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 Post subject: Curtis Mathes Fuse?
PostPosted: Sep Sun 05, 2021 9:31 pm 
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Location: Simi Valley, CA
Hello,

I am working on a Curtis Mathes tube amp/tuner and the separate mains trans has a wire fuse which I think would be good to replace with a glass one....what do you think the rating of the new fuse should be?

Thanks.


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 Post subject: Re: Curtis Mathes Fuse?
PostPosted: Sep Sun 05, 2021 9:49 pm 
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Joined: Nov Tue 14, 2017 5:09 am
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Location: Austin, Texas
That looks like a 6.3VAC winding. I think the #26 wire is a good choice for the fuse.

Jay


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 Post subject: Re: Curtis Mathes Fuse?
PostPosted: Sep Sun 05, 2021 11:50 pm 
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Location: Near Brandon, Iowa
You won't be materially improving the unit if you change to a plug-in fuse. The heater bus almost never fails and that's why probably less than 2% (my guesstimate) of radios with power transformers ever made were so fused. Count yourself fortunate that your CM rig provided protection against this unlikely failure, and leave the factory protection implementation alone.


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 Post subject: Re: Curtis Mathes Fuse?
PostPosted: Sep Mon 06, 2021 12:00 am 
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lorenz200w wrote:
You won't be materially improving the unit if you change to a plug-in fuse. The heater bus almost never fails and that's why probably less than 2% (my guesstimate) of radios with power transformers ever made were so fused. Count yourself fortunate that your CM rig provided protection against this unlikely failure, and leave the factory protection implementation alone.


Thank you Lorenz, as always your frankness is appreciated......


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 Post subject: Re: Curtis Mathes Fuse?
PostPosted: Sep Mon 06, 2021 3:04 am 
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The inrush current for the tube heaters can be significant and last for several seconds. You may have a hard time finding a suitable glass fuse that will still give protection without nuisance blowing. Keep the wire.

_________________
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Who's that swimming in the punch bowl?
It's Walter Wart, the freaky frog!


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