Hi,
following Arv Evans's useful tips I would like to share with you how I built a non-conductive screwdriver to regulate capacitor trimmers.
A quick glance at the BITX20 schematic did not reveal any "floating" trimcap, all of them have at least one terminal to ground.
In these situations it is important to know that the trimmer screw is electrically connected to one of the trimcap terminals: solder that terminal to ground! This way you can use any screwdriver without detuning the circuit with your hand.
Use an ohm-meter between the screw and terminals to identify which one(s) are to be grounded.
(This might be obvious, but I didn't know until a few monhts ago!)
If the trimcap is floating instead, you need a plastic screwdriver. Since it might be rather expensive to buy (at least in Italy) I built one out of a toothbrush. Toothbrush should be changed often, ;-), and it is usually made of some hard plastic (+ rubber for a better grip).
So, cut off the brush and shape the stick with a knife until you come up with something that looks like a screwdriver (flat) head. I found the plastic to be quite resistant, so you need to work it in small steps as if you were creating a wood sculpture.
Apply the usual disclaimer about personal safety while handling the knife and you're on the way to have a simple and ergonomical all-plastic screwdriver.
Has anyone identified other materials that could be used for such a purpose?
72,
Paolo IK1ZYW
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