Tone controls

Discussion in 'Amp Tech Center' started by ce24, Dec 5, 2018.

  1. ce24

    ce24 Poster Extraordinaire

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    So it seems the tone controls on my 69 NV Princeton have no effect .. this is a new development .... It has had a complete service by Wally just recently...... Tone is great, plays well. I play it at about 5 on the vol. Any ideas tdpri?
    Cheers
    Ce24
     
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  2. peteb

    peteb Friend of Leo's

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    Put an ohm meter across them and turn them. That would be the first step
     
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  3. uriah1

    uriah1 Telefied Ad Free Member

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    Odd. You may ask Wally. did you have tone stack mods. Pop the hood open, perhaps a dropped piece of solder or dangling lead from shipping travel, or other.
    wish you luck.
     
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  4. robrob

    robrob Poster Extraordinaire Ad Free Member

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    If the 6.8k mid resistor's ground connection is broken the tone stack is lifted. This is how a raw switch works. Measure the resistance from the bass pot's output (connected to the mid resistor) to ground. It should measure 6.8k. It's probably an open connection.
     
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  5. ce24

    ce24 Poster Extraordinaire

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    Thanks guys... I'm home with with a sore throat and can check it all today.... Will report back..
     
    Last edited: Dec 6, 2018
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  6. Wally

    Wally Telefied Ad Free Member

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    Iirc, I replaced that 6.8k midrange resistor with a larger value to pump up the mids. Hopefully that connection did not go bad. Ce24, if the amp has gotten really hot and lively, what Rob describes may be exactly the problem.
     
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  7. ce24

    ce24 Poster Extraordinaire

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    Ok here we go....no broken or bad solder joints.
    MM OHM setting 2k.

    Wally replaced the 6.8 resistor with a 220 ohm to boost the mids.
    Oddities
    Measuring the 220 bass pot to ground gives me no reading.... However when I measure across the lugs i get a 0 reading on 10 and a .015 at 0 on the treble pot and 0 to .029 on the bass pot going from 0-10

    When i probe across the 220bass pot resistor I get no reading....
     
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  8. aerhed

    aerhed Friend of Leo's

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    220?
     
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  9. ce24

    ce24 Poster Extraordinaire

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    Yep...red red yellow gold. Suppose to boost the mids.
     
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  10. ce24

    ce24 Poster Extraordinaire

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    Can a too hot bias cause this?
     
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  11. ce24

    ce24 Poster Extraordinaire

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    I'm getting some movement. I checked bias with my Eurotubes bias plug... The simple one and it showed 20ma so I boosted it to 24.4-5 and I'm getting some variance
     
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  12. Lynxtrap

    Lynxtrap Tele-Holic

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    220 ohms to ground? Seems like close to nothing to me...
     
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  13. jhundt

    jhundt Doctor of Teleocity

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    if that is in fact a 220-ohm resistor, that would explain the lack of action on the tone controls. Perhaps it was inadvertently placed instead of a 22k (which is what a red-red-yellow should be) why don't you check the value again with your meter?
     
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  14. clintj

    clintj Friend of Leo's

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    You're on the wrong range. Trying to measure a 22k resistor, let alone a tone pot (typically 250k to 1m are used) will read off scale high assuming the meter will recognize it at all. Start on the highest range of your meter and work down until you get useful readings.
     
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  15. ce24

    ce24 Poster Extraordinaire

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    Thanks Clintj.... Will do.....
     
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  16. Wally

    Wally Telefied Ad Free Member

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    Ce24, the work order shows that I put a 22k ohm reisitor in place of the 6.8k ohm midrange resistor. If that resistor is not red, red, orange then I made a mistake. However, the amp didn’t sound as if I did make a mistake in the selection of the resistor when I shipped it off....and the tone stack has worked these many months....what 8 or 9 months? What is the date on the work order. Check my solder joints of that resistor. Measure it with one end lifted.
    If in fact I did make a mistake in the selection of the resistor...the repair is on me. Ship it back..I’ll fix it, and throw in a primo NOS tube as compensation for your shipping costs, and ship it back to you at my expense.
     
    Last edited: Dec 8, 2018
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  17. ce24

    ce24 Poster Extraordinaire

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    IMG_20181208_122432595.jpg here is a pic on the right, the resistor that was put in. I changed it out and put the original 6.8 back in and all I good in the universe.... Thank you so much fellow forumites....much appreciated!
    Cheers
    Ce24
     
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  18. ce24

    ce24 Poster Extraordinaire

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    Thanks for such a generous offer. I have skills to revert it back to the originsal 6.8. plus I've learned a thing or two. Well worth process.
    I have done the work and now the amp is fine.
    Thanks Wally!!
     
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  19. Bluey

    Bluey Tele-Meister

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    Wow..wish you could get such service & honesty in the rest of the world!!!
     
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  20. Wally

    Wally Telefied Ad Free Member

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    Well, it seems I did make an error....proving once again I am a mere human, right? I picked up a 220K resistor....duh! Serious midrange was probably causing the movement of the bass and treble controls to be obscured.
    Note to self: double check everything.
     
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