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Old 8th July 2013, 10:30 PM   #1
Champ is offline Champ  Canada
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Join Date: Sep 2011
Location: Toronto Ontario
Default Bob Latino ST120 Down

I have a Bob Latino ST120 (tubes4hifi amplifier KITs page) amplifier down for the count.
It all started with my Krell pre sending a surge of voltage into the amp. This is a KT88 based amp that is now blowing fuses. Sometimes the fuse blows right away and sometimes it will run for an hour then blow on shut down.

I have a measurement on the quad cap terminals of at least 6Mohms which I think would indicate that the power supply cap is good. The tubes all test good on my tester. I have gone through 2 rectifier tubes however. So the amp is blowing those eventually.

Is it an OPT? Perhaps one of the chokes. Any help as to where I should take it from here would be much appreciated.

Cheers.
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Old 8th July 2013, 10:44 PM   #2
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Join Date: Jan 2012
Location: Canada
Is the fuse between the power transformer and the wall? Maybe test what the power transformer is kicking out in terms of voltage (i.e. 750V transformer or 375-0-375). Also is the iron getting warmer than usual?

That is one huge chunk of iron on the Bob Latino amps.

Also, what did the amp sound like in that one hour of not blowing a fuse? Did you get stereo? Was it balanced? Some distortion that suddenly appeared where there wasn't any before?

Just asking because it might lead to someone else having better ideas than I have.
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Old 8th July 2013, 10:48 PM   #3
Champ is offline Champ  Canada
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Location: Toronto Ontario
Quote:
Originally Posted by overtheairbroadcast View Post
Is the fuse between the power transformer and the wall? Maybe test what the power transformer is kicking out in terms of voltage (i.e. 750V transformer or 375-0-375). Also is the iron getting warmer than usual?

That is one huge chunk of iron on the Bob Latino amps.

Also, what did the amp sound like in that one hour of not blowing a fuse? Did you get stereo? Was it balanced? Some distortion that suddenly appeared where there wasn't any before?

Just asking because it might lead to someone else having better ideas than I have.
Thanks overtheairbroadcast.

The fuse is right off the mains.
I do believe the transformers were getting hotter than usual.
The last time it played the amp sounded great. No distortion, had stereo as well. Just blew a fuse on shut down.
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