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Post subject: My 1967 Fender Super Reverb is blowing fuses
Posted: Wed Sep 08, 2010 7:03 pm
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Greetings,

This is my first post and I know that someone out there will be able to help me.

I have a blackface '67 Fender Super Reverb in my collection that is in very-very good condition. The amp was purchased new and belonged to my father who gave it to me about eight years ago (along with his very clean candy apple red '65 Jazzmaster).

Anyways, I recently had some maintenance done; new caps, electrolytics, tubed and biased. Up until this point I have never had a problem this amp nor had my father. The tech talked me into replacing the caps and electrolytics since they were the original ones and a few were "leaking" The tubes had been replaced and biased prior and everything worked fine. Now it blows fuses all the time.

I am able to turn the amp on, I let the fuse "burn" and the tubes heat for a minute or so before I take it off of standby. Once I flip it off of standby, I am able to see the amp be alive for anywhere between 20 seconds to 1.5 minutes, the fuse blows regardless if I have a guitar plugged in or not.

I have replaced the rectifier tube as well. This amp is not used heavily at rehearsals or gigs, but does make appearances on occasion.

The amp tech I am using is a certified Fender tech, I have taken it to him several times and he seems stumped. The fuse will not blow at his place, but as soon as I try it anywhere else it will blow right away. Could this be because he has it plugged into a wall of crazy volt meters and stuff? The tech recently ordered a new "Output Transformer" for my amp.

Does anyone else out there have a second opinion? Why would the output transformer suddenly go bad? I wish I knew more about amp circuitry, any help or advice that you could give me is greatly appreciated. This amp is one of my favorite pieces of equipment, I just want it work again.

Thanks for your help,

Ross


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Posted: Wed Sep 08, 2010 7:57 pm
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Location: In a house....unless I'm at work....then I'm in a shop.
Why is he replacing good part?

I don't understand that at all.

Is there another Fender amp tech in town?

If not, call the music stores in your town and ask who they recommend.
It's time for a second opinion.

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Posted: Wed Sep 08, 2010 8:09 pm
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Thanks for the reply.

Sorry for my lack of detail. The tubes needed to be replaced, when I took it to him for the amp to be tubed and biased he convinced me to put in the new caps and electrolytics.

There are no other Fender amp techs in the area, this is the go to tech for the music store. I trust the guys at this store. But they also have no ideas as to what is wrong with the amp. We (the music store and I) have considered shipping the amp to another tech out of state but the cost is high and I am very shaky about shipping my prized Super to unknown territory and risking damage.


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Posted: Wed Sep 08, 2010 8:12 pm
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Welcome to the forum Sas ! First thing I'd try is removing all the tubes,with the exception of the rect. Switch amp on and standby to the play mode. This will let you know if the power trans and filter caps are good. Art

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Posted: Wed Sep 08, 2010 8:40 pm
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I suspect something in the biasing circuit (incorrectly polarized cap?).

Do as Art suggests to start running the problem to ground.

HTH

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Posted: Wed Sep 08, 2010 8:58 pm
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If you can turn the amp on for several minutes, before the fuse blows... it maybe instability. Does it lose volume or seem to get excessively hot before the fuse blows? You may want your tech to check the grid stopper and screen resistors values. These are resistors are placed on the power tubes to help stabilize the amp. If they drift far outta specs they may stop doing their job.

Parasitic oscillations sometimes happens after the amp's been on for awhile. Often you can't even hear the amp becoming unstable (no odd harmonics, etc) . Anyhow, connection dressing around the sockets, placement of components, soldering, & grounding schemes usually can eliminate most instabilities.


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Posted: Wed Sep 08, 2010 9:45 pm
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What sends up a red flag, for me, is that the amp works fine at the shop. So we're probably looking at a filtered & regulated power supply(120vac@60hz), which is not always the case in the real world. My wall voltage is 127vac(in NE IL). I should have asked you,Sas, if the power cord has been changed to a 3-prong and whether or not the .047uf/600vdc cap on the ground switch has been checked or removed ? I agree with Arjay and BMW, in fact, the bias diode and filter cap were my first suspects. As far as the output trans goes, heat is the biggest problem, corrosion would come in second. If say the amp was operated with an extension speaker, this would be a real issue. Art

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Posted: Thu Sep 09, 2010 2:44 am
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Sasquatch,
Your tech is a very very bad one. Find another one. He is your problem. Ask to some guitars players for another teck, take your time but never return to see this guy. He work like a beginner.
I think is only the store is "approved Fender" not the guy.
And follow what aclempoppi said about the tubes.

My opinion is the output tubes is wrong biased and/or short that why the fuse blow after a minute of "playing".

Take your time you have a vintage amp don't scrap it


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Posted: Thu Sep 09, 2010 5:25 am
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Yeah,listen to the guys here before you take it back to your "tech"...something isn't right and I suspect it's the result of his work.
If he's going to start replacing things like an OT just because he can't figure out the problem,you will wind up spending lots of money that you shouldn't have to...and the amp could be butchered internally.
It can be traced down,and the good guys here can help.


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Posted: Thu Sep 09, 2010 7:11 am
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Rebelsoul wrote:
Yeah,listen to the guys here before you take it back to your "tech"...something isn't right and I suspect it's the result of his work.


That knuckle-dragger should seek an alternate career in the food-service industry.

Arjay

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Posted: Thu Sep 09, 2010 1:58 pm
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Hey thanks for all your help!

I will not be returning to the "bad" tech.

I am going to take your suggestions to the only other tech in town that is not a certified fender tech but he does do good work and knows his stuff. I have had him work on a keyboard and pedals before, a few of my friends have taken their amps to him and everything works great. I have a lot more faith in this guy, especially after you guys have given me a little direction.

I'll let you know how things pan out.

Cheers!
Ross


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Posted: Thu Sep 09, 2010 3:00 pm
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Best of luck, Ross.

Report back and let us know what the new tech discovered.

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Posted: Thu Sep 09, 2010 6:16 pm
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Hey Ross, did you try pulling those tubes and testing the amp, or did you run out of fuses ? I wouldn't be too tough on the first tech. It's easy to overlook things in these amps or put in faulty new parts. The fact that the tech couldn't replicate the problem in the shop is interesting, especially when the failure occurred before and after you took it in. BTW How was the amp before the first viit to the tech ? Art

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Posted: Thu Sep 09, 2010 8:14 pm
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I ran out of fuses, I am going to pick some more up tomorrow afternoon. I will not be able to test it for a few days because I will be out of town over the weekend with the band.

The amp was fine before the first vist, with the exception that the tubes needed to be replaced and biased. I replaced both the output tubes and the preamp tubes. I have a feeling that one of the new caps or electrolytics is bad.

I know the first tech does good work and I know he knows what he is doing. I just think a second set of eyes checking things over might catch something that was overlooked. I have no hard feelings towards him, he has worked on my '64 R600C Lectrolab amp along with other equipment. I just think he could be overlooking something.

Thanks for you help! I'll let you know how the amp does without the tubes after I try it.

Ross


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Posted: Fri Sep 10, 2010 5:37 am
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You're right about a second set of eyes catching something wrong.Sometimes when you're looking for a new problem,something that you could have done wrong is overlooked...it's the "can't see the forest for the trees" thing.
Even after you have rechecked your own work,you might not see the obvious.


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