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Here's a stumper: Differences between 6G2 & 6G2-A?

Discussion in 'Amp Central Station' started by kosmonautmayhem, Nov 8, 2010.

  1. kosmonautmayhem

    kosmonautmayhem Tele-Meister

    432
    Jan 11, 2010
    Chicago
    Brown era Princeton:

    Any one out there know the differences, if any?

    Here's a pic from my black, '64 6G2 to get things started. I've only ever seen the "A" hand written next to 6G2 on one or two earlier brown Princetons - I believe they were 62s.
     

    Attached Files:


  2. RubyRae

    RubyRae Friend of Leo's

    Age:
    42
    Dec 8, 2009
    Cincinnati
    My guess is no difference, but who knows. Interesting that it was only handwritten, and on very few models. It would have guessed when you said that that possibly on '64models during the transition, but strange that they were on 62's.
    Cool though definitely, and yet another obscure inconsistancy in the wonderful world of vintage Fender tube charts.
     

  3. mr.danny

    mr.danny Former Member

    Jun 16, 2010
    Milwaukee
    Tube chart weirdness: Even though from 57 - 60 Tremolux was 5G9 circuit, I've spoken to several people with extensive experience who've never seen it on a tube chart. It's always 5F9 or 5F9a pencilled in.
     

  4. meyekel

    meyekel Tele-Holic

    755
    Oct 3, 2006
    Denver
    I have a 6G2A that is from 1962. I don't know any circuit changes but the big difference in the amp I have is it has an Alnico Oxford speaker as opposed to the ceramic. Please forgive the JJ bottles, they were quickly dispatched in favor of some NOS Brimars.

    [​IMG]
     

  5. JohnnyCrash

    JohnnyCrash Doctor of Teleocity Silver Supporter

    Mar 12, 2005
    Fullerton, CA
    If you two take photos of the guts, we can look at the circuit and figure out if there are any differences between your 6G2 and meyekel's 6G2-A...
     

  6. ThermionicScott

    ThermionicScott Poster Extraordinaire

    Age:
    37
    Dec 3, 2005
    SW CR IA US NA PE
    I wonder if 6G2A was a really short-lived change (in '62 or thereabouts) that Fender decided not to stick with. I'm intrigued as to what the difference was, as well!

    - Scott

    P.S. That reminds me, I've got a friend with a brown Princeton. Maybe he'll let me inspect it...
     

  7. RubyRae

    RubyRae Friend of Leo's

    Age:
    42
    Dec 8, 2009
    Cincinnati
    That is exactly what I was thinking, that they possibly penciled in 'a' if there was an alnico speaker...but who the heck knows. I just love these amps, and envy you dudes that have em. :cool:
     

  8. meyekel

    meyekel Tele-Holic

    755
    Oct 3, 2006
    Denver
    I'd be down with some gut shot comparisons. I have no clue what I am looking at but I can post the photos and let the experts chime in.

    [​IMG]

    [​IMG]

    [​IMG]

    [​IMG]

    [​IMG]
     

  9. ThermionicScott

    ThermionicScott Poster Extraordinaire

    Age:
    37
    Dec 3, 2005
    SW CR IA US NA PE
    Nice pictures, meyekel! I'll scrutinize them some more when I get home from work. :cool:

    - Scott
     

  10. kosmonautmayhem

    kosmonautmayhem Tele-Meister

    432
    Jan 11, 2010
    Chicago
    Show off yer GUTS!!! nice.

    Alright I'm back! Thats a really great theory about the Alnico speaker! I have no idea what the stock speaker was in my amp. It came to me with a replacement JBL which I swapped for a Weber 10F150, light dope. Sounds out of this world. My guts for comparison, good sirs...
     

    Attached Files:


  11. kosmonautmayhem

    kosmonautmayhem Tele-Meister

    432
    Jan 11, 2010
    Chicago
    and some more...

    Lets get out the microscopes!

    kM
     

    Attached Files:


  12. ThermionicScott

    ThermionicScott Poster Extraordinaire

    Age:
    37
    Dec 3, 2005
    SW CR IA US NA PE
    So the only thing that popped out at me on meyekel's amp is that the tremolo stage has a 100uF cathode bypass cap, not the 25uF indicated on the schematic. Of course, it could be an incorrect replacement part, too. (Not one that will harm anything though!)

