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Post subject: Improper implemenation of fuses
Posted: Tue Apr 29, 2014 3:37 pm
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Off another amp board. This amplifier shorted out and set off the smoke detectors is this owner's house. That's what saved his house and life. The amp was on fire, as the alarms sounded.

Notice the two onboard fuses? Neither worked. Both are still intact. An example of an improper implementation of fuses in a circuit. I've seen similar, though not as drastic, situations in modern amps with fuses on the circuit board. Where parts are fried, but the fuse(s) did not pop.

The purpose of these fuses are to save the PT (the round, burnt large toroid). Notice the blown large filter caps, too. Massive short circuit current draw. It only took a matter of minutes.

NB: Be sure to check fuses in any used amp you buy. A 20-amp car fuse can result in similar meltdown.


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Post subject: Re: Improper implemenation of fuses
Posted: Thu May 01, 2014 12:04 pm
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that's a good point. The only vintage amp I've ever owned came with foil wadded up in the fuse holder on the back panel. It says right below what the correct fuse type is, and fuses are pretty cheap. I don't understand what people are thinking sometimes. :?

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Post subject: Re: Improper implemenation of fuses
Posted: Thu May 01, 2014 3:28 pm
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Let me axe you sumthin.

Any opinion about whether I should discard the accessory plug on the back of my Twin while I'm in there installing a grounded cord?
Would be nice to have it functioning for something small......but maybe someone's seen something counter to this.


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Post subject: Re: Improper implemenation of fuses
Posted: Thu May 01, 2014 4:25 pm
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yomammaaho wrote:
Let me axe you sumthin.

Any opinion about whether I should discard the accessory plug on the back of my Twin while I'm in there installing a grounded cord?
Would be nice to have it functioning for something small......but maybe someone's seen something counter to this.


I always leave the AC convenience outlet fully functional when refurbishing a vintage Fender amp though I never recommend using it for any high-demand devices such as a second amp, toaster oven, cuisinart, etc. They're actually ideal for powering a pedal board or a stand-alone tuner. The later silverfaces (1972 forward) are equipped with a grounded 3-conductor receptacle.

Arjay

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Post subject: Re: Improper implemenation of fuses
Posted: Wed May 07, 2014 12:32 pm
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yomammaaho wrote:
Let me axe you sumthin.

Any opinion about whether I should discard the accessory plug on the back of my Twin while I'm in there installing a grounded cord?
Would be nice to have it functioning for something small......but maybe someone's seen something counter to this.

I wish more amps had a 'courtesy plug'. They're just damned convenient. There are three prong versions available as replacement.

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Post subject: Re: Improper implemenation of fuses
Posted: Wed May 07, 2014 2:16 pm
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mhowell wrote:
I wish more amps had a 'courtesy plug'. They're just damned convenient. There are three prong versions available as replacement.


+1

Back in the days of the blackface/silverface era, all Fender amps with the exception of the Champ, Vibro Champ, and Bronco featured an AC convenience outlet. These receptacles were rated for 200 watts and from circa 1972 onward were the grounded 3-conductor type.

Arjay

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