Inside a 1943 Tobe Deutschmann FILTERETTE element.

1941 - 1945, MB, GPW Technical questions and discussions, regarding anything related to the WWII jeep.
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YLG80
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Inside a 1943 Tobe Deutschmann FILTERETTE element.

Post by YLG80 » Fri Mar 23, 2018 9:22 am

To satisfy my curiosity and kill certain myths, I've bought a Tobe Deutschmann 1123 filterette element manufactured in 1943.
I've decided to open the can to see if the capacitor would "explode like a grenade" and if I would "die with the enclosed PCB" :D :D !

According to me there was no need to use PCB dielectric (PolyChloroBiphényle) in that device because it's operated at a very low voltage, i.e max 50V.
According to me there was no risk for the element to explode like a grenade because the enclosed capacitor should be of a low value, i.e not a high value electrolytic cap.

So let's have a look.
Here is the device :
TOBE_FILTERETTE_1123-50V-A-PIC1.JPG
TOBE_FILTERETTE_1123-50V-A-PIC1.JPG (98.94 KiB) Viewed 966 times
This is a 3A 50V model.
TOBE_FILTERETTE_1123-50V-A-PIC2.JPG
TOBE_FILTERETTE_1123-50V-A-PIC2.JPG (122.1 KiB) Viewed 966 times
In the Jeep filterette, there are 10A 30V and 55A 30V elements.
The bottom side opf the element show a hole plugged with tin. This is to fill up the can by the end of the assembly.
TOBE_FILTERETTE_1123-50V-A-PIC3.JPG
TOBE_FILTERETTE_1123-50V-A-PIC3.JPG (111.63 KiB) Viewed 966 times
I've heated up the top of the can to de-solder the tin soldered cover with the two connector tabs.
This is the opened filterette.
TOBE_FILTERETTE_1123-50V-A-PIC4.JPG
TOBE_FILTERETTE_1123-50V-A-PIC4.JPG (117.71 KiB) Viewed 966 times
While heating up the can, it was smelting wax commonly used in old electronic devices to coat/encapsulate chokes or to prevent vibrations with certain components.
Looks like light yellow beeswax.
First myth killed : there is no dangerous PCB inside the can. Only wax likely made of beeswax.
You can see the frozen wax on the above picture in the can. This is used to encapsulate the LC filter.

There are two electronic components inside that element: a coil and a capacitor to make a single ended low pass filter.
TOBE_FILTERETTE_1123-50V-A-PIC5.jpg
TOBE_FILTERETTE_1123-50V-A-PIC5.jpg (81.47 KiB) Viewed 966 times
I've measured the components :
L coil : 15µH (wood core :)!)
C cap: 0.1µF

Second myth killed : The cap is a classic paper capacitor with no PCB dielectric.
Third myth killed : that filterette enclosure would likely never explode like a hand grenade because there is a weakness at the bottom with the tin plugged hole.
If there is a pressure increase because the beeswax is very hot due to a short or a leaking capacitor, the plugged hole would likely open first.
Very big modern electrolytic caps have often a safety plug to avoid the explosion.

A better filter could replace that original one in the original can.
We could use a toroid core with high µ material (high permeability) to make the L coil and put two caps instead of one. (13AWG wire for 30V 55A)
One high value electrolytic low ESR cap (for example 680-1000µF) with a low value cap of 0.1µF in parallel with the electrolytic cap.

I hope your curiosity will also be satisfied because I've not found any technical information in the literature or on Internet about these filterettes.

Anyway, if the filterette is leaking, that means that there is a short somewhere in the jeep circuit, a leaking capacitor, or a device draining a lot of current. Drainin a lot of current usually happens in radio jeeps.
The beeswax is liquefied and may start flowing outside of the can.

I would be much more cautious with high voltage filterettes like this one. They likely contain PCB and/or a bathtub cap with PCB.
High_Voltage_Filterette.jpg
High_Voltage_Filterette.jpg (41.18 KiB) Viewed 966 times
Yves
WWII Tobe advertisement "No noise please"
tobe-filterette.jpg
tobe-filterette.jpg (61.33 KiB) Viewed 966 times
Last edited by YLG80 on Sun Mar 25, 2018 6:59 am, edited 5 times in total.
Ford GPW 1943 - Louisville - DoD 12-7-43
serial 164794


Bill M
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Re: Inside a 1943 Tobe Deutschmann FILTERETTE element.

Post by Bill M » Fri Mar 23, 2018 2:27 pm

A very informative article thank you Yves. There is a strong element of professionalism in your technical posts.

cheers

Bill
Member of G503 since 1999


GPW-178721 Under restoration.

Dwight V
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Re: Inside a 1943 Tobe Deutschmann FILTERETTE element.

Post by Dwight V » Fri Mar 23, 2018 3:19 pm

Thanks for taking the time to do this!
Lots of questions about the filterette answered.

Dwight

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Re: Inside a 1943 Tobe Deutschmann FILTERETTE element.

Post by Beers » Fri Mar 23, 2018 5:55 pm

Great information Yves, thank you for doing this and posting what you found.
1943 MB 213301 DOD 2-22-43

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Re: Inside a 1943 Tobe Deutschmann FILTERETTE element.

Post by YLG80 » Sat Mar 24, 2018 9:37 am

Fileterette's are almost useless these day's, so bypassing each filter is not a problem.

It can be a problem when reenactors are using amplitude modulated radios... (WS19, WS38, N°21, BC-611, BC-728 etc ...)

Almost nobody is still listening to AM broadcasting radios these day's, so no problem with the auto radios :)!

The filterette box could easily hide anti-theft circuit breakers :wink: .

Yves
Ford GPW 1943 - Louisville - DoD 12-7-43
serial 164794


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