Vibro Champ Mods

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by Rivi, Aug 11, 2008.

  1. Rivi

    Rivi Member

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    Today i replaced the old two wire cord with a three wire grounded cord.Now the amp is whisper quiet,i had a bit of surf noise in the back ground.
    I also added a 50 ohm 5 watt carbon resistor in the 5v6 circuit.I wanted to see if it would change the sound any.It seems to have made the amp not break up as quickly.

    Is there any mod that i can do to get this amp up to 8 with breaking up?It starts breaking up a 6 now.Thank You
     
  2. wahfreak

    wahfreak Silver Supporting Member

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    Not exactly a mod, but put a 5751 in V1. It has less gain so it wil break up less. Also put in a new Weber speaker.
     
  3. Faustine Amps

    Faustine Amps Member

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    Where did you put the 50 ohm resistor?

    I'm not sure you're going to get much headroom out of a vibro-champ. Part of it's charm is the way it breaks up when you crank it. Nature of the beast. A 5751 (or 12AY7) will surely help.

    Regards,
    Tim Gregoire
     
  4. Rivi

    Rivi Member

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    I added it in front of the 470 ohm(actually measures 500)so total is 550 ohms in that circuit.That changed it some,it doesn't quite break up as quick.What causes the early break up in this amp?I've had other old amp using 6v6 tubes that didn't do this,but they used two 6v6 tubes.I've never owned a champ before.

    By the way i'm really suprised at the quality of this amp,after 40 years all the original caps resistors etc all seem good.Its quiet as a new amp with absolutely NO HUM or noise!I beileve it still has the original rectifier tube also.
     
  5. Groovey Records

    Groovey Records Member

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    Tick Tock Tick Tock

    My Favorite mod is sometimes I turn the volume control from 9.5 to 9.3

    MUST CHANGE SPEAKER
     
  6. Rivi

    Rivi Member

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    I'm going with a 10 inch jensen mod 10-35 8 ohm.I tried it with the jensen already from my other cab but it still breaks up early.I may just start changing things in the circuits till i get some idea what is possible with these tube circuits.
     
  7. RedRock

    RedRock Member

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    Here's a mod I did about a year ago by request on a Vibro Champ:

    Punched out the chassis for 4 9-pin tubes and 2 octal sockets;
    Gutted the chassis and installed a Princeton Reverb eyelet board;
    Installed a David Allen beefier power transformer and output transformer;
    Installed a solid state rectifier and a reverb transformer;
    Used 2 6l6 power tubes;
    On the back chassis panel, installed the fuseholder, stand-by switch,
    2 speaker jacks, a master volume, reverb control, mid control
    and the 4 RCA jacks for reverb send and return and footswitch
    control of reverb and vibrato;
    Cut the speaker board for a 10" speaker (50 watt)
    Installed a short reverb tank;
    Removed the multi-element cap and replaced it with caps in the
    chassis;

    Result: A Princeton Reverb with 6l6 tubes, a master volume
    and a mid control in a Vibro Champ cabinet. The front faceplate
    had a perfectly stock appearance.
    The owner had a 12" EV speaker in an extension cabinet for larger rooms.
    He wanted a "wolf in sheep's clothing" amp that was as portable as
    possible.
     
  8. Rivi

    Rivi Member

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    Sounds very cool.
     
  9. Rivi

    Rivi Member

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    My Tung Sol 6v6 came after i posted,I pulled the new Electro Harmininx out and put this 50 year old tube in.Wow much nicer,it doesn't break up near as quick and the sound is much cleaner.
     
  10. Axekisser

    Axekisser Member

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    If I'm reading right, you put the 50 ohm in series with the cathode resistor for a total of 520 ohms. Good practice is to make that resistor a 1k ohm. I usually use a ceramic 3-5watt. It lowers the bias a bit as these run hot with today's voltages. Using the 1k will get the tube to dissipate around 12 watts or so instead of the 14+ with the 470 ohm.
     
  11. Rivi

    Rivi Member

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    Its not 470,its 500 actual ohms plus the 50 i added.The big change was replacing the tube.It cleaned it up quite a bit.The Electro Harmonix tube distorts too much for what i like.The old stock Tung sol is much better.I might order a RCA 6v6 to try .
     
  12. Groovey Records

    Groovey Records Member

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    yes RCA Power Tube a Black Plate Anos would be a bargin.

