Input Choke

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C Moore
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Input Choke

Post by C Moore »

Is there any tolerance when using a choke in the power supply?
Just for discussion purposes, if you were to put a smaller choke in a Fender Super Reverb AB763; would there be less filtering and less of a voltage drop? I do not know what they are rated at, but say you went from 10H to a 5H. Would the filtering and impedance be less in the smaller choke?
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David Root
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Re: Input Choke

Post by David Root »

Not necessarily either I think.

Voltage drop depends on the DC resistance of the choke, not the inductance.

Inductance doesn't filter the way a filter cap does, it just resists voltage change and that has a smoothing effect which is similar to that part of what a cap does.
tubeswell
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Re: Input Choke

Post by tubeswell »

But there is a relationship between choke inductance and filter cap capacitance when figuring out ripple rejection. See on this page about 1/2 way down - http://www.freewebs.com/valvewizard1/smoothing.html
C Moore
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Re: Input Choke

Post by C Moore »

tubeswell wrote:But there is a relationship between choke inductance and filter cap capacitance when figuring out ripple rejection. See on this page about 1/2 way down - http://www.freewebs.com/valvewizard1/smoothing.html
Merlin....Again....
Pretty interesting, thanks for the link.
So what does that tell us about a choke in this position?
If it falls into Merlin's math formula, can you feel just as happy using a 5 Henrie choke ans you would a 10?
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David Root
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Re: Input Choke

Post by David Root »

Sure, it depends on what you're doing downstream. How many stages, what kind of topology, hi-gain, lo-gain, spongy bass, tight bass, where the tonestack is (I guess that's topology).

I guess what I'm saying is there are no cast in bronze answers. Try 5H, try 10H, which do you like best?
C Moore
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Re: Input Choke

Post by C Moore »

David Root wrote:Sure, it depends on what you're doing downstream. How many stages, what kind of topology, hi-gain, lo-gain, spongy bass, tight bass, where the tonestack is (I guess that's topology).

I guess what I'm saying is there are no cast in bronze answers. Try 5H, try 10H, which do you like best?
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I have no formal education, and I REALLY APPRECIATE all the help I get from you guys. AND, I respect and admire some of the degrees you guys have. I also tip my hat to all you guys that have picked up a lot of knowledge without going to a college/university.
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TheGimp
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Re: Input Choke

Post by TheGimp »

Hammond shows the replacement inductor for the 125C1A as a 4H 90mA 108 ohm inductor.

In that particular schematic a smaller henry rated choke would result in more ripple on the input stage supply. However if you went with a 5H inductor you would actually have more inductance so you would get less ripple.

Greater DC resistance would result in more voltage drop, although you have 5700 ohms of dc resistance already so unless you are talking about a major change in the rating of the inductor you won't see much effect.

The impedance of a 4H choke at 120Hz is 3016, so the impedance is nearly 30 times the DC resistance.
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