This is not for the unexperienced. And may be dangerous to people which have not worked with high voltage. Try this trick. Place a 1/4 watt 10 meg carbon resistor in series with another resistor of higher wattage of around 100k in series with a high voltage power supply. Put an ammeter in series, (this will be your current to figure the value of resistance you will ultimately have) but make sure it is on the ground side of the circuit where the 100k resistor is, and the high voltage power supply can be grounded on that side. When the current lowers to the value to which calculates to the ohmmage you need, remove the high voltage from the circuit. (The current you need to make your resistor R=E/I). But you need to know the voltage supplied by the high voltage supply. It may be beneficial to arc the connection by touching the h.v. source and drawing an arc to limit the current, then get closer as the current decreases. The 100k resistor is only a precaution. To be extra safe put some plexiglas over the components in case of minute flying debree.
It's easy to calculate the resistance of resistors in series just add them together.
If anyone has enough experiance with electricity they'll kno ohms law so they'll be able to calculate the resistor values without doing any experimenting.
It's easy to calculate the resistance of resistors in series just add them together.
If anyone has enough experiance with electricity they'll kno ohms law so they'll be able to calculate the resistor values without doing any experimenting.
The Idea is the 10 meg resisor is being altered to the value you desire. Presently unknown. The changed value of the 10 meg can be up to and greater than 1 gigohm.
Nigel,
A play on words!
Long long ago in a galaxy far far away, we used to use a triangular file [engineering type]
to cut a 'V' notch in carbon resistors in order to trim to a higher value!..
Be careful what you say, in another Universe it could be true.
Nigel,
A play on words!
Long long ago in a galaxy far far away, we used to use a triangular file [engineering type]
to cut a 'V' notch in carbon resistors in order to trim to a higher value!..
Be careful what you say, in another Universe it could be true.
The Idea is the 10 meg resisor is being altered to the value you desire. Presently unknown. The changed value of the 10 meg can be up to and greater than 1 gigohm.
Yeah, this is a terrible idea. Not only presently unknown, it will remain unknown in the future too. All the way up to the point when it fails altogether. Sometimes debugging circuits is hard enough let alone introducing something has hokie-pokie as this.
I take back what I said as I'm obviously too young to have heard of the method. Nevertheless it sounds a stupid idea, I suppose you could reduce a self healing capacitor's value by overvoltaging it which is also pretty silly.
I am using it in an op amp for a very high input impedance non inverting input connected to a ground reference . It remains stable because it is subjected to negligible current. If you look at the resistor carefully you wouldn't know that it changed in value. There is no discoloration.
Why say more? Some of you guys speak before reading.
I am using it in an op amp for a very high input impedance non inverting input connected to a ground reference . It remains stable because it is subjected to negligible current. If you look at the resistor carefully you wouldn't know that it changed in value. There is no discoloration.
Why say more? Some of you guys speak before reading.
What do you mean it stays stable because there is negligble ground current? That would just make it ultra sensitive to noise especially since anything could induce a current at least comparable to the current flowing (plus the noise from such a large resistor itself).
I am using it in an op amp for a very high input impedance non inverting input connected to a ground reference . It remains stable because it is subjected to negligible current. If you look at the resistor carefully you wouldn't know that it changed in value. There is no discoloration.
Why say more? Some of you guys speak before reading.
You cannot discern what happens to that resistor material at the molecular level by looking at it (for discoloration)!!
Just because it carries low current doesnt mean didly-do-squat. It remains stressed by the voltage across it. And since its material properties have changed due to your torture test, it may eventually go out of spec (failed)
If you say you do not care if it changes value or eventually fails, why use it all all then? why not just put a finger nail clipping there to make a 10G-Ohm..
Really, what you have done to the resistor is BAD. Don't do it. Go buy a suitable value. The only trick is the deception that your part is still usable/good.
I used to alter some of the older carbon types by filing them, but not
making a vee-notch, it was by making a flat along one side up to the
connection at each end.
Not much of a flat, this was only to make minor adjustment to the
value.
I suppose a vee-notch would make a very local resistance change, it
might also make it more likely to break at that place.
Just leave a gap in the tracks on the PCB and shade between them with a pencil.
If you want an amplifier with a high input impedance use a TL081 as a unity gain buffer, it will be more stable than a bodged amplifier made with destroyed resistors.
If you want a gig resistor, Digi-Key has them for $4.00 and change. Not much danger there, plus they are 1% tolerance. You can get up to 5 gigs.
The file technique was to start with a 2 watt 1 ohm resistor and cut a notch until the desired higher value was reached. Then you put corona dope on the cut to keep moisture out.
If you want a gig resistor, Digi-Key has them for $4.00 and change. Not much danger there, plus they are 1% tolerance. You can get up to 5 gigs.
The file technique was to start with a 2 watt 1 ohm resistor and cut a notch until the desired higher value was reached. Then you put corona dope on the cut to keep moisture out.