    Really though ask anyone. The biggest bang for the buck after a cap job is the Speaker swap.

    good Luck

    Those Babys give up the goods
     
  13. Rick1114

    Rick1114 Member

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    I like the RCA 5Y3/6V6 combo in my 66 VC - chimey. I would also get a cap job and swap the speaker (I find those Jensons to sound thin in that amp, but it sounds great in the 1957 GA-5 I just picked up). The only other thing I did was have 1/4 speaker jack installed incase I ever need to use a cab and put all the original parts in a plastic bag. I wouldn't really mess with other mods, but tech gave me this tip, and think this is for increasing headroom:

    One last tip: Try a 5881 in place of the 6V6, and
    increase the cathode resistor to a 5 watt 470. This is an old trick on
    champs from "back in the day".


     
  14. Rivi

    Rivi Member

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    I'm gong to try disconnecting the negative feed back circuit.Weber does it on their amps for more volume and punch.They use a push pull volume knob to do it.
    Funny you mentioned a 5 watt 470 ohm resistor because while i was in there changing the cord i noticed that resistor looks under sized wattage wise.Good idea there.Thanks
     
  15. Faustine Amps

    Faustine Amps Member

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    So... judging by your posts in this thread, it appears that you're satisfied with operating the amp on 40 year old caps, you're going to replace the 470 ohm, 2 watt resistor with a 470 ohm, 5 watt resistor, you are going to replace the 3.2 ohm Oxford speaker with a 8 ohm Jensen speaker, and you're going to remove the negative feedback circuit.

    I'm not sure why you've asked for expert advice on maintaining and modifying this amp (in previous threads) if you have no intention of listening to that advice, but apparently if it sounds good that's all that matters. Oh well... it's your amp, have fun.

    Regards,
    Tim Gregoire
     
  16. Rivi

    Rivi Member

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    I ordered new caps 25uf 50v 4 of them but i'm not sure why i should change them if they are working ok?Another thing is everyone seems to have a different opinion on with cap values to use.Some say use 25v for bette sound others 50v then others 100v.

    I like everyones input and will use the info to try and get a sound i like.I know my old band master had a push pul volume and i'm sure all it did was cut the negative feedback circuit in or out.
     
  17. Rick1114

    Rick1114 Member

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    I think most say 50V just to be on the safe side as the original 25V was a little underspec'd, but never really fail either. Tonally I was told there may not be much difference. I found when I went on a modding frenzy with my DRRI, that the stock circut was sounded best. But that was a reissue amp - I wouldn't want to learn that on a vintage amp, even if it was a early Silverface. These small amps have their own sound and I would play it stock for long while before making changes - it will grow on you I think.
     
  18. Groovey Records

    Groovey Records Member

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    Rivi,

    I think you have just gotton some very good advice.

    If this amp is to be a keeper Reprioritize you ideas and protect your investment Saftey first, sound theory for stabilizing your platform Second and please dont make a molehill out of a mountain.

    The Champ does what it does and can be tweeked to do that in different ways- Don't try to change the amps true character.

    I do appreciate the wolf in Sheep[s clothing post but it is no longer a champ
     
  19. Rivi

    Rivi Member

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    Honestly with the 50 ohm resistor adeed in the 6v6 circuit and the Tung Sol 6v6 i'm very happy with this amp!Its mich cleaner now.
    I tried a 10 inch Jensen MOD 35 watt speaker with a plywood baffle,it added ALOT more bass to the amp BUT as crazy as it sounds i think i like the stock 8 inch speaker sound better.There is something very special about its sound.Its completely different than any other Fender amp i've used.
    My wife commented yesterday how great my playing sounds through the Vibro Champ.She said it never sounded so good!
    Coming from her that a BIG thing because she knows NOTHING about music or guitars,just a listener.I've had every thing from a 2-15 dual Showman to a pro reverb and solid state Fenders and old Inivox tube amps,this little amp is quite impressive.
    My intention is to order another Jensen MOD speaker and run two tens.One in this VC and one in a external cab OR put the two tens in a single cab and disconect the VC speaker when i use the 2-10 cab.

    I hope i'm not coming across as someone running you guys or not taking advice.I just like to explore things deeper than most and i'm NOT afraid to try different things.Thanks again

    I gotta add the amp is COMPLETELY QUIET with no odd noises or sounds since i installed the grounding cord.Thats why i'm not too quick to change anything out like caps.I like the sound as it is.
     
    Last edited: Aug 13, 2008
  20. Rick1114

    Rick1114 Member

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