Electronic Surplus still has some Victoreen parts:
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Electronic Surplus was only a few miles from the Victoreen plant and would often have surplus parts.
We purchased some of those vacuum glass tube resistors from E.S. they may still have a few.
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Electronic Surplus was only a few miles from the Victoreen plant and would often have surplus parts.
We purchased some of those vacuum glass tube resistors from E.S. they may still have a few.
Lets see. It would take 39 KV to make 1.5 W in a 1G ohm resistor.
I just can't imagine what a 1G ohm resistor would be used for.Bobby Dipole
For audio, not much. But it is a common size for range divider networks in high impedance electrometers. Also for sensitive current amplifiers as well as range resistors in megohmmeters. Older Geiger counters use very high megohm resistors on their inputs. Generally on the order of 50 gigohms and up. These were the glass encapsulated types that Victoreen made.
As said before: just buy one.
Re: what would they be used for? I worked on a product that used a piezo-crystal sensor (inherently AC and capacitive), but they wanted near DC response; so we used the sensor in the feedback loop and the 1 Gigohm resistor as the input resistor IIRC.
Problems: Our resistor was surface mount, and I used lots of alcohol and maybe freon cleaner to make sure it was clean of flux (mostly underneath). Then we encapsulated the whole circuit to avoid humidity effects. We shielded it to avoid responses to static electricity. Something, probably the op amp, was also photosensitive, but the shielding and encapsulation eliminated that issue. All said, it wasn't that bad, if you need it - do it. If you don't need it - then avoid it.
Re: what would they be used for? I worked on a product that used a piezo-crystal sensor (inherently AC and capacitive), but they wanted near DC response; so we used the sensor in the feedback loop and the 1 Gigohm resistor as the input resistor IIRC.
Problems: Our resistor was surface mount, and I used lots of alcohol and maybe freon cleaner to make sure it was clean of flux (mostly underneath). Then we encapsulated the whole circuit to avoid humidity effects. We shielded it to avoid responses to static electricity. Something, probably the op amp, was also photosensitive, but the shielding and encapsulation eliminated that issue. All said, it wasn't that bad, if you need it - do it. If you don't need it - then avoid it.
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All resistors can have a maximum voltage rating and maximum power rating which are separate and cannotbe extrapolated!
The max power is a function of the package dissipation and could not be reached before the maximum voltage rating kicks in (arcing, breakdown etc, even for an infinite resistor.)
Well, that was kind of my point. By specifying the power requirement the OP is implying that the voltage present across the resistor will be very high. Otherwise the power rating is quite moot.
Maybe he's going to measure the voltage from a Van Der Graaf generator, who knows?
I don't have a conclusive answer, I was the mechanical engineer and am not very familiar with the circuit function. I did do the fabrication and testing though.
While developing the prototype, we saw the output drifting seeming at random. In the lab, under normal florescent lights, we found the op amp output changed as we moved a paper over the circuit and casting a shadow on it. Moving the paper away returned to the original value.
I am only guessing that the input bias current and/or input bias voltage were being affect by the light. Given the really high impedance of the circuit resulted in significant voltage swings (around 0.5 volts as I recall). The negative input had only the 1 gigaohm resistor and one side of the piezo sensor connected to it. So this kind of output could be caused by just a nanoamp shift on the input.
Once we realized that that the circuit needed to be shielded from light, electrically shielded and hermetically sealed, we got the performance we wanted. The electrical shield also provided excellent light shielding, so we didn't analyze the problem further.
Hi all,
& thanks for all your replies ... Surprised at the amount of thoughts and exchange the question has set about
And then I'll have to apologize to you all - I have, for various reasons, decided to let my project go so I won't be using the 1 Gohm resistor ....
And to those of you who have asked what the 1 Gohm was for, I can say that it was for a capacitor microphone design. From the + volt supply to the capsule - to allow for a very low cut-off frequency.
Again thanks for replying!
Jesper
& thanks for all your replies ... Surprised at the amount of thoughts and exchange the question has set about
And then I'll have to apologize to you all - I have, for various reasons, decided to let my project go so I won't be using the 1 Gohm resistor ....
And to those of you who have asked what the 1 Gohm was for, I can say that it was for a capacitor microphone design. From the + volt supply to the capsule - to allow for a very low cut-off frequency.
Again thanks for replying!
Jesper
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