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Post subject: 1970s Fender Twin - no output, only scratching noise
Posted: Fri Mar 16, 2012 4:00 pm
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I have an old silver face that I just turned on for the first time in 10+ years. The tubes in it are at least that old.

If I switch it on, no guitar plugged in, I get a continuous scratching sound. It seems to do it more if I play with the master volume knob, but it will do it even if I leave the knob alone.

When a guitar is plugged in, I can't get any sound from the guitar through the amp. I can play with the all the volume knobs, but no luck.

I asked a local shop about it; he said "It's an old amp that doesn't work anymore. Nothing I can do."

Is that really the case, or was this guy just too busy for me?

Thanks,

Mark


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Post subject: Re: 1970s Fender Twin - no output, only scratching noise
Posted: Fri Mar 16, 2012 4:15 pm
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Can't say for sure from here but, most likely the filter caps dried up and died.

Just swapped mine out in a 67 bassman, challenging and dangerous potentially, but Mines up and running now and sounding sweet !

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Post subject: Re: 1970s Fender Twin - no output, only scratching noise
Posted: Fri Mar 16, 2012 5:29 pm
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Heh. Well, this is embarrassing.

As I said, it's the first time I'd turned this thing on in a loooong time. Have played much (except for a little acoustic) in years.

Anyway, I tried a different patch cable, and I've got output!

(he hangs his head in shame)

I still do have a problem with the master volume knob, though. Scratches like crazy whenever I touch it.


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Post subject: Re: 1970s Fender Twin - no output, only scratching noise
Posted: Fri Mar 16, 2012 7:04 pm
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Glad the amp is working, Mark ! My guess is that the amp needs a thorough cleaning. Scratchy controls are usually just signs of dirt or corrosion, not a big deal. I think Supro has the master volume remedy, let's see if he's around. BTW You probably need to hunt up another tech. Otherwise-Hammer Down and Keep Pickin' ! Art....Oh Yeah, the simple fixes are the best!

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Post subject: Re: 1970s Fender Twin - no output, only scratching noise
Posted: Sun Mar 18, 2012 6:44 pm
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Thanks for your replies, everyone.

I've tried working the master volume knob back and forth, and that seems to have lessened the scratching. I'm guessing to really get those pots clean, I have to come at them from behind the faceplate.


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Post subject: Re: 1970s Fender Twin - no output, only scratching noise
Posted: Sun Mar 18, 2012 7:24 pm
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Well yeah, Mark. But it's not a good idea to pull the chassis out, unless you have some experience with this type work. It's just a matter of your safety!!! JMO! Moving the controls back and forth is a very good idea. The wipers, in the pot, are pushing the crud off the carbon paths. Be safe! Art

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Post subject: Re: 1970s Fender Twin - no output, only scratching noise
Posted: Mon Mar 19, 2012 12:04 am
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Get yourself some De-Oxit spray cleaner -- most electronics shops and some hardware stores will carry it (or the equivalent).

Remove the knobs by loosening the set screws then spray a short burst onto each pot's shaft. Briskly rotate the shafts from stop to stop, then repeat. That should clean any spooge, crud, and/or oxidation off of the wiper and wafer within each of the pots. Re-install the knobs and you should be good to go (assuming these pots are not actually damaged or worn out).

Arjay

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Post subject: Re: 1970s Fender Twin - no output, only scratching noise
Posted: Mon Mar 19, 2012 5:28 pm
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That's a good suggestion, Arjay! Never tried that method. Suppose, if the amp is laid on it's back and a short burst, with a bunch of spindle turning. That should do the job. Guess you'd want to check the drying time on the product, before firing up the amp. Art

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Post subject: Re: 1970s Fender Twin - no output, only scratching noise
Posted: Mon Mar 19, 2012 6:31 pm
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It evaporates pretty quickly, Art -- fifteen or twenty seconds oughta do it. I never tip an amp on its back for this type of PM. Merely yank the knob, spray, and twirl. It's as simple as that.

Arjay

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Post subject: Re: 1970s Fender Twin - no output, only scratching noise
Posted: Mon Mar 19, 2012 8:22 pm
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Wow, live and learn!!! Art

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Post subject: Re: 1970s Fender Twin - no output, only scratching noise
Posted: Mon Mar 19, 2012 8:35 pm
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The active ingredient in most of these cleaners is TCE......trichlorylethylene. So use with adequate ventilation. Prolly not a good idea to smoke either while spraying the stuff.

Arjay

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Post subject: Re: 1970s Fender Twin - no output, only scratching noise
Posted: Tue Mar 20, 2012 7:53 pm
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Hi everyone, DeOxit is also available at some music stores. I got a can at Sam Trash :) If you do decide to use it be sure and have plenty of paper towels handy. Trust me on that one. :lol:

To get them clean you should pull the chassis out. The problem is you need to discharge the filter caps which can store voltage for a LONG time. If you don't know how to do this you should probably take it to a good tech for a tune-up. The guy who told you it's old sounds like a freekin' idiot, I would never go back to his place.

An amp that age needs new filter caps and bypass caps. Those electrolytics only have a shelf life of about ten years or so. The plate resistors can wear out causing crackling noise and other problems. Find a good tech and have them get that master volume out of there, and restore it to BF specs, unless it has an Ultralinear power tranny. Those cannot be put back to exact BF specs. Just my two cents.

Bigampdaddy

It's just like a car, you wouldn't run a car on thirty year old oil and filters. Amps are the same.


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Post subject: Re: 1970s Fender Twin - no output, only scratching noise
Posted: Tue Mar 20, 2012 11:46 pm
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Those two cents go a long ways!!! Art

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