Replacing Antenna Choke (A-K Model 37)?

[Winky Dink]

I'm working over this chassis very slowly, dealing with one component at a time. The antenna choke looked nasty:



I made a futile attempt to repair it and now I'm trying to find out how to replace it. All I know about it is what I see--the chassis (ground) bracket is the iron core, and a parts list specifies 35 ohms for the coil. Schematic is here:

https://lh5.googleusercontent.com/-_...7%25252049.jpg

One other component was missing--it looked like an empty fuse bracket:



I figured out what it was supposed to be, but my local Radio Shack had run out of 2 Meg glass-tube resistors. I found several photos on-line and fabricated my own fanciful version with appropriate length and diameter for the existing bracket:



Cute, huh?

Back to the original issue, can we determine what I can use to replace the dead antenna choke?
Thanks,
Winky

[Reece]

That's a great cartridge resistor! What did you use for the body?

As to the choke, I'd carefully unwind it and take notes. Try to duplicate the wire gauge. You can look up tables that tell you how many turns per inch for each gauge: I just closewind unknown wire on a pencil and count the turns per inch. Then tables will tell you how long a piece you need to make up 35 ohms. You made a resistor. Why not a choke?

[Winky Dink]

I considered rewinding it, but stumbled over the, "I don't even know the gauge." I think I can come close by comparing it with a couple of known-gauge I already have.

The cartridge resistor is strictly from the junk box in the garage. The tube was from the staff of a little plastic flag.



The rewind-a-choke project sounds like fun. Thanks for getting me started.
- Winky

[Reece]

Love the inventiveness. You might be able to salvage the wire from the choke, unwinding it carefully, making a few soldered splices, if it isn't potted in goo. I'll bet the exact ohms isn't that critical.

[Winky Dink]

...and the goo was hardened and it wouldn't dissolve in the usual solvents.

I made this macrophoto to compare the antenna choke wire with two known wires, and it sure looks like it's 40 AWG.



From the tables, I calculated that 33.4 feet would give me the specified 35 ohms. From my estimate of the coil circumference, that would be about 285 turns. unwinding the coil yielded approximately 42 feet of wire, but I couldn't count the actual number of turns.
Next week I'll have some 40-gauge magnet wire. I have to replicate the cardboard tube from my measurements (the original tube crumbled), then wind about 40 feet....OR I could ask this young lady:



She's working in the Atwater-Kent factory in 1925. Looks like she's making condensers, but maybe she has a friend in the coil department.
- Winky

[Reece]

I'm sure she knows. Bully for you on the rewind.

Aren't your wire labels in the macro reversed? The one labeled 40 gauge looks biggest.

[wa2ise]

Originally Posted by Winky Dink

From the tables, I calculated that 33.4 feet would give me the specified 35 ohms. From my estimate of the coil circumference, that would be about 285 turns. unwinding the coil yielded approximately 42 feet of wire, but I couldn't count the actual number of turns.

Is it part of a tuned circuit? If so, be prepared to add or remove turns to get the inductance right. The number of turns would be more important than the resistance. Or discreetly hide an adjustable ferrite core inside so you can adjust it. The ferrite core would let you use fewer turns too.

[Winky Dink]

Yup, the labels on the photo were reversed, but I think I fixed that.
I think we were using the resistance just to get an estimate of length and number of turns. If I can't get the rebuilt choke to work, then I'll think about hiding a new adjustable-core coil on the underside of the chassis.
Always grateful,
Winky