1967 Vibro-Champ

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by trisonic, Jun 26, 2003.


  1. trisonic

    trisonic Member

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    My '67 Vibro-Champ is sick and needs a 500K mile service.

    While I am at it should I have any mods performed on it? I know it's a classic but there are zillions of these around.

    So far as I know it is bog-standard but it has always sounded rather "shrill" to me at full wack.

    1. I'd like to keep the tremelo (it's the only one I've got)

    2. Anyone know a good amp tech in Central New Jersey (nr Westfield).

    Thanks upfront for advice.

    Pete.
     
  2. John Phillips

    John Phillips Member

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    It will need a filter cap job done if it hasn't been already, and a 3-wire power cord fitted (don't even think about not having this done if it doesn't have one).

    IMO you should also have it rebiased correctly - later BF and all SF Champs are biased wrong from the factory, surprisingly - this runs the 6V6 over-hot and makes the distortion sound bad (IMO); although the usual complaint is farty bass distortion. Biasing correctly gives more clean headroom, a tighter, smoother distortion and better tube life.

    To do this, you need to replace the 470-ohm cathode resistor with a 1K (5W wirewound is best) or thereabouts - there's a small range of variation, but the right value will be between 820 ohms and 1.2K, and 1K is a good guess. You MUST also replace the cathode bypass cap with a 50V rated one if you do this since the bias voltage goes up to well over the 25V rating of the existing cap (usually to about 30V). I double the value to 50uF too to maintain the same low-end response.

    While you're in there, fit a screen-grid resistor as well, which Fender also skipped. The usual Fender value of 470 also isn't enough here, since the voltage drop across the (relatively high imedance) OT primary is higher than usual. 1K (2 or 5W wirewound) is enough here too.

    Personally, I wouldn't do anything else...
     
  3. trisonic

    trisonic Member

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    Thanks, John. I had hoped you would step forward!
    Yes it definitely does fart out and the other distortion factor is maybe the shrillness I hear.

    You ever thought of emigration over here????????

    Otherwise can someone step forward and recommend a tech to a relative newcomer to New Jersey?


    Pete.
     
  4. John Phillips

    John Phillips Member

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    You could try John Frondelli - he's in New York City not New Jersey, but he's really good. He posts on the Fender forum as jrfrond, and although I've of course never had anything done by him personally it's obvious he knows what he's talking about.

    His email is jrfrond@dbmproaudio.com. I'm sure he won''t mind me posting that here since it's his contact email from the FDP.
     
  5. trisonic

    trisonic Member

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    Thanks John.
    I'll send Mr. Frondelli an email and if we can't hook up maybe he'll be able to suggest someone good on this side of the Hudson.

    BTW I tried to register with that forum but I always end up going around in circles until I get p---ed off and leave!!

    Thanks, again. Pete

    (I'll report back at a later date)
     
  6. Ron

    Ron Supporting Member

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    A useful mod is to replace the 1M-ohm volume control pot with a 1M-ohm pot with a push-pull switch on the back. You can use the switch section to either bypass the EQ with a cap, or lift the mid resistor. Either way, you can turn the Vibro Champ into a Vibro Tweed Champ instantly with a tug on the volume control.

    Review the schematics to see what I'm talking about.

    Ron
    King Amplifier Co.
     
  7. trisonic

    trisonic Member

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    Thanks, Ron. Sorry it took so long to acknowledge!
    Pete
     
  8. FlyingVBlues

    FlyingVBlues Gold Supporting Member

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    Pete,

    Try Dave Hirsh in Whippany.... his guitar tech, Bill Baker, is also very good.

    Dave's Sound Repair
    622 Rt. 10
    Whippany, N.J. 07981
    973-386-5840

    http://www.gti.net/junebug/dave/

    If Dave isn't available try Dennis Kager at Central Jersey Music in Edison or JImmy Somma in Sommerville.

    Dennis Kager
    Central Jersey Music
    1627 Rt 27
    Edison, NJ 08817
    732-572-1911

    Jimmy Somma
    Sommatone Guitar & Amplifier Repair -- Sommatone@aol.com
    Somerville, NJ 08876
    908-704-0041

    All 3 are a fairly short drive from Westfield and are first rate amp techs.

    FVB
     
  9. trisonic

    trisonic Member

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    Thanks, FVB!

    Pete
     

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