    - Scott
     

  13. kosmonautmayhem

    kosmonautmayhem Tele-Meister

    432
    Jan 11, 2010
    Chicago
    Good eye, Scott! Would this make any audible difference? I guess there could be a lot of reasons there's a 100uF cap there instead of 25uF. I've read "stories" how Leo would tinker with small changes not noted in schematics...could also be a replacement cap from a repair but I have to doubt that notion - meyekel's '62 looks completely original. Could have possibly been a factory mistake or a cap that worked for the situation, given they ran out of 25uF?

    This is becoming an intriguing thread!

    Anyone know what kind of speakers came stock with the later model 6G2s compared to the early ones? Were they all Alnico or did they use Ceramics, same manufacturers? Was there a few years of consistency regarding speakers?
     

  14. smokerjoe34

    smokerjoe34 Tele-Holic

    697
    Mar 25, 2009
    Enid,Oklahoma
    My 62' Princeton also has the Alnico speaker and the A penciled in so the A must stand for the Alnico speaker difference ??
     

  15. Dave Hopping

    Dave Hopping Friend of Leo's

    Jun 28, 2006
    Aurora,Colorado
    My 11/61 Princeton also has the letter A handwritten on the tube chart.The speaker looks identical to Myekel's and on the side of that big metal thingie on the back of the speaker in the center is stamped 10JB-14,with the numbers 465-123 underneath.
     

  16. ThermionicScott

    ThermionicScott Poster Extraordinaire

    Age:
    37
    Dec 3, 2005
    SW CR IA US NA PE
    Well, that cap serves to keep the cathode voltage constant when a signal is applied. (When the cathode voltage is allowed to "float", it'll wiggle with the signal and reduce the gain of the stage.) According to the RCA book, with a 300V source, a 220K plate resistor, and a 3100-ohm cathode resistor (close enough to the 3300 in the Princeton), a 2.1uF capacitor is sufficient to do the job. So, Fender was already using 10 times that value! :lol: Could just be that they ran low on 25uF caps that day, and it didn't hurt anything to pop in a 100uF.

    I'm having a little trouble making out the values in your amp, kosmonaut. Could you take some closer pics of the capacitors, and the bias circuit (the little board that's off by its lonesome)? Looks like someone "liberated" a lot of your blue Mallory signal caps. :(

    - Scott
     

  17. kosmonautmayhem

    kosmonautmayhem Tele-Meister

    432
    Jan 11, 2010
    Chicago
    Dave, SmokerJoe - thanks for weighing in on the issue! I think Alnico is a good strong theory for the penciled "A".
    --Anyone want to weigh in on their later (63-64) 6G2 speakers?

    Scott, Here are a few more pics I have on hand. I must remove the chassis to take another group of pics to get all cap values up close. I can do this tonite. You really think someone liberated signal caps from my board!?!? I guess it wouldn't surprise me. I see meyekel's are all blue. I've never actually seen the little blue molded caps before!
    Anyone know if Fender was using these kind of chocolate drops in 64? :/
     

    Attached Files:


  18. kosmonautmayhem

    kosmonautmayhem Tele-Meister

    432
    Jan 11, 2010
    Chicago
    and a few more...
     

    Attached Files:


  19. meyekel

    meyekel Tele-Holic

    755
    Oct 3, 2006
    Denver
    Hmmmm, the alnico speaker theory is gaining some plausibility. I know that Fender was starting to change over to mostly ceramic speakers from the tweed to BF era amps. It sounds like it would be in line with Leo's principle of using up the remaining stock and then switching to the newer components during a production run. Here's a few iron shots to get closer to a date for the 6G2a. Looks like the tail end of 1961.

    [​IMG]

    [​IMG]
     

  20. mr.danny

    mr.danny Former Member

    Jun 16, 2010
    Milwaukee
    I'm no expert on this but I really doubt "a" is for "alnico".
    They used "a" for circuit revisions in the 50's occasionally (ie: 5F9a)
     

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