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Post subject: Fender Supersonic Twin - No Power - Blown fuse?
Posted: Sat Jan 12, 2013 5:20 pm
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I'm hoping one of you expert might be able to help. I have a 6 month old fender twin supersonic amp. I did some recording tonight. After finishing, I was showing the engineer the amp has he had not see a supersonic. I was trying to show him the bias lights on the back. So I switched it on standby and then off. I then switched it back on, and there a little flash on the bias lights but then everything went blank. Tried a switching it off and on again but nothing. I have tried 2 separate leads to no avail. Is this just a simple fuse blowout? If so, aslong ad it's the right amp, can I just stick any brand fuse in there? The tubes are almost brand new, so it shouldn't be them right? Also, can't it run on 3 tubes or something? Let me know if you can help


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Post subject: Re: Fender Supersonic Twin - No Power - Blown fuse?
Posted: Sat Jan 12, 2013 5:44 pm
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Is the pilot light on the front of the amp lit? If it is not, it could be a fuse. An 8 amp slo-blo fuse should be used.

If the pilot light is lit, I suggest you send or take it back to the dealer under warranty.

The amp might run on three tubes but it is not recommended and will probably sound like crap.

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Post subject: Re: Fender Supersonic Twin - No Power - Blown fuse?
Posted: Sat Jan 12, 2013 9:45 pm
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I believe that the fuse should be a normal, fast-acting type as the "F" indicates (F8A). This will be marked on the fuse itself, and an "F" indicates a fast-acting, while a "T" indicates a time-delay (slo-blo). :idea:

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Post subject: Re: Fender Supersonic Twin - No Power - Blown fuse?
Posted: Sat Jan 12, 2013 11:51 pm
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You're right. Didn't read close enough. So used to using slo-blo fuses.

The whole issue is moot if the pilot light is still lit, though. Even if it is out, I would be questioning why the fuse blew. :wink:

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Post subject: Re: Fender Supersonic Twin - No Power - Blown fuse?
Posted: Sun Jan 13, 2013 2:33 am
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Sorry I should have mentioned that the pilot light is not on. Is it easy to switch these fuse? Because I was recording the amp was on for about 4 hours, maybe turning it off and then on relatively quickly caused it to short??Also, this fuse you specified, can you get that from general hardware stores?


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Post subject: Re: Fender Supersonic Twin - No Power - Blown fuse?
Posted: Sun Jan 13, 2013 2:52 am
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Not in hardware store , see Radio Shack or other electronics parts store. Always use the right fuse.


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Post subject: Re: Fender Supersonic Twin - No Power - Blown fuse?
Posted: Sun Jan 13, 2013 3:08 am
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Is it hard to replace?


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Post subject: Re: Fender Supersonic Twin - No Power - Blown fuse?
Posted: Sun Jan 13, 2013 3:27 am
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Rusty545 wrote:
Is it easy to switch these fuse?

The fuse socket is right next to the power cord. Make sure the amp is unplugged !! Then just unscrew the fuse cap, you'll need to press in on the cap while turning it, & swap the fuses. I'd do that first before worrying about anything else.


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Post subject: Re: Fender Supersonic Twin - No Power - Blown fuse?
Posted: Sun Jan 13, 2013 8:16 am
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Rusty545 wrote:
...maybe turning it off and then on relatively quickly caused it to short??...


You mean "caused it to open", as a fuse opens when the current through it exceeds the rating.

Very likely, because there is a thermistor in series with the fuse. The thermistor is a resistor that changes value with heat, and when the amp is cold at start up, the thermistor resistance is high to limit the inrush of current that normally occurs when a transformer has voltage applied. Once voltage is applied to the amp, after a short time, the resistance of the thermistor decreases to allow normal current flow in the circuit. If the amp is turned off and then immediately turned back on, the thermistor doesn't have enough time to cool and return to it's higher resistance so there is no limiting of the inrush of current to the transformer in that case.

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Post subject: Re: Fender Supersonic Twin - No Power - Blown fuse?
Posted: Sun Jan 13, 2013 8:26 am
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I've switched my amps (one with tube recitifier and no thermistor, the other with solid state rectifier and a thermistor) on and off quickly with no problems. To do this and blow an 8 amp fuse certainly makes me wonder what really happened.

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Post subject: Re: Fender Supersonic Twin - No Power - Blown fuse?
Posted: Sun Jan 13, 2013 11:30 am
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Aye but the amp was on for about 4 hours, so it was red hot. I've turned it on and off previously and it has been fine? Either way I really appreciate all the help everyone on this page has given me. I'd be clueless. I'll let everyone know if the fuse works


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Post subject: Re: Fender Supersonic Twin - No Power - Blown fuse?
Posted: Mon Jan 14, 2013 4:57 am
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Rusty, If that amp blows another new fuse (try to use Littelfuse or Buss glass types) --- it may need recapping of the filter caps. Esp the ones in the first stage (C55 and C56).

That's been my experience with amps that seem to work fine, hold a proper idle bias, and are not tube eaters.

http://support.fender.com/schematics/gu ... _Rev-B.pdf


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