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I need some help quieting down a noisy amp.
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Larry Mal
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#1
18th April 2013
Old 18th April 2013
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I need some help quieting down a noisy amp.

Hey all, I'm not all that knowledgable about amps, and I have a 1980 Fender Twin, this is the master volume model in the silver face.

It's kind of loud, there is a buzzing sound with it, and I can tell you it's not a ground issue, nor is it with the guitar. It's there in the background relatively all the time, it does increase somewhat when the volume is increased. The noise gets more intense when the "Bright" switch is turned on.

All the inputs, the reverb, the pedal and the vibrato work as they should... in short, I'm pretty sure it just needs what amounts to a tune up. I'm not real skilled at that, and I'd like to take a crack at it before I take it to the shop because I'm not rolling in money and I really just want to quiet this down in order to sell it. I will take it in, of course... but I'd like to take a crack at it first.

The main tubes are Sovtek, no idea how old they are. I can obviously put new tubes in, I don't know anything about biasing the amp and probably don't know how to isolate any defective capacitors, and I'm not sure if it's a good idea to even try.

Any advice? How should I even start going about this?
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19th April 2013
Old 19th April 2013
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Quote:
Originally Posted by Larry Mal View Post
I don't know anything about biasing the amp and probably don't know how to isolate any defective capacitors, and I'm not sure if it's a good idea to even try.

Any advice? How should I even start going about this?
With your statement above, I think you've answered your own question. Guitar amps contain lethal voltages; poking around could get you electrocuted or worse. Besides changing preamp tubes to see if it's a faulty tube, I'd leave the rest to the experts.

I would suggest taking it to a competent Fender amp tech. Could be a bad tube, or it could be 33 year old electrolytic filter caps that need to be replaced (my bet).

FYI I will only change preamp tubes on my amps. Anything else, and it goes to the shop.
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Larry Mal
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19th April 2013
Old 19th April 2013
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Fair enough... I do know that amps can be dangerous, I wasn't sure if biasing was something one could do safely or not. I'm not going to be poking around, that's for sure... I'm honestly not even sure what amount of work one would do before an expert needed to be called in, is why I ask.

So, I can put a new set of tubes in, hope for the best there. There are sets of tubes that are said to be pre-biased together, do you know much about that? Is that just a claim or is that likely to be true?
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19th April 2013
Old 19th April 2013
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Quote:
Originally Posted by Larry Mal View Post
Fair enough... I do know that amps can be dangerous, I wasn't sure if biasing was something one could do safely or not. I'm not going to be poking around, that's for sure... I'm honestly not even sure what amount of work one would do before an expert needed to be called in, is why I ask.

So, I can put a new set of tubes in, hope for the best there. There are sets of tubes that are said to be pre-biased together, do you know much about that? Is that just a claim or is that likely to be true?
Yeah, you're talking about matched sets. Those are just for power tubes. You don't bias preamp tubes, as they bias themselves. You'll want to make sure if you replace the power tubes to use matched sets. It basically just means that the two or four or however many power tubes you install are pretty close to each other. That helps reduce hum and other issues. But if you replace the power tubes, you'll want to bias them so they last a long time and sound good. And for that, you'll need a tech. So I wouldn't even buy power tubes. Just replace some or all of the preamp tubes and if that doesn't fix it, then take it to a tech. Let them mess with the power tubes, filter caps, and whatever else may be wrong. An amp of that age is probably due for some maintenance. So I'd save up a few hundred bucks and get that taken care of. These amps can last for a hundred years or so if taken care of properly. But like anything, they do require regular maintenance. And yours sounds about ready for a major tune up.
Larry Mal
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19th April 2013
Old 19th April 2013
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Sounds like it. It's a good amp, well worth fixing up a bit. I was intending to sell it, but potential sales have balked, and it's either sink a little more money into it and make a little more or dump it. I'll probably just store it and keep it.
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