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Post subject: Fender Twin tripping circuit breakers...?
Posted: Sat Aug 24, 2019 11:02 am
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Hello, new to the forum so if this is in the wrong spot, my apologies.

Got a 70s silverface Twin Reverb (AA270) that is having issues. It warms up in standby, but will trip the AC breaker in the house when turned fully on. It started doing this only on the 2nd channel, with a signal applied. But now its occurring with no signal, everytime the amp is switched on, immediately trips the breaker. Loud pop, as well.

Furthermore, have tried two different circuits in the house to same result. One was a GFCI circuit in the garage and the other an AFCI circuit in a bedroom. 

Where should I start looking? Already replaced the filter caps and a few resistors that drifted from their values


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Post subject: Re: Fender Twin tripping circuit breakers...?
Posted: Sat Aug 24, 2019 2:15 pm
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Power transformer can be damaged
Because wrong ( to powerful) fuse in the amp ; more than 15 amps.

The amp's circuit may have a major failure ( power tubes ? )
The 3 amps fuse may not be the right one to protect the power transformer, because, previous owner put a 15 , 20 amps fuse.


Check the fuse and report. I'm afraid about the power transformer :(


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Post subject: Re: Fender Twin tripping circuit breakers...?
Posted: Sat Aug 24, 2019 3:35 pm
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stratele52 wrote:
Check the fuse and report. I'm afraid about the power transformer :(


+1

The only way that amp could trip a circuit breaker is if it's been over-fused, which in and of itself is concealing a *major* problem with the amp.

Put a 2.5A slo-blo type fuse in it and try to power it up. If the fuse fries, take the amp to a qualified technician and describe the symptoms to him.

Arjay

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Post subject: Re: Fender Twin tripping circuit breakers...?
Posted: Sat Aug 24, 2019 4:50 pm
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Thanks for the quick responses. Fuse is correct, 2.5A slo-blo and still intact.

Power tubes are a matched set of newer Russian 6L6's. They appear to be glowing normal in standby.


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Post subject: Re: Fender Twin tripping circuit breakers...?
Posted: Sat Aug 24, 2019 5:01 pm
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Amp fuse must trip before your house breaker because 2.5 amp is smaller than 15 amp house breaker.

Something wrong somewhere ; Look carefully if it is a 2.5 amps fuse not 25 !!!
Or amp have some mods and amp's fuse is not in the amp's circuit.

Are you sure this amp working fine before ?


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Post subject: Re: Fender Twin tripping circuit breakers...?
Posted: Sat Aug 24, 2019 10:55 pm
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GFCI and AFCI breakers will trip long before the current rises high enough to trip a regular breaker (or blow a fuse), if they detect a ground fault or arc (respectively). It's likely that if the amp was plugged into a normal branch circuit the amp's fuse would blow before the normal breaker would trip.

Most GFCI's only detect ground faults, but many AFCI's are also GFCI's.

Exactly how GFCI/AFCI breakers work is kind of a mystery to me, so I can't guess what fault in an amp would trip them.

But just saying it's entirely possible to trip GFCI/AFCI breakers without drawing excessive current.


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Post subject: Re: Fender Twin tripping circuit breakers...?
Posted: Sun Aug 25, 2019 9:13 am
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Problem resolved.

Started troubleshooting the transformer and one of the leads before the fuse had shorted against one of the tube pins. Hence why it was tripping the main AC breaker and not blowing the fuse.

It's still got the death cap wired in there and the leads from the ground switch. Would you suggest bypassing the switch and wiring the AC main directly to the fuse?

Appreciate the help, you guys. Got her back up and running and now I can enjoy this 73 tele deluxe I just got. 8)


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Post subject: Re: Fender Twin tripping circuit breakers...?
Posted: Sun Aug 25, 2019 11:16 am
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TotallyBro wrote:

It's still got the death cap wired in there and the leads from the ground switch. Would you suggest bypassing the switch and wiring the AC main directly to the fuse?




Yes, bypass the ground switch

Enjoy your great amp :)


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Post subject: Re: Fender Twin tripping circuit breakers...?
Posted: Sun Aug 25, 2019 12:18 pm
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stratele52 wrote:
Yes, bypass the ground switch


Only if a 3-conductor power cable has been correctly installed and grounded!!!

Arjay

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Post subject: Re: Fender Twin tripping circuit breakers...?
Posted: Sun Aug 25, 2019 12:27 pm
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Retroverbial wrote:
stratele52 wrote:
Yes, bypass the ground switch


Only if a 3-conductor power cable has been correctly installed and grounded!!!

Arjay


+1 it is a must a 3- conductor power cable.


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Post subject: Re: Fender Twin tripping circuit breakers...?
Posted: Mon Aug 26, 2019 7:04 pm
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strayedstrater wrote:
Exactly how GFCI/AFCI breakers work is kind of a mystery to me, so I can't guess what fault in an amp would trip them.

Short version, GFCI reads the current draw passing through the line and compares it to the current passing through the neutral. If the difference is greater than 5 milliamps (US, some countries allow 30ma), it trips, since that current is going somewhere other than the neutral.
55 milliamps can stop your heart if it hits you in the wrong place.

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