Power Choke Dissection

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CJ

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OK, equal time for the lowry power choke.
Get out the Ny-Quil to enjoy this dissection.

This one is a Thordarson 20C55, which of course, is the only one not in my catalog. All the more reason to hack it! I had all the details in one short hour.

The victim:

ck_1.jpg


This guy measures out at 4.78 Henries on the Sencore bridge, 5.1 Henries on the B-K, and 2.7 Henries on the Gen Rad. The lower reading is because the Gen Rad osillator is running at 1000 hertz, where-as the other machines probably estimate inductance at 60 hz.
DCR was about 72 ohms.

This choke is made for high voltage tube type power supplies.
It weighs 3 lbs.

Bottom view, two leads, black goo on the lams, two end bells:

http://vacuumbrain.com/The_Lab/TA/Thordarson/Choke/ck_2.jpg

Bell covers off. Those are fake keeper lams on the outside, made out of paper. They "block" the coil for tightness:

ck_3.jpg


The I bars are all stacked together. Not a lapped lam construction like audio transformers. This is in order to handle DC . There was no paper gap between the E and I lams:

http://vacuumbrain.com/The_Lab/TA/Thordarson/Choke/ck_5.jpg

The coil was just back and forth windings with 0.0025 kp (kraft paper) in between the layers:

http://vacuumbrain.com/The_Lab/TA/Thordarson/Choke/ck_7.jpg

Using the plastic persuader to seperate the core from the coil. Along with the always present heat gun:

http://vacuumbrain.com/The_Lab/TA/Thordarson/Choke/ck_8.jpg

Coil off the core:

http://vacuumbrain.com/The_Lab/TA/Thordarson/Choke/ck_9.jpg

Leads are secured and insulated with some tape that runs thru the coil:

http://vacuumbrain.com/The_Lab/TA/Thordarson/Choke/ck_10.jpg

Varnish impregnated coil:

http://vacuumbrain.com/The_Lab/TA/Thordarson/Choke/ck_11.jpg

Interlayer paper:

http://vacuumbrain.com/The_Lab/TA/Thordarson/Choke/ck_paper.jpg

Lam type. 0.018 barn roof steel, (non grain oriented silicon), type MH 112,
1.115 inch stack, 62 lams:

http://vacuumbrain.com/The_Lab/TA/Thordarson/Choke/ck_lam.jpg

Pressboard former:

ck_former.jpg


That's about it. Oh yeah, turns: 24 layers, 85 turns per layer, back and forth winding of 0.013 in. enameled copper, 28 gauge, 65 ohms per 1000 ft, 72.7 turns per inch, 2040 turns total.
Wire length: about 1140 ft.

OK, easy construction, but still not really something you would DIY, unless you were trapped on a small desert island and needed a choke. Much easier/cheaper to buy one, as they make them by the thousands.

cj
 
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