Resistor Question?

Discussion in 'Tube Audio' started by tube-a-lou, May 13, 2018.

  1. tube-a-lou

    tube-a-lou Super Member

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    4,424
    Hi all,
    I've been working on a 1953 Fender Deluxe amp and it had in the amp originally
    250K resistor's about five, I was able to find 240K and put them in. Now I found a stash
    of what looks like the original resistor's that Fender used way back when but they are
    270K's. What if any will a difference in sound be?


    5B3 (1).jpg
     

     

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  2. Dave451

    Dave451 AK Subscriber Subscriber

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    Not sure what the sound difference will be, if any, but the tolerance on equipment of this era was typically 10% for the resistors. If so, this means +/- 25K against the original value of 250K, or an 'in tolerance' span of 225K to 275K. The 240's are actually quite close, within 4%, so why change?
     
    Audiovet likes this.
  3. tube-a-lou

    tube-a-lou Super Member

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    The look of the amp, worth more if it has the original parts in it or close to it. The guitar
    world is different than the audio world!
     
  4. billyz

    billyz Active Member

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    240
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    The 270k for the plate loads will slightly increase gain and distortion. In the paraphase section it may cause a more unbalanced phase invertor, again more distortion.
     
  5. Bob

    Bob AK Subscriber Subscriber

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    measure the 240Ks, and the 270Ks, use the ones that are period correct for
    value preservation and closest to 250K. then document it for when you sell
    to someone more fussy than you about period correctness and will scream
    when he finds out it's not an original 250K.
     
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  6. Audiovet

    Audiovet Well-Known Member

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    And onother practical consideration: Consistency of tubes.

    I may have mentioned before that these days it is not seldom to find a spread in same number tubes of some '- 30% to + 30%. That makes a few percent change in resistance value of lesser consequence.
     
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  7. tube-a-lou

    tube-a-lou Super Member

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    If I go by the schematic the 250K's are by the first preamp tube and the second phase
    inverter tube both are 6SC7 tubes.
     
  8. nj pheonix

    nj pheonix AK Subscriber Subscriber

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    What did the originals look like?
     
  9. tube-a-lou

    tube-a-lou Super Member

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    Here's a picture I got off one of the sites. you could see them.


    fullsizeoutput_5e67.jpeg
     
  10. nj pheonix

    nj pheonix AK Subscriber Subscriber

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    I wouldn't have thunk it but apparently that's a dog size?:idea:
     
  11. tube-a-lou

    tube-a-lou Super Member

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    There really different looking resistor's, I know there not Allen Bradley.
     

     

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  12. nj pheonix

    nj pheonix AK Subscriber Subscriber

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    It's tough to see from the pic. They just look like carbon comps. How do they test.
    Being how noise and distortion aren't necessarily the enemy here, perhaps you should just leave them
     
  13. primosounds

    primosounds SE KT120 w/ 6J5G drivers. LCLC ps + 2 x 5ar4 Subscriber

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    If you are replacing the originals with carbon comps of the same wattage, only a techie who is a Fender junkie would realize that you switched from 250k to 240k. There should not be any difference in sound from the amp as you are within the tolerance factor. So, why worry? Be happy! regards.
     
  14. knockbill

    knockbill Addicted Member

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    Hey Lou,,, Its possible the stash of resistors you found are as old as the ones in the amp... Also very possible they are out of value as much as the originals... If the 240K and the 270K are both in value (which I doubt), they are more than 10% different... If it were me and I wanted to swap resistors, caps, etc in a vintage amp that had value because its untouched and has original parts,,, I would use modern, close tolerance parts and save the originals for a future owner,,, or just leave it alone, if you really want it exactly as Fender made it!!!!
     
  15. tube-a-lou

    tube-a-lou Super Member

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    True, the amp was restored in the late 80's and all the original 250K resistors were all
    changed to 220k resistor's. I found a few of those 270K resistors that look liked the ones
    Fender used back in the 50's I measured them and they measured between 269K to 280K.
    In the mean time I found Allen Bradley 240K's resistor's which are in there now. It's really
    a bit in my part of experimenting with amps and different sounds.
     
  16. crispycircuit

    crispycircuit AK Subscriber Subscriber

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    I have swapped out old parts for new shiny parts, only to find the old crappy parts have the mojo....mostly liking carbon comp resistors and old blue molded Ajax signal caps for Fenders. I've tried many electro's for the power supply dog house and didn't notice a difference... my 2 cents....
     
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  17. tube-a-lou

    tube-a-lou Super Member

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    Those Blue Molded and Yellow Astron's have a following more so for the Blue Molded they are
    said to hole up well though the years and sound good.
     
  18. billyz

    billyz Active Member

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    The Blue molded fender caps are almost always good. In fact, I don't think I have ever tested a bad one.
    The yellow Astron's are 50/50 though. Those Red paper label caps are almost always bad .
    The dominoe mica cap is almost always good and very good sounding.
    I don't think the value is hurt too badly replacing Carbon Comp resistors with Carbon Comp, even though the newer ones are smaller than those early ones in your amp. If you want them to look closer to the original ones you could use 1 watt. The carbon comp do sound the best though if they are not noisy.
    Wholesale replacement with metal film and orange drop caps does hurt the value and tone quite a bit.
     
  19. triode17

    triode17 Well-Known Member

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    973
    You didn't specify which model board it has. So I have to assume it's either the 5A3, 5B3 or 5C3 because after that, they re-designed the amp and used different tubes and therefore different parts.
    The plate resistors in a phase inverter are somewhat critical as to their matching abilities. Looking at your photo and following the Fender assembly diagram, those two resistors look like they have no tolerance (4th) band. So they are +/-20% or 200-300k Ohms. I would use the 240k's you have but hand match them using an ohmmeter to as close as possible. Even if the parts were 5%, that would still be 238-262K Ohms, so the 240ks would work as long as they are at least 238k. This won't adversely affect the sound.
     

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