Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: 12AX7 on September 23, 2022, 10:07:33 am
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I have a 6V6 build that was once a el34 build i converted. It has a 20H choke. I tried it with a resistor in place of the choke but chose it somewhat randomly because i'm pretty much a noob when it comes to theory. I liked the way it feels vs choke so want to replace it permanently but not sure how to choose the optimal wattage and resistance values. The one i tested it with was a heat sinked 15w 230ohm. What data would you need to determine what resistor would be optimal? I can tell you it uses a 630v center PT and a classictone trainwreck type 6.6k OT and 390v on the JJ 6V6's.
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It will be helpful to you to have a general understanding of this:
What is Ohm’s Law? (A Simple Explanation) | Electrical4U (https://www.electrical4u.com/ohms-law-equation-formula-and-limitation-of-ohms-law/)
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Fender's 6V6 no-choke amps varied between 1K and 5K for that resistor. I'd find a Fender schematic that's reasonably close to your amp's design and use that resistor's value as a guide. The lower the value you use, the higher screen voltage you'll get, desirable. You'll also get a corresponding increase in voltage ripple, undesirable. It's a tradeoff. Be sure to use power resistors rated for at least 1W.
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but not sure how to choose the optimal wattage and resistance values.
We'd need more information to help with that. Schematic is best.
Rating for power dissipation is a safety issue. Optimal resistance is more of a design issue.
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here ya go....
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I don't know how to model your circuit to sound "best." But you did like the 230R resistor, so just go with that.
For this tube set, your maximum current draw through a resistor in place of the inductor might be around 35mA. (Plate current does not flow through this resistor as drawn). This yields a heat dissipation of 281mW. A 1W resistor is probably ok, though I personally would use a 3W (metal oxide or wire wound) in this position.
There will be other opinions.
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Been comparing and now I think it's best with a choke, tho it does feel stiffer than i;d like. Aside from that the choke has a more solid feel and i'm wondering if a small choke, maybe 3H would give me the same sound/feel but w/o the stiffness in the feel.
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… a 6V6 build that was once a el34 build i converted. It has a 20H choke. … a resistor in place of the choke … What data would you need to determine what resistor would be optimal? … it uses a 630v center PT and a classictone trainwreck type 6.6k OT and 390v on the JJ 6V6's.
The choke provides a low resistance filter for eliminating ripple hum in the PS rail. Any resistor will need to be higher DC resistance (than the choke) if you’re using the same size filter caps*, so the resistor will end up dropping more supply voltage.
*the choke works in combination with the filter caps to do it’s job, and the rating of the choke determines the effective rating needed for the filter caps (and vice versa). Same goes for the resistor, but it does a poorer job of eliminating ripple than an inductor, so either the resistor needs to be higher resistance or the caps need to be massively higher capacitance- to get to the same efficiency as a choke.
See the formulas ('formulae') for design examples on this page http://www.valvewizard.co.uk/smoothing.html (Or better still, get a copy of Merlin Blencowe's Designing Power Supplies book)
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What’s the resistance of your choke?
As your amp has a master volume, it may be helpful to clarify how are you actually using the amp.
eg totally clean, overdriving the preamp, overdriving the poweramp, or overdriving both pre and power amps.
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Try a 470Ω/3W in series with your choke.
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Try a 470Ω/3W in series with your choke.
That would act as a sag resistor?edit: yep.