Gewikkeld draad trimmers

Dear friends

I am uploading a photo of the general types of wire trimmers used in the Philips tube radios in the oscillator and antenna circuits. In the 1st type there is no wire on the ceramic tube and only a joint (a) is there at one end which forms one terminal and the other is the wire which is inside the tube. In the 2nd type one end of the wire is soldered to the joint on the tube. In the 3rd type the wire is extended nearly up to the ceramic tube and the joint is slightly earlier to the end. In the fourth type one end of the wire is not connected to the joint(a). And in the last type the joint is not there and the end of the wire itself forms one of the terminal.
I am restoring the sett BX696A which is similar to BX695A and the forth type of trimmer has been used in position C18. Now my question is that is it not necessary to join the the end of wire to the joint (a) which forms the second terminal?. In the present case both the end of the wire is not connected. Only the joint (a) forms the 2nd terminal.

Best Regards
P.Rajan

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As far as I remember that type of trimmers always is wax-dipped
Which serves as protection against corrosion. The location where
the connection "A" on your drawings has been soldered is a short,
thin silver plating on the porcelain. The wire spiral starts where
the silver ends
Well, this wax does not give eternal protection, in some cases it
even forms acids - - end of the silver plating....
The capacity of your trimmers might well be pretty far less than
10 pF ; did you measure that?
Nico

--
een kinderhand
is ook weer gauw leeg

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The wire should always be connected tot the joint (a). An unused trimmer has a ceramic tube full of wire. The capacity is than always higher then the value that is neccesary in the circuit. During trimming the wire is unwinded from the tube until the right value is reached in the circuit. Then the loose wire is cut, en the circuit is trimmed properly.

Piet

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