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Post subject: Opinions requested: My amp is developing distortion
Posted: Fri Nov 30, 2012 12:09 pm
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My "73 Vibrolux Reverb (yes, original owner) has been developing a harshness/distortion, generally in the mid to upper range. Bass seems clean. Not severe, but noticeable. I still want that warm clean sound. I play at volume 4 or 5 in the house. So I have installed new tubes (didn't change much) and have examined the two 10" original speakers (nothing obvious observed). The speakers do ohm out correctly.
So now what? Not sure where to go next. Speakers or electronics??????? Or something else?
Thanks in advance....................


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Post subject: Re: Opinions requested: My amp is developing distortion
Posted: Fri Nov 30, 2012 4:02 pm
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While I am certainly no expert amp tech, did you set the bias on the new power tubes? Has it ever had a cap job?...if not might start with that as it is overdue for one.

One word of caution, if you don't know how to set the bias, take it to a qualified tech familiar with Fender amps of this era.

FWIW

T2

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Post subject: Re: Opinions requested: My amp is developing distortion
Posted: Fri Nov 30, 2012 4:19 pm
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Thanks Stratman. The capacitor is a good thought. As to bias, Fender support told me recently this particular amp (2 power tubes) does not need bias adj. I did replace with matched set of tubes however. I will investigate the cap angle. Hope I don't get shocked.............


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Post subject: Re: Opinions requested: My amp is developing distortion
Posted: Fri Nov 30, 2012 4:30 pm
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Although that amp does not have an adjustible bias level, it does have a bias balance pot that should be adjusted when teh tubes are replaced. Guess Fender Support needs to learn a little more about the older amps. :lol:

http://www.ampwares.com/schematics/vibr ... _aa270.pdf

Original owner + a 39 year old amp = mandatory cap job or at least a thorough check of all the caps.

Suggest you take it to someone familiar with old Fender amps.

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Post subject: Re: Opinions requested: My amp is developing distortion
Posted: Fri Nov 30, 2012 5:11 pm
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New tubes !!!! check also for the Phase inverter tube . the 12AX7 close to the output tubes


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Post subject: Re: Opinions requested: My amp is developing distortion
Posted: Fri Nov 30, 2012 6:54 pm
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Pondo, I agree with what has already been advised. The problem does not seem to be very serious, at this point. So this is the time to get it into a good tech for a thorough cleaning and check-up. The filter caps and bias cap R&R is the route I'd go, at this time. Just to avoid having to revisit the tech and having to pay another bench charge. Be sure to request quality-tested caps for your amp. Art

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Post subject: Re: Opinions requested: My amp is developing distortion
Posted: Fri Nov 30, 2012 7:03 pm
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One other thing. If those are the original speakers, sometimes they can distort the details when th paper cone gets brittle. May want to try an external cab. Just to rule this out.


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Post subject: Re: Opinions requested: My amp is developing distortion
Posted: Sat Dec 01, 2012 11:58 pm
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For sure!!! Beemer is right, spot-on!! You know, Pondo, we haven't walked a guy through a maintenance and rehab program, for a while. If you're willing to invest in some learning(read safety), patience, and the necessary chems and components; the folks here, are probably willing to help.(Are you guys up to it?) Otherwise, a good tech is the ticket. Art

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Post subject: Re: Opinions requested: My amp is developing distortion
Posted: Sun Dec 02, 2012 12:17 am
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Art, it's a love affair with the tone of vintage amps. I think we all love it when a poster gets his amp in the Fender groove. :D


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Post subject: Re: Opinions requested: My amp is developing distortion
Posted: Sun Dec 02, 2012 10:53 am
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I want to thank again all those who responded to my post. Yes, I do love that vintage sound and cannot forfeit it. I took the consensus advice and delivered to a amp tech. It was interesting in that he does not seek business, and was hesitant until learning that the amp was a Fender. But that wasn't enough alone. He asked how old? When I told him a '73, well I could tell he was now quite agreeable. And later disclosed that the new ones (any brand) aren't really made to be worked on. I feel fortunate in that I found him. I see many posts of people searching for a tech in their area. My metro area is almost a million, so what does that tell you?
I'll see how it goes. For the record, he says a cap job would be about $120. That the value of this amp ('73 Vibrolux Reverb, silverface, was $1100. Maybe more because he recently sold similar in lesser condition for that. Of further interest, the smaller ones (champ, princeton etc.) are bringing more than the bigger amps, such as mine or twin reverbs etc. Ok folks, Fender on.......


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Post subject: Re: Opinions requested: My amp is developing distortion
Posted: Sun Dec 02, 2012 2:46 pm
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Pondo657...Sounds like you may have found a great tech. Anybody hesitant to work on the newer stuff and had to be convinced because it was an old Fender Amp should tell you everything you need to know about him. Consider yourself lucky, good techs are not easy to find.

As for your vibrolux reverb we would love some pics of it when you get it back. We love Fender Amp porn :lol:

T2

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Post subject: Re: Opinions requested: My amp is developing distortion
Posted: Sun Dec 02, 2012 3:06 pm
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pondo657, Good luck! Any Q's, post 'em.

:mrgreen:


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Post subject: Re: Opinions requested: My amp is developing distortion
Posted: Sun Dec 02, 2012 5:55 pm
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Glad you found a good tech, Pondo.

Art


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Post subject: Re: Opinions requested: My amp is developing distortion
Posted: Mon Dec 10, 2012 10:25 am
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The amp is back from the doctor. On time as he promised. His report is:
Two loose ground wires. Two bad power supply caps. And one failing tube. The tube is a mystery. It is a 12AZ7A, RCA (Original). It does test bad, but he says it is not the tube specified for where it was located. Probably it was me messing up, yet I was so careful in swapping tubes. At any rate the amp sounds great now. Of note, the volume is seemingly higher now, at a given knob setting.


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Post subject: Re: Opinions requested: My amp is developing distortion
Posted: Mon Dec 10, 2012 10:56 am
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Outstanding. :D

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