Screen Resistor mod

Discussion in 'Amp Tech Center' started by ce24, Sep 30, 2019.

  1. ce24

    ce24 Poster Extraordinaire

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    upload_2019-9-30_7-40-36.png so the original has the B+2 to 6v6 socket going to pin 4. This mod shows it moved to pin 1 with the resistor going from pin1 to pin 4 which is now blank after the move. My question is, is it necessary to rewire the B+2 to pin one? Then the resistors of course from 1 to 4.
    Thanks for any replies
     
  2. Wally

    Wally Telefied Ad Free Member

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    The only reason I can see for using pins 1&6 as they do above rather than the vintage Fender manner of using pin1 for the control grid stopper intact and the pin 6 as a contact point for the screen grid resistor is that the screen grid stopper is not stack above the control grid stopper in the ‘edge’ method. The Edge approach allow better access to the control grid stopper in case it blows.
     
  3. ce24

    ce24 Poster Extraordinaire

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    Do you mean pin 4? You lost me....lol
     
  4. Nickfl

    Nickfl Tele-Afflicted

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    Pin one isn't connected to anything internally (except on a metal tube where it's connected to the metal shell), it's just a convenient landing point for the extra component. You can just hang the resistor off pin 4 if you want. It won't be quite as sturdy, but electrically B+2 > resistor > pin 4 is what matters.

    Pin 6 is the same thing, no internal connection, it's just used as physical support for the grid stopper.
     
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  5. Wally

    Wally Telefied Ad Free Member

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    No, I mean to say that pins 1 and 6 are being used as contact points since they hav no internal connections in a 6V6/6L6 beam tetrode tube. So, Fender began using those pins as contact points for the voltage to the screen grid on pin 4 and the control grid on pin 5. The vintage arrangement was to take the bias voltage feed to pin 1. The control grid stopper resistor was than spanned across the socket to the control grid pin 5. The screen grid voltage was contacted on pin 6 from where the screen grid resistor spanned across the socket..and above that control grid stopper....to the screen grid pin4.
    This edge amp has simply changed the contact points. I like the Edge arrangement.
     
  6. ce24

    ce24 Poster Extraordinaire

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    Thanks Wally and nickfl....so I CAN just add the resistor on pin 1 and 4 without moving other wires? My lack of knowledge is on display here! Lol
     
  7. Snfoilhat

    Snfoilhat Tele-Afflicted

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    The resistor has to be in series with the voltage supply. If your B+2 connection goes directly to pin 4 now, then adding a resistor from pin 1 to pin 4 will not do anything. If you begin with a stock 5E3, you have to move a wire.
     
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  8. ce24

    ce24 Poster Extraordinaire

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    That's what I need....thanks guys..... My mechanical skill far surpasses my electronics skills.
     
  9. ce24

    ce24 Poster Extraordinaire

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    LAST question. This is suppose to prolong tube life. If it’s a negligible extension of tube life it’s not worth the effort. I’ve had this amp for over ten years since I built it. Tube life doesn’t seem to a big issue for it.....I’m just an insatiable tinkerer. Does this mod do anything other than extend tube life?
    Again thanks for the replies.
     
  10. Wally

    Wally Telefied Ad Free Member

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    Knowing the pinout for tubes is valuable info. For instance, in amps that can run either a beam tetrode or a true pentode, pin 1 cannot be used for a contact point for any source voltage because pin 1 is the suppressor grid in a pentode and is usually tied to the cathode and grounded. In modding a Fender with typical wiring, that pin 1 has to be cleared for grounding to accommodate the pentode...say an EL34. The control grid resistor Contact point on P1 vintage Fender circuit has to be moved moved off of pin 1.

    http://www.valvewizard.co.uk/gridstopper.html
     
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  11. FenderLover

    FenderLover Friend of Leo's

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    I'd submit that it is a safety measure, and by today's standard a good idea, but not completely necessary. If you use it for gigging, why not, but otherwise my 1955 Deluxe is still going strong on the tubes I got it with 25 years ago. A 470K grid stopper on the phase inverter is the single best mod one can make to the 5E3 for performance, IMO.
     
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  12. Wally

    Wally Telefied Ad Free Member

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    On which grid?
     
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  13. FenderLover

    FenderLover Friend of Leo's

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    CE24 refers to the output screen grids, me too
     
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  14. Wally

    Wally Telefied Ad Free Member

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    I apologize for my initial question since it had no reason to be asked because you were referring to the phase inverter of the 5E3, which has only control grids...no screens.

    So, now my question is to which control grid did you apply this 470kohm resistor?
     
  15. FenderLover

    FenderLover Friend of Leo's

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    I should have started a new paragraph instead of rambling on, but yeah, 470K on the phase inverter grid is the primo improvement.
     
  16. peteb

    peteb Friend of Leo's

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    if its the PI tube getting the screen resistor and / or grid resistor, then the pins are not 1,4,5,6.


    i thought this might help:




    the screen on the 6v6 is pin 4. disconnect the wire from pin 4 and reconnect the wire to pin 6. the screen grid resistor then gets connected between pins 4 and 6.


    the grid of the 6v6 is pin 5. what is typically done is disconnect the wire from pin 5 and move it to pin 1. the grid stopper resistor is then added between pins 5 and 1.



    the edge 5E3 may use different pins. I was just describing how it usually gets done.
     
  17. Wally

    Wally Telefied Ad Free Member

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    Fwiw,all of that has been covered way back early in this thread. Re: ..”the grid of the 6V6 is pin 5”....without someone understanding which grid that pin is attached to, they will not know that that particular grid is the control grid where the bias voltage is applied.

    And yes...perhaps Fender Lover and I should not have ventured away from the original thread’s subject. fender Lover, it has finally dawned upon me that there is only one control grid on the phase inverter since that function is covered by the second triode in that 12AX7.
    I’ll suss it out.
     
    Last edited: Sep 30, 2019
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  18. ce24

    ce24 Poster Extraordinaire

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    It’s all good my friends....I have the information I asked through all of your generous replies. I’ve settled that I really have no need for the screen resistor 470k mod on my 6v6 tubes, pin 1 to pin 4. I’m humbled by all your knowledge and my lack there of!
    Cheers
    ce24
     
  19. Wally

    Wally Telefied Ad Free Member

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    Ce24, just to keep things straight... that screen grid stopper resistor on the power tube would be a 470ohm resistor. The 470K ohm resistor that came up in Fender Lover’s post is placed on the cathode phase inverter control grid. Sorry for the diversion.
     
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  20. ce24

    ce24 Poster Extraordinaire

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    Thanks Wally, I noticed that when you caught my mistake on the grid stopper. It’s all in the details isn’t it? Lol....I referenced the wrong value again on my screen resistor question. I learn well, but sometimes very slowly!
     
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