Choke Question

[J Rindt]

http://el34world.com/Forum/index.php?topic=17495.msg175610#msg175610

In reference to another post made.....
I have worked on many amps with a Pi Filter...but I never thought to put a meter across the Choke.
I checked Resistance of the choke in the AC100 (nothing else was attached to the choke) ...and the meter says 300 Ohms.
Is it "common" for a choke to read that high.?
For some reason, I though the DC Resistance of a choke would be pretty low.
Maybe it is 300 Ohms, so  to facilitate the 20 Volt drop, and Screen Regulation that sluckey was discussing.?
Thank You

[sluckey]

300Ω is a common resistance value for a typical choke used in a guitar amp. You can easily see a resistance range from 50Ω on up to above 600Ω, even higher. The choke is just a long piece of wire coiled around some iron. The wire has resistance. Longer wires have more resistance.

Most chokes have 3 important electrical characteristics associated with them. Inductance, DC current rating, and DCR (resistance). Look at the Hammond MFG. website for some typical values for their chokes.

[J Rindt]

OK...Thanks.
For some reason I had it in my mind that a choke would have very low DCR...just an assumption on my part.
Is the  reason for "High" DCR to drop the B+ for the screen supply, or is there/are there  anothger reason(s).
Thank You

[HotBluePlates]

I checked Resistance of the choke in the AC100 (nothing else was attached to the choke) ...and the meter says 300 Ohms.
Is it "common" for a choke to read that high.?
For some reason, I though the DC Resistance of a choke would be pretty low.

It's very low, compared to its impedance to power supply ripple.

X_L = 2 * π * f * L = 2 * 3.14 * 120Hz * 15H = 11kΩ.

To get the same filtering effectiveness while using a resistor, you'd need an 11kΩ resistor which will drop almost 38 times as much voltage.