Thordarson Choke type 1-8C42

[Family_Dog]

HI All,

I found a Thordarson Choke type 1-8C42 in my rummage box. My guess is it's a DC smoothing choke, probably a few Henries at about 150-200 mA. It's size is about 4"h x 3.5" x 3.5", altrhough I haven't measured it precisely.

Any ideas as to it's value?

-Eric

[PrairiePete]

Are you sure it's not a 19C42. The old Thordarson listings I have show 19C42 as the same dimensions. 200ma, 12H, 130 OHMS DCR.

[Family_Dog]

Hi Praire Pete,

There is a small plate on the side of the choke, which reads 1-8C42. Further, there is a chrome plate on top of the choke that says "Thordarson". Any other writing on this chrome plate has been completely scratched off.

The choke is coloured gray, is about 3.25" x 3.5" square, and 4" in height. Under the choke are five terminals. spaced similar to the 5 dots on a dice. Two of these terminals are marked 2 & 3, which have a resistance reading of 339 ohms, the other two terminals are marked 6 & 7 and have a resistance reading of 393 ohms. There is also a terminal in the centre which is marked "G".

When I found it, the two sides of the (apparently) two chokes/coils were wired in parallel, i.e. resultant resistance reading of about 184 ohms.

-Eric

[Geek]

You might have to determine inductance by the method in my article here.

[Family_Dog]

Hi Gregg,

Most informative article. Not having a VTVM or FETVM, I can presumably use a scope and work out the frequency from there. I imagine it *should* resonate at either 50 or 60 Hz, depending on whether it was wound for the USA or European market. I still would not know the current rating, but I reckon I would not be far off with my assumption of 150-200mA.

One thing that puzzles me is why it has two nearly similar windings (339 & 393 ohms respectively). As I mentioned, these had simply been paralelled to give a final dc resistance of about 183 ohms. The choke was part of a power supply unit (v-e-r-y "homebuilt" by an unknown constructor) using a 350-0-350V transformer coupled to a GZ34 tube rectifier.

I think I am going to use this choke in a new 5-20 amplifier I want to build. I will use it in the parallel mode as it was previously wired up, hope there are no imbalances due to the different impedances, and see what happens.

-Eric

[Geek]

I have seen some centre-tapped filter chokes in very old TV's. The centre tap was used as the power take-off for the high current stuff, like horizontal and vertical sweep sections and the rest of the TV was fed from the DC through the entire choke. This provided for 1) lower DC voltage required by those stages, 2) stage isolation and 3) extra filtering required, especially by the tuner(s).