69 Super Reverb ... Possible AB763 circuit?

Discussion in 'Amps and Cabs' started by themusicboxstudios, Jul 11, 2006.


  1. themusicboxstudios

    themusicboxstudios Member

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    I got this from the seller who claims that the amp has the AB763 circuit accoring to his tech.

    1. Tube chart is there but is not complete. Model # is missing.

    2. Trans 1 = F022T98 & 606852 Trans 2 = 0222699 & 606-9-02 Trans 3 = 022855 & 606846
    There is also a component near the Preamp tubes on the chasis = 022921 & 606-9-02

    3. Speakers are 100% original #137 6905

    is this possible?


    he's offering this and a mint matching Princton Reverb which he claims to have the AA1164 circuit w/ the following info

    Princeton Reverb #s

    1. Model AA764

    2. Trans 1 = F022T72 & 606834 Trans 2= 022913 & 606-8-18

    3. Speaker Original (has a sticker on it = 023010 & 465-919 &104J-5

    What do you guys think is a fair price for both of these amps?

    thanks, jon
     
  2. Blue Strat

    Blue Strat Member

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    I doubt there were any AB763s made in 1969. I don't "do" transformer codes, that's what online references are for. If the amp is a '69, it probably won't have 1966 or earlier transformers.

    Ask the seller if the amp was modified to AB763 specs. If the tech can ID a 763 he should be able to tell you if it's been modified. If it has been modded, pay the 1969 price (can't remember off the top of my head what circuit number that is, maybe 858?) plus a small premium for the conversion.
     
  3. Swarty

    Swarty Member

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    No chance IMO. By mid '68 the Super Reverbs had the worst of all the CBS era "enhancements"... the 150ohm cathode resistors, the '002 bleeder caps and the changes to the PI circuit and bias control. The AB763 tube chart lasted well past these circuit changes, even with the AB763 chart you need to open them up and look.
     
  4. JustAHack

    JustAHack Member

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    If the seller is willing to allow you to (CAREFULLY, TOUCHING NOTHING INSIDE) slide the chassis out just a bit to "peek", or do it for you, it should look something like this. It's the guts of my early '68 Super Reverb w/AB763 circuit.

    To narrow it down to one spot on the board, here's one indication of a Blackface circuit. If you look between the two big fat blue Mallory output coupling capacitors at the far left of the board, you'll see two small bias splitter resistors arranged in a "V". The later circuits don't have this "V". They just have the right half of the "V", a single resistor. I don't know what this means specifically, but it's one spot to look at if you can.

    Note: I'm not an amp tech or anything - I'm just going by books and chassis layouts I read when I was shopping for my Super. I got to peek inside first, but my amp tech confirmed later. Others on this board would be much more qualified to judge, but pictures of the insides of these amps are hard to find online, and I thought it might help you. I believe the Princeton would have the same arrangement of caps and resistors in this spot.


    [​IMG]
     
  5. themusicboxstudios

    themusicboxstudios Member

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    update from seller:

    "my tech is 99.9% sure that this has the manual bias which would indicate that this has the BF circuit. Plus as he was telling me earlier today when I called him...the difference between the two circuits is minimal and it would be a minor mod to make it a BF circuit should anybody really want to. BTW the cap job was done with Sprague's. "

    any thoughts on this?
     
  6. Blue Strat

    Blue Strat Member

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    Even the later "bias balance" versions have a bias pot in the same location and might appear to be "true bias" to a novice. If his tech doesn't know by looking at the bias control whether it's true bias for sure, he's a rank amateur and I wouldn't trust anything being said about this amp.

    See if you can get an inside photo of the chassis including the power tube and bias control areas (this is crucial for this assessment).

    Otherwise, consider it a later circuit (most of which don't sound as good as blackfaces even after the typical circuit changes) and pay accordingly.
     
  7. themusicboxstudios

    themusicboxstudios Member

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    thanks so much for your help ... i think i'm gonna pass ... i just don't have the kind of money to take a chance ... i'd rather wait for a blackface.

    thanks, jon
     
  8. JoeYello

    JoeYello Member

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    I have a 68 with the piping around the speaker grill. The amp was in bad shape when I got it so I printed a schematic that I got through the Ampwares site (forget what they call the tech part). I was looking to replace all the electrolytic caps. As I tried to match up the circuit I realized I had the AB763 circuit. After some repairs I have a great sounding Super Reverb! I believe that this may have been a transition year as I have heard other similar stories to mine.
     
  9. clunk

    clunk Member

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    Based on all i have read, 68 was the transition year for most amps that went away from the ab763 circuit. I doubt if there were hardly any by 69.

    Clunk
     
  10. Mastervolume

    Mastervolume Member

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    I am sure that it is not the 763 as well.
     
  11. Blue Strat

    Blue Strat Member

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    Fenders with the "drip edge" around the grill cloth most often have blackface circuits inside.
     
  12. Wakarusa

    Wakarusa Member

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    Have to disagree Mike. The drip edge silverface cosmetics first appear in late '67 and run through '69. For Super Reverbs, the "CBS" circuit with cathode resistors, bias balance, and 2nF caps grid to cathode start showing up in mid '68. The circuit "date" is May of '68, so there's a transition period, but by '69 every SR I've seen has the AB568 circuit.

    Similar story for the for the Princeton (and Champs for that matter). Even though they still get stamped/referred to as AA1164 and AA764 respectively, in mid '68 they picked up the grid-cathode caps (neither had a bias adjust so no level vs balance shenanigans here).

    The good news is that, as far as I can tell, the transformers stayed the same, so it's just a few minutes with your handy Xcelite 378M and a soldering iron to put the circuit back to AB763 (or published AA1164 in the case of the Princeton) specs. On rare occasions the lead dress needs to be corrected (which is why they started throwing those caps in ;))
     
  13. Blue Strat

    Blue Strat Member

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    Interesting, I don't think I've seen a drip edge past '68.

    In any event, the bottom line is ALWAYS what's inside. Always check or have someone who knows what he's looking at check for you.
     
  14. ampholic

    ampholic Member

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    If it is a GZ34 rectifier it is the AB763 circuit. If it is a 5U4 it is not.
     
  15. Blue Strat

    Blue Strat Member

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    Yes, but the only way to know if it's the correct rectifier (either will work in any circuit variation) is to pull the chassis and measure the B+ voltage.
     
  16. Wakarusa

    Wakarusa Member

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    For your viewing pleasure, a '69 drip edge VibroChamp :)

    [​IMG]
     

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