Paolo Cravero as2594

#185

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

-- 
QRPp-I #707  + www.paolocravero.tk +  I QRP #476
  Beacon @ 28.3219 MHz + QRPp + QRSS3 + JN35TC

Rahul Srivastava

#186

Hi!

?

I?fashion them out of?glass epoxy PCB material. Much scrapped double sided? PC boards are available..?cut a strip from?area without copper traces ie normally the edges .

File and shape the strip to the desired size of screwdriver you want.

Good durable?non-conductive tool it is.

?

73

?

Rahul VU3WJM

?

?

Paolo Cravero as2594 wrote:

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 -- QRPp-I #707? + www.paolocravero.tk +? I QRP #476 ?? Beacon @ 28.3219 MHz + QRPp + QRSS3 + JN35TC

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Mike W

#188

On 13 Jul 04, at 9:52, Paolo Cravero as2594 wrote:

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.
Whats wrong with the old plastic knitting needle ?. When playing 
with HV circuits they are a lot longer and therefore safer.

Another useful tool is a tuning wand, brass ferrule on one end of a 
knitting needle and a ferrite ferrule on 'tother. When placed into the 
flux field of a coil the ferrite end raises the inductance and the 
brass end reduces it. Enabling a relativly easy way to determine if 
the coil is too big or too small. Sadly, AFIK, it does'nt work with 
toroids though.
atb Mike W
--

Paolo Cravero as2594

#189

Mike W wrote:

following Arv Evans's useful tips I would like to share with you how I
built a non-conductive screwdriver to regulate capacitor trimmers.Whats wrong with the old plastic knitting needle ?. When playing with HV circuits they are a lot longer and therefore safer.WOW! Got to ask my mother if she has some spare plastic ones!

For those non-native English speakers that might wonder what a "knitting needle" is, see the description here  or just the picture here 

Now I wonder if knitting needles are more widespread than toothbrushes! :-)

Paolo

PS: if someone ever makes a component bag for BITX20 s/he should consider adding a knitting needle or a toothbrush to the complete set of tap washers! :-)

-- 
QRPp-I #707  + www.paolocravero.tk +  I QRP #476
  Beacon @ 28.3219 MHz + QRPp + QRSS3 + JN35TC

Hubert Smits

#190

Hi Paolo,

I cut/filed a piece of PCB to the right size and
sanded of the copper. The slight advantage over a
toothbrush is that the material is less soft, so it
can handle screws that are tight or stuck.

72 de Hubert

--- Paolo Cravero as2594 <pcravero@...> wrote:

Show quoted text

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.

Arv Evans

#194

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Paolo

In the US, plastic knitting needles are available for an attractive price.? These range from 1/8 inch to 1/2 inch diameter.? The smaller ones are easily ground to a screwdriver point using sandpaper taped to a flat surface.
If one is careful you can even shape them to hex or octagon shapes for adjusting slug tuned coils.

TIP:
For trial testing of coils to see if they need increased or decreased inductance you can build a simple tool to temporarily shift the inductance up or down.? Use a plastic drinking straw and insert a small brass rod (about 1/4 inch long) into one end.? Insert a small rod of ferrite material (a chunk of broken ferrite ring works fine) in the other end.? Now you can temporarily insert either end into your coil-under-test and observe the results.? The brass will cause an increase in frequency (decreased inductance) and the ferrite will cause a decrease in frequency (increased inductance).
No, I have not tried this with the "Tap Washer Toroids" used in the BITX20, but I will later today because I am curious to see what the results might be.

Arv
_._
On Tue, 2004-07-13 at 01:52, Paolo Cravero as2594 wrote:

Show quoted text

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 -- QRPp-I #707? + www.paolocravero.tk +? I QRP #476 ?? Beacon @ 28.3219 MHz + QRPp + QRSS3 + JN35TC

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Inexpensive plastic screwdriver

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