Chokes vs resistor

[E biddy]

Why do I want to use a choke in a power supply instead of a 10 cent resistor.

[eschertron]

Voltage. Current.

edit: OK, my answer's a bit terse. But what you want probably can't be answered without considering a number of things, so let me try again:

Tone. Money. :sigh:

OK, I give up. Why do you want to use the choke? What output power, pedigree?

[dstrat]

its one of those where everything depends on everything else.

[dstrat]

Terse: yes I guess me too.
really best reason off top of head is better ripple rejection to screen supply.
also less voltage drop for a choke.
Probably a lot of other reasons too!

[jmaf]

In short: Pros: choke drops less voltage, wastes less energy to achieve better filtering.

Cons: it's more expensive, bulky.

[Chuck H]

Cons: choke drops less voltage and wastes less energy to achieve filtering.

Pros: Less voltage drop = higher voltage on the screens when more output power is the goal.

[Chuck H]

A choke has the advantage of dropping less voltage AND being able to do it at an impedance that insulates the screen grids from the plates. Sometimes, even with resistances over 1k, a resistor doesn't isolate the screens from the plates enough to prevent excess screen current as well as the IMPEDANCE of a choke on the AC load. That's just my experience and I'm willing to accept some schooling on the particulars (please, in fact). But... As mentioned it's part of a whole system. WRT guitar amps a choke isn't better than a resistor and a resistor isn't better than a choke. They are both design elements with particulars that are dictated by, and dictate other aspects of the whole circuit. I won't go into a long explanation about "sag", etc. But the resistor option has it's place. As does the choke. Often ignored is the importance of how a choke can hold a higher voltage on the tubes while maintaining a safe relative impedance to the AC load. This, I think, is really where a choke shines.

[eschertron]

Often ignored is the importance of how a choke can hold a higher voltage on the tubes while maintaining a safe relative impedance to the AC load. This, I think, is really where a choke shines.

Are there specific tubes or a specific class (AB1, AB2) or a specific output power [all 'for examples'] where you would reject a resistor outright in favor of a choke?

[J M Fahey]

Just reminding e biddy has not told *where* would he use it ("power supply" is as generic and vague as can be) , power supply voltage and current rating, what kind of load is fed from said supply and what are design goals.

[Old Tele man]

CHOKE ( LC ) produces sinusoid-ish ripple, which is FAR easier to filter.

RESISTOR ( RC ) produces triangular-ish* ripple, which is NOT so easy to filter.

* with exponential voltage decline rather than smoother sinusoidal.

[Chuck H]

In most guitar amp designs that we know and love the choke is between the plate and screen nodes. It's there to keep the screens at a higher voltage and in a steady state for more gain, lower sag and (thank you OTM) better filtering. A choke would then be a good choice when you're design allows for it's use without excess screen voltage and you want the above characteristics. A resistor would be a good choice where you want more power supply sag or, in the case of something like a class A amp where there is not much sag anyway, you just want lower screen voltages. "I" think resistors have come into fashion for many homebrew designs because:

1: They offer power supply sag in the absence of a rectifier tube.

2: This reduces overall cost because chokes, rectifier tubes and sockets are expensive.

3: Many power transformers are either salvaged or replicas of older designs and often supply high enough voltage to jeopardize the screens in typical HV rail layouts if a choke were used.

[Helmholtz]

In most guitar amp designs that we know and love the choke is between the plate and screen nodes. It's there to keep the screens at a higher voltage and in a steady state for more gain, lower sag and (thank you OTM) better filtering. A choke would then be a good choice when you're design allows for it's use without excess screen voltage and you want the above characteristics. A resistor would be a good choice where you want more power supply sag or, in the case of something like a class A amp where there is not much sag anyway, you just want lower screen voltages. "I" think resistors have come into fashion for many homebrew designs because:

1: They offer power supply sag in the absence of a rectifier tube.

2: This reduces overall cost because chokes, rectifier tubes and sockets are expensive.

3: Many power transformers are either salvaged or replicas of older designs and often supply high enough voltage to jeopardize the screens in typical HV rail layouts if a choke were used.

And because a choke is an efficient ripple current filter it allows the use of lower value filter caps. This was a major concern in the old days.

[E biddy]

Just reminding e biddy has not told *where* would he use it ("power supply" is as generic and vague as can be) , power supply voltage and current rating, what kind of load is fed from said supply and what are design goals.

Sorry, I will get back to this tonight. Mostly it is based on the power supplies of the ampeg B-12 and the Bassman. I was going t wait until I could post schematics tonight.

[frus]

What about Hiwatts then? They certainly didn't cut the costs and probably didn't want any sag (the resistor was like 500 ohm anyway)?

[Chuck H]

What about Hiwatts then? They certainly didn't cut the costs...

Who says?

...and probably didn't want any sag (the resistor was like 500 ohm anyway)?

The resistor is shown as 100R in all the schems I've seen for the classic models. Not much sag. For the high watt Hiwatts the PT had a separate winding for the screen supply and it was pi filtered. So the idea may have been to keep those monsters as tight as possible and the hundy's were the "little" amps