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For the record, I am a lover and collector of “old technology” in the form of electronics, radios, hi-fi and technical literature. I also attend steam fairs to watch and marvel at the hissing monsters of yesteryear that plowed our farmland and hauled heavy