owned it. Today, I turned it on, to let it warm up before playing some CDs and when I checked on it, "no power", checked the fuse and it was blown. Put another 6.3 Fast Blo fuse in, and powered the amp up again, Couple of minutes later that fuse had blown. So, I put another fuse in and guess what, that fuse blew. So I'm think something must be wrong with the amp, but I can't figure out what it might be. So, I'm asking you guys what y'all might thing it might be. Btw, I had a "tune up" on the amp about year ago and had some resistors and caps replaced, as the amp was approaching the ten year mark. Worse comes to worse, I might have to take a drive up to Annapolis and let the Jolida techs look at it.
cleaneduphippy
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almarg
9,670 posts
 
A couple of additional thoughts, beyond the (good) possibility that it is a shorted tube, or perhaps a failing capacitor:

1)Are the new fuses from Radio Shack, by any chance? If so, try some better quality fuses.

2)Are the connections to your speakers intact? If not (if one of the connections has been inadvertently dislodged) that could account for the problem, due to what is called "inductive kickback" from the output transformer, which occurs when a tube amp is operated unloaded.

Regards,
-- Al
marakanetz's avatar
marakanetz
5,473 posts
 
Very possible chain of tube events:
Shorted tube --> blown DC capacitor --> blown grid resistor.
cleaneduphippy OP
323 posts
 
Thank for the advice guys.

"Pull all tubes and turn it on. If that works, it could be a shorted tube-most likely an output tube"

Wouldn't it be better to just pull the tubes, and have them checked out on a tube tester? At least that way, I would know which tube was the "shorted" tube.

"1)Are the new fuses from Radio Shack, by any chance? If so, try some better quality fuses.

2)Are the connections to your speakers intact? If not (if one of the connections has been inadvertently dislodged) that could account for the problem, due to what is called "inductive kickback" from the output transformer, which occurs when a tube amp is operated unloaded."

As a matter of fact, yes, as it's the only place locally that I can find the 6.3 Fast Blo fuses. Also, the last fuse was a Radio Shack fuse and it lasted well over a year.

Btw, one of the first things I checked was all the connections, and they were all tight.

"blown DC capacitor --> blown grid resistor"

Think I'll check the tubes first, and if the problem still exist then I guess I'll being make a trip up to Annapolis to let the Jolida techs "under the hood".
andr
109 posts
 
I had a similar problem with a SS amp. It was overheating.

Installed it in a less enclosed place and that corrected the problem.
pescolar
128 posts
 
If all tubes works...check bias adjustment..maybe went to high after a while played.

Also if outputtubes read weak but still good to use ..adjust bias below bias maximum requirement.Just a thought.
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