Help With Original Vibroverb 15

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by frankiestarr, Apr 1, 2008.

  1. frankiestarr

    frankiestarr Supporting Member

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    Hi everyone

    I have a original 1964 fender vobroverb that I have played for 6 years or so as my main amp. It was heaven in a box....One day, it started making dome weird sputtering sounds at my gigs, and started to bother me a little. I took to a local tech, and he started trouble shooting it. He had a hard time pin pointing the problem. he ended up replacing numerous parts, and finnally the noise went away, and so did the tone...It sounded real thin, and lost that cool sag it had. So, I tried anaother tech, and he put all NOS original parts and basically rebbuilt the entire amp, it sounded just a little better but not like it did originally.
    So now I have a real vibro-verb in near mint condition that just sounds thin and harsh. The break-up is hard, needs more sag and warmth. I tried various tubes, didn't help... Can anyone give me some direction on how to get this thing sounding like it used to????:worried
    Thanks
    Frankie Starr
     
  2. GuitarsFromMars

    GuitarsFromMars Member

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    Take it to an amp guy who knows old Fenders...they're far and few between.But if he's worth his salt,he will repair your amp.
     
  3. PRNDL

    PRNDL Member

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    I agree with that guy from Mars.

    Coincidentally, last week Larry Rodgers showed my his latest purchase - a Vibroverb in fantastic condition (a '65 if memory is good). This amp had KT66's and had a lush reverb and fantastic smooth crunch. It had one of the best tones I've heard.

    As with many of these old Fender amps, the circuits are simple and everything contributes to the tone (resistors, capacitors, electrolytics and tubes). It takes a finely tuned ear to know what those amps need.

    In your case, it sounds like the output section is too stiff, which means changing the output tubes and rectifier. A good tech knows what tubes are appropriate for that amp. The thin sound, however, is much harder to sort out.

    Many people mail their amp(s) to Larry ... he's one of the old guard and has been a tube guitar amp tech for over 20 years.
     
  4. VikingAmps

    VikingAmps Member

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    Do you remember what parts he replaced? If it started sounding thin after a particular part was replaced theres your clue.
     
  5. TonalVision7

    TonalVision7 Member

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    I would find someone who has a great sounding Vibroverb and measure the values of the components in the amp such as Caps, Resistors, B+ Voltages etc, Then buy and measure a bunch of the same components to find the exact values of the components, and use the matched components. This can get expensive if your paying a tech because it is very time consuming. You can't really put a price on great tone though. What type of tube rectifier is in the amp? If it is a 5U4 rectifier you could try a NOS 5V4 rectifier tube in for more SAG.
     
  6. jetlag

    jetlag Member

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    I think the idea of a substitute rectifier tube and rebias to induce some sag is a great idea. I did that with my old tweed bassman. I finally broke down and replaced the electrolytics in the amp. To my dismay, the tone went, it almost sounded like a reissue. So I put a GZ37 (a 5R4G would be a good sub too) and rebiased and got much of the warmth and sag back. Enough to enjoy playing the amp again. After about 6 months, out of curiosity, I tried the GZ34 and rebias and, voila, the sound was about like it originally was. So maybe that's part of your problem. Try a 5R4G rectifier and bias the amp kinda warm - at least 60% to 65% and see where that takes you.
     
  7. Swarty

    Swarty Member

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    Have you plugged in a different speaker?
     
  8. phsyconoodler

    phsyconoodler Member

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    Firstly,what is the bias set at?A new set of filter caps won't make the amp sound bad,unless they are the wrong values.A too cold bias setting will do exactly what you are describing.Thin and lifeless tone,where it was fat and toneful before.
    Some basics need to be addressed here before drawing conclusions.
    What tubes are in the amp?If the tubes are cheapo specials that may have something to do with it too.
    You need to know what the bias is,what tubes it has now,and what the plate voltages are.Then you need to see what capacitors were changed and what values they are.Then we can help you find the lost tone.
    Some techs can't even play guitar,but they do great work on paper.They don't know how to test an amp for tone,but know how to change a capacitor and how to use a scope.I know a bass guitar player/tech who fixes guitar amps and tests them with his bass!Needless to say,they all sound like bass amps when he's done!
     

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