Opinions on replacing Choke

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by AshlandBump, Jun 15, 2006.

  1. AshlandBump

    AshlandBump Silver Supporting Member

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    I've moved this message over from the general amp forum, it seems better suited here:

    I've heard different opinions about whether a choke makes any difference in the way an amp sounds. Does anyone who's more informed than I am know whether there's any truth either way? If different choke can make a difference in tone, how much so? Thanks.
     
  2. hasserl

    hasserl Member

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    This is true, but since most guitar amps that use a choke place the choke after the plates of the power tubes, to supply the screens and preamp nodes, is this additional stability really an issue? Neither the screens or preamp tubes use much current, not enough to cause a sag in the power supply, which is what the main advantage of a choke would be. Placing the choke first in the power supply will give stability to the entire amp, and would have a more profound effect on the sound. But this is rarely done, and I can't thiink of a major common amp that does this (I've got a homebrew amp that uses a choke input).

    I'm not implying that a choke does not effect the overall sound of an amp, but if it does, why? I'd say it has less to do with any voltage drop at full output, and more to do with less ac ripple in the power supply to the screens and preamp.

    No?
     
  3. John Phillips

    John Phillips Member

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    I totally agree with hasserl. IMO, as long as the choke is roughly in the right ballpark for inductance (which does affect the amount of ripple on the supply), it makes no significant difference to the tone - any more than the type of the B+ chain resistors do if they're the right value.

    The current through it is almost constant (only the screen current changes, and it's quite small), so it has virtually no dynamic characteristics that you need to worry about, and its DC resistance is not much more than effectively zero either, so the voltage drop across it is very small.
     
  4. AshlandBump

    AshlandBump Silver Supporting Member

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    Thanks for the responses. The question isn't so much about the benefits of choke vs. non-choke design or the merits of the placement of a choke. I'm wondering if replacing the existing choke with what is purportedly a more "vintage accurate" choke would make much, if any, difference in the tone of the amp. Specifically, we're talking about swaping a Hayboer choke for a Mercury Magnetics choke -- both companies produce quality transformers.

    I admit that I have no technical knowledge whatsoever when it comes to the guts of amp, aside from being able to replace tubes. Based on that lack of knowledge, I translate what John Phillips said, above, to mean that one reasonably well made choke would not sound much different than another reasonably well made choke, but perhaps I'm wrong. So, any more insight or opinions would be appreciated.

    Thanks.
     
  5. VacuumVoodoo

    VacuumVoodoo Member

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    Your understanding of what John said is correct.
     
  6. pfrischmann

    pfrischmann Member

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    I swapped out my 70"s Marshall choke for a 20H Mercury. I could hear a difference but it wasn't huge. It just took away a bit of the high end harshness. Seemed to make the amp a little less....cloudy. worth the $20 but not an epiphany moment.
     
  7. donnyjaguar

    donnyjaguar Member

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    Sometimes I think the chokes are in there for nostalgic reasons. :) Let's face it, you can design a perfectly fine tube amplifier without one.

    But that said, what a choke betwixt the HT and Sgrid supplies does do is provide de-coupling for the Sgrids. This allows you to run the Sgrids at close to HT voltage without any current-limiting effects of a dropping resistor. It also filters our more of the hum from the power supply as the lower-signal portions of the amplifier are more sensitive to this. The filtering on the HT supply can be pretty shoddy and you won't hear it because of the hum-cancelling nature of the output transformer.

    I agree that the best regulation can be had by running the HT after the choke. Perhaps a silly statement as this isn't conjecture, but whether this is desireable for best "tone" is.

    DJ
     
  8. John Phillips

    John Phillips Member

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    I should say that I've never compared 'similar but not identical' chokes.

    But I have on a few occasions re-replaced bodged, totally wrong chokes (in one case a car ignition coil, yes really! - held to the amp by plumbers' pipe straps :eek: ) with correct ones, and not actually noticed any major change in tone, and the only real point - aside from restoring the value of the amp - was probably just the satisfaction of doing the job right.

    I would highly doubt that a Heyboer and a Mercury of the same spec would sound any different - but happy to accept they do if anyone has tried it.
     
  9. scottl

    scottl Member

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    I have a switch on two of my amps that goes from choke to power resistor. The resistor is 4 X the size or so of the choke.... There is a huge tone difference. Both tones are great. I like the sound of the screen sag from the resistor fwiw.....

    No noise is evident in either mode.....

    I know that my repsonse doesn't address the original question, but the switch idea is tres cool IMO ;)
     

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