Artificial Heater Center Tap Resistors?

Discussion in 'Amp Tech Center' started by James Knox, Aug 6, 2020.

  1. James Knox

    James Knox Tele-Meister Ad Free Member

    Posts:
    474
    Joined:
    Aug 13, 2003
    Location:
    Phoenix
    This Hammond 290CAX has no Heater Center Tap so I gotta hang a couple resistors. I know 100ohm is the normal value.

    Because I do not have any on hand right now, what other values could I use?

    Really don’t want to hold up my build and pay shipping on a few resistors.

    Peace,
    James
     
  2. ThermionicScott

    ThermionicScott Poster Extraordinaire

    Age:
    40
    Posts:
    5,978
    Joined:
    Dec 3, 2005
    Location:
    CID
    Whatcha got on hand? Fender used a 100 ohm pot for their "hum adjust" knob, which would be like two 50 ohm resistors. I would imagine anything between 50-250 ohms would do the job.
     
    the fatch and James Knox like this.
  3. Lowerleftcoast

    Lowerleftcoast Tele-Afflicted

    Posts:
    1,712
    Joined:
    Dec 30, 2019
    Location:
    california
    You should stay lowish. No higher than ~500 ohm I would think. It is usually suggested 100-220. Hum dinger pot is usually 500ohm.
     
    James Knox likes this.
  4. sudogeek

    sudogeek Tele-Meister

    Posts:
    189
    Joined:
    Sep 9, 2016
    Location:
    Palm Beach FL
    Use your 100 ohm pot as a humdinger. You can hang an arbitrary resistor (25-100 ohm) off the center lug to ground if you want. Or, ground the heaters (or humdinger pot) to the cathode resistor (for a cathode biased amp), elevating the heaters to further reduce hum.
     
    James Knox likes this.
  5. tubelectron

    tubelectron Tele-Afflicted

    Posts:
    1,331
    Joined:
    Nov 25, 2010
    Location:
    France
    @James Knox,

    If it was me, and if the amp has gain or is powerful, I would use a molded track pot wit 220R or 470R value (I often use 220R) for a precise hum balance adjustment.

    If the amp gain is moderate (like below), I would use a pair of 100R 2W. In both case and for better efficiency in heater hum cancelling, place the Rs or the Pot accross the input preamp tube, and not on the pilot light à la Fender :

    [​IMG]

    But it's me, OK ? :D
     
    James Knox likes this.
  6. James Knox

    James Knox Tele-Meister Ad Free Member

    Posts:
    474
    Joined:
    Aug 13, 2003
    Location:
    Phoenix
    Ok, thanks for the input Brothers! Gonna just order some 100R’s...

    ...and study Humdingers!
     
  7. gusfinley

    gusfinley Tele-Afflicted

    Posts:
    1,148
    Joined:
    Jun 11, 2014
    Location:
    SLC, UT
    Get 1% resistors!

    The humdinger pot is to find the balance point between the two haves of the pot. With modern 1% resistors there is no need to find the balance of match resistors!

    I once had 100 ohm resistors that weren't close enough to tame all the hum - I've bought 1% 2W resistors ever since and they have never let me down.
     
  8. Lowerleftcoast

    Lowerleftcoast Tele-Afflicted

    Posts:
    1,712
    Joined:
    Dec 30, 2019
    Location:
    california
    I will disagree with @gusfinley. The frequencies on either side of the of the 6.3V pair may not be quelled with perfectly equal resistors. The secondary wire in the transformer and variations in the tubes can make the two halves of the 6.3V pair unequal. According to the Valve Wizard the "...'humdinger' pot can then be adjusted on test for minimum audible hum, which seldom occurs at the exact centre setting."

    I just want to say there usually is more to an artificial tap than just providing two equal resistors, and a humdinger is not used to provide equal resistance to each side of the heater wire pair. It is used when two 100ohm resistors cannot get the job done.

    Personally, I have not heard a need for a humdinger pot yet on a guitar amp, and I believe gusfinley has had success with his method.

    A lot of the time *close enough* is close enough to keep hum at bay.
     
    King Fan, James Knox and Paul G. like this.
  9. King Fan

    King Fan Poster Extraordinaire

    Posts:
    5,457
    Joined:
    Jan 1, 2013
    Location:
    Salt Lake City
    FWIW Merlin has a nice discussion of these heater-hum-taming methods.
     
    Tele Slacker likes this.
  10. James Knox

    James Knox Tele-Meister Ad Free Member

    Posts:
    474
    Joined:
    Aug 13, 2003
    Location:
    Phoenix
    Thanks for that link KF! I’ve seen the pics of “the right/wrong way to run heater wire” nut never read the whole article. I have it bookmarked now!
     
  11. James Knox

    James Knox Tele-Meister Ad Free Member

    Posts:
    474
    Joined:
    Aug 13, 2003
    Location:
    Phoenix
    Ok, I hung them on the power tube!
     
  12. Tele Slacker

    Tele Slacker Tele-Meister Silver Supporter

    Posts:
    152
    Joined:
    Jun 28, 2009
    Location:
    South Carolina
    2nd that! Thank you for the Merlin Link.
     
    James Knox and King Fan like this.
IMPORTANT: Treat everyone here with respect, no matter how difficult!
No sex, drug, political, religion or hate discussion permitted here.