67 BF Vibro Champ orig Fender Upgrades ?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by Groovey Records, Apr 17, 2008.

  1. Groovey Records

    Groovey Records Member

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    Let me say this place is amazing

    What I need is..

    I just got ahold of a mint 67 BF Vibro Champ, still has the 2 prong plug, a closet queen DEAD MINT clean as a shark. ! Speaker, Tubes, Cabinet, woopie doo !

    I don't have too tell you how good it sounds, you all KNOW what I am talking about.

    What my question is I heard before that the Late BF Champs had the PT upgraded by Fender as well as a few other upgrades from the Princeton Ofcourse this was done without changing the schematics and wiring diagrams.

    I understand that while this was an upgrade somethings were not brought up to speed for the heavier iron and might benifit from a few different Cathode Resistor values and what not being put into the circuit.

    If Anyone knows what I'm talking about please fill me in?:wink:

    So without pulling the chassis these are the part numbers and serial #'s I have.

    Vibro Champ Production # 28
    Chassis # A17120

    PT 022772/ 606-6-47

    OT 022905 / 606-6-38

    Speaker 8 EV -52 / 465-641

    Thanks to a great board and its Members I have already learned so Much!

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  2. mark norwine

    mark norwine Member

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    I don't know about "upgrade"....

    Vibro champs used the same PT as the princeton & Princeton reverb. Period. I don't think anything was upgraded anywhere.....it's simply the iron they chose to use.

    Huh? You've lost me there....

    I actually have no idea what you're asking...

    What exactly do you want to know?
     
  3. Jahn

    Jahn Listens to Johnny Marr, plays like John Denver Supporting Member

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    It looks to me like you have the same hardware as what a normal 60's Champ would have, not beefier or not wimpier. For instance, the OT for a 60's Champ would be 125A35A. and the equivalent is indeed 022905, so there you go - the same.
     
  4. wahfreak

    wahfreak Silver Supporting Member

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  5. doc

    doc Member

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    If its dead mint, I'd suggest leaving it alone and enjoying it as is. Change the caps at some point. Get another beat up Champ to mod. If you want to "beef it up", change the speaker to a Weber (a reversible mod). If you want to go farther, get a beat up Champ and put in the Area 51 fixed bias mod as well as the upgraded speaker.
     
  6. Groovey Records

    Groovey Records Member

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    YEP thats the ticket.

    So Thanks Wah FREAK !

    Mark Norwine, your always so helpful I hope I didn't mis phrase my question.

    What I guess I need to know is if this BF Vibro Champ I have is one of the latter ones John Phillips refers to and I included the Part and serial #'s to help confirm that it is a higher valued PT.

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  7. Jahn

    Jahn Listens to Johnny Marr, plays like John Denver Supporting Member

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    Doesn't look like your Vibro Champ is the Princeton Transformer type.

    Champ - [FONT=Arial, Helvetica, sans-serif]125A35A[/FONT][FONT=Arial, Helvetica, sans-serif]––>[/FONT][FONT=Arial, Helvetica, sans-serif]022905[/FONT]

    Princeton-

    [FONT=Arial, Helvetica, sans-serif]125A10B[/FONT][FONT=Arial, Helvetica, sans-serif]––>[/FONT][FONT=Arial, Helvetica, sans-serif]022913[/FONT]
     
  8. Groovey Records

    Groovey Records Member

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    I think these are the OT Numbers

    Anyone have the same info on the PT?

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  9. mark norwine

    mark norwine Member

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    PT was 125P1B ----> 022772 for Champ, Vibro Champ, Princeton & Princeton Reverb

    I'm unaware of any early champs having "smaller" or "different" iron.....
     
  10. Groovey Records

    Groovey Records Member

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    Mark Thanks, Everybody you're the Best

    Yeah thats the part number on my PT 022772 with 606-6-47 underneath.

    So where can I find out the values for that PT part #

    Anywhere I can date the parts?

    For your own info here is John Phillips post from the archives circa 2006.

    I miss that guy so much I read his old stuff. Thanks to John as well
    Begin Quote
    John Phillips
    Racket Scientist

    Join Date: Mar 2002
    Location: Scotland
    Posts: 13,372
    Your measurements are absolutely correct... it's Fender's design which isn't .

    No kidding.

    The stock 470-ohm cathode resistor is too low for that circuit, and results in the 6V6 running far too hot - not only over the maximum rating, but reduces the power available (clean) since the tube reaches forward clipping a long way before cutoff, which produces asymetrical clipping, and a rattier, fartier overdriven tone as well as less clean headroom.

    (IMO the most likely reason is that the earlier 4W Champs - Tweeds and the earliest BFs - had lower plate voltages, which makes the 470-ohm value correct. In about 1965 CBS/Fender decided to upgrade the power of the Champ, which they did simply by fitting a Princeton PT. This raises the B+ voltage far enough to give 6W output, but someone apparently wasn't paying enough attention, and they didn't change the value of the cathode resistor to keep the same operating point.)

    Biasing a single-ended amp correctly is about getting the operating point centered between cutoff and clipping so the waveform ends up symetrical (not to a particular power dissipation). You need a much higher cathode resistor value to achieve this with the high B+ in later Champs - typically 1K, but you could experiment with other values near that if you want.

    This will also take the cathode voltage up well above the 25V rating of the stock cap - usually into the low 30s - so you MUST replace this as well. I like to use a 50uF/50V cap since the bigger value compensates for the greater resistance.

    It's also a good idea to fit a screen resistor while you're in there - you may need larger than the 'traditional' 470-ohm here too, since the voltage drop across the OT primary is greater than in the higher-powered amps. (I would use 1K 2.5W or 3W wirewounds for both this and the cathode resistor).

    You should now find your Champ is louder, sweeter and more balanced sounding.
    __________________
    John P
    end quote
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  11. Dave C

    Dave C Gold Supporting Member

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  12. Groovey Records

    Groovey Records Member

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    Well Uncle Dave and Uncle Spot have come through !

    It Looks like this PT can put out from 6 - 18 watts ?

    Everybody else is right there is no other reference that I can find to earlier BF Champs having different iron. It certainly doesn't document any such thing in any schematics I can find

    But I will defer to John Phillips explanation as I quoted above. Or I am a Monkeys Uncle...

    So I am going to start another thread to address a mildley shocking issue.

    Thanks everyone and if you have anything to add please post I'll check back.

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