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Post subject: Twin Reverb, Reverb issues
Posted: Wed Jan 04, 2012 9:23 pm
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So I recently got a late 70s twin reverb. it's the 135watt master volume version. I love it and it sounds great but the reverb is really weak. the tubes all seem to be good but i'm not 100% sure, I just replaced the reverb transformer thinking that was the problem. there seems to be a slight improvement but the reverb is still pretty shallow. I've checked all the cables multiple times, everything is hooked up correctly, the reverb tank itself is in good condition and looks brand new. I'm kind of lost as to what to do.


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Post subject: Re: Twin Reverb, Reverb issues
Posted: Thu Jan 05, 2012 3:32 am
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About the reverb tank ; .".....look brand new " Do you mean good shape or it is a replacement ?

If it is the original reverb tank, check resistors in reverb circuit and reheat solders connexions.

Replacement thank , is it the good one.

Be sure the reverb tubes are good.


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Post subject: Re: Twin Reverb, Reverb issues
Posted: Thu Jan 05, 2012 4:01 pm
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yeah the guy I bought it from said that the reverb tank had been replaced


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Post subject: Re: Twin Reverb, Reverb issues
Posted: Thu Jan 05, 2012 4:30 pm
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evan92 wrote:
yeah the guy I bought it from said that the reverb tank had been replaced

This might be your problem; the reverb tank and the reverb transformer must be matched. If not you have a poor reverb or not reverb.

Or the guy had at the same reverb problem before and take chance to replace the tank like you with the transformer ?
Look the number on the tank and see if it is the same number on the amp schematic.


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Post subject: Re: Twin Reverb, Reverb issues
Posted: Thu Jan 05, 2012 7:08 pm
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it's a 4EB2C1B which is what they use in the twin reverb


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Post subject: Re: Twin Reverb, Reverb issues
Posted: Thu Jan 05, 2012 7:29 pm
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ah wait the 4EB2C1B might be the wrong one. I can't find schematics that say which specific tank but I think it's actually the 4EB3C1B which makes sense because the 3 signifies that the tank has a longer decay than the 2


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Post subject: Re: Twin Reverb, Reverb issues
Posted: Wed Jan 11, 2012 8:05 pm
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so I ordered the proper reverb tank and now it sounds deep and lush or should I say sounded. I went over to my buddy's house and we were playing and all of the sudden the entire signal cuts out and sounds all choppy and awful. I now have no Idea what's wrong. it's not reverb related at all. it effects both channels. I turn the amp on and play but as soon as i hit it hard the signal will just cut and i can only hear anything if I play really hard and even then it is super choppy and also sounds like some sort of hyper-overdrive. I'm totally lost


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Post subject: Re: Twin Reverb, Reverb issues
Posted: Wed Jan 11, 2012 8:10 pm
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Evan -

congrats on the amp.

With older amps, there is routine maintenance that's needed, including the replacement of electrolytic filter caps, checking for caps/resistors that have fallen out of their specified range, failed power grid resistors, etc.

Best bet is to find a competent amp tech near you and have him take a look at it. Think of it as the 100K checkup for your car.

if you let us know where you're near, people can suggest amp techs they've had success with.

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Post subject: Re: Twin Reverb, Reverb issues
Posted: Wed Jan 11, 2012 9:18 pm
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I agree with Neo & Stratele, the amp needs a tech that knows these UL beasts. From your description, it sounds like the amp maybe clipping. This can be more than a simple bias issue with ultra-linear amps.

Does the bad tone go away at lower volumes? Or do you have it at all volumes, now? If all volumes... maybe bad front end (gain stage/phase inverter/input). Bad coupling cap(s) in that area can lead to DC being past or crazy voltage swings that puts the output tubes into wild distortion part of curve. Anyway, bad tone.

Good luck! And no I don't know of any good Fender UL amp techs. But, anyone that works on McIntosh amps and is good... knows about UL technology.


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Post subject: Re: Twin Reverb, Reverb issues
Posted: Wed Jan 11, 2012 10:50 pm
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It's more dependent on volume. If I turn off the amp and turn it on it will sound fine until I either turn up more or strum my guitar really hard, once I do that then I get the choppy, awful tone. It seems like it has to do with how much signal is going through the preamp. another weird thing is that if I either turn it off or just kick the cabinet a little then it goes back to normal until I hit the amp with a strong signal.


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Post subject: Re: Twin Reverb, Reverb issues
Posted: Thu Jan 12, 2012 12:36 am
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Ahh, yes the kick trick is cool, Evan. Actually, I'm going to go with dirt(oxidation) or a weak solder joint. Art

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Post subject: Re: Twin Reverb, Reverb issues
Posted: Thu Jan 12, 2012 8:31 am
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+1 on solder joint

Definitely sounds like a bad connection somewhere.

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Post subject: Re: Twin Reverb, Reverb issues
Posted: Thu Jan 12, 2012 3:03 pm
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I was going to open it up today so how should I go about finding the bad solder?


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Post subject: Re: Twin Reverb, Reverb issues
Posted: Thu Jan 12, 2012 5:45 pm
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well great I found a spot where the lead of the resistor had broken off, so I soldered it back together. I turned it back on and now it doesn't work at all. it just emits a soft hum.


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Post subject: Re: Twin Reverb, Reverb issues
Posted: Thu Jan 12, 2012 6:10 pm
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Sounds like you might have soldered something that shouldn't be soldered, or soldered to the wrong place.

Are you sure that something had actually broken off, and that you know where it should be soldered? Do you really know what you are looking at, and have the schematics, or are you just guessing?

Maybe post a picture of what you did, be careful guessing if you aren't sure of what you are doing.

This should be your schematic, maybe you can identify the part that you soldered.
http://www.prowessamplifiers.com/schematics/fender/Twin_Reverb_sf_135.html

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