No, not blindly at all; Fraunhofer's spectral lines are all very fine experimental evidence, from billions of atoms in dilute gasses, on many properties of (apparently identical) electrons.
Single-electron experiments in vacuo have also been performed, but aren't quite so convincing.
That's not what I remember. The 617 electrometer, and 427 amplifier used jfets (and a very clever biasing scheme that basically kept Vds at a fraction of a volt). When did they change?
The MOSFETS are Q101,2 in schematic, but in the parts list, they are denoted by double-asterisk. (**) The ** is nowhere to be found.
So it's a mystery what the mosfets were. Their replacement by jfets may be a tacit admission of their instability or just part unavailability. My Keithley
610BR uses tubes, which are still available. It also features a hand crank on the side for emergency operation in case of power failure. Does yours have that?
The mosfets are part of a subassembly. They were apparently selected parts so are not individually repleaceable. I assume they matched them for offset and selected them for leakage.
Were they ever replaced by jfets? Jfets have more leakage current.
I'll have to check.
--
John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com
Precision electronic instrumentation
I was interested in the mosfets because I had experimented with ion chamber circuits that measure small currents - fA range. Ion chambers operate at biases down to 5V, so are just collecting ion trails in air.
Glenn Knoll is the world's expert on ion chambers.
techlib.com has a nice circuit, which uses a picaxe to collect values via a
2n4117, a jfet with low leakage. (now obsolete.)
But the fact that mosfets are true field effect devices makes them sound interesting to me.
However, the Geiger counter is a better design, if you can get around the vacuum requirement.
I designed the electronics for an interesting gadget. It looked like a shopping cart that you rolled around a floor looking for radioactive particles. The bottom was a roughly 1m square coarse pixel detector. The detector was a serpentine tungsten wire sandwiched between two metalized mylar sheets, filled with some exotic gas. There was a high voltage on the wire, enough to give a lot of ion chamber gain but not quite geiger mode. We could figure out the hit locations by comparing the peak amplitudes that came out the ends of the wire.
This was a test program that I wrote.
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It worked, but never saw production. The company founder was old, and his son was flakey, and the business died before the system could be marketed. But I learned some useful stuff. Even projects that fail can teach useful stuff; in fact, they usually do.
Because it's a Bad Thing to have radioactive particles on the floor in any active or former nuclear facility, and scanning with a small detector is very inefficient. He also sold and rented people inspectors, things that employees would walk through coming to and leaving from work, to check for radiation. Some of those were mobile, shipping containers, for jobs like decontamination and disassembling nuclear stuff. Decomissioning was a big part of his business.
It was a good business, but he had no workable plan for succession.
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John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com
Precision electronic instrumentation
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