1960 6G4 Super "Missing" 220K Trem Resistors

Discussion in 'Amp Tech Center' started by Gibsonsmu, Jul 16, 2018.

  1. Gibsonsmu

    Gibsonsmu Tele-Holic

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    I recently acquired a mid (July) 1960 Super, 6G4 amp (5 pre amp tubes). I was comparing the board to a a early "center volume" circuit and it is identical except for two 220K resistors in the trem circuit that are "missing" relative to the other amp I compared to and the schematic. At first I thought it was a mod but then I found another one (center volume knob as well) that had the same set up as mine. Also, there are no eyelets so it appears deliberate. Any idea what that might be and / or what difference that would make. Obviously they were experimenting a lot with the harmonic tremolo in this time period. Any thoughts?

    6G4 Schematic - Noted.png 6g4 Layout Pointed.png 6G4 Board EB.png 1959 With 220K.png 1960 Center Volume Like EB.png
     
  2. Andy B

    Andy B Tele-Afflicted Gold Supporter

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    The two 220K resistors are the mixing resistors where the preamps for each of the 2 channels combine. The are put there to isolate the signal of each channel for each other.
     
  3. Snfoilhat

    Snfoilhat Tele-Afflicted

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    You'll want to talk to the folks in this thread. http://www.tdpri.com/threads/exploring-fenders-harmonic-tremolo.791406/

    Those 220K resistors are part of the low-pass or band-pass or high-pass filter system that sends signal into either of the two triodes of V4 depending on frequency, which is the basis of the 6G* trem system. Those filters underwent a few changes and can work (with different results) in few different configurations.

    There are three channels in this amp, Normal, and the two harmonic trem channels which are modulated out of phase with one another by the LFO. Their mixing resistors are the two 470K and the one 1M which are located nearby, but aren't the 220Ks you're talking about.
     
    Last edited: Jul 16, 2018
  4. schmee

    schmee Poster Extraordinaire

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    That's what I thought....? But I dont see the usual wires bridging over there. Unless they are under the board...
     
  5. Gibsonsmu

    Gibsonsmu Tele-Holic

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    Yeah, I looked at the other thread but wasn't able to piece together what the elimination of these would do

    @clintj
     
  6. Wally

    Wally Telefied Ad Free Member

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    That early circuit is NOT the same as the later circuit. There is an added stage in that trem circuit in the later amps.
     
  7. Gibsonsmu

    Gibsonsmu Tele-Holic

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    Indeed they are very different, and it looks like even in the early circuit they were tweaking, just wish I knew what the tweak was!
     
  8. moosie

    moosie Doctor of Teleocity Silver Supporter

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    Read through Leo's 4-triode patent application. There's a wealth of information in it, including a description of each component and it's function.
     

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  9. ocduff

    ocduff TDPRI Member

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    That's one of my favorite amp designs. Dark chocolatey richness. But I've heard ones that sound amazing and some that sounded like dook.
     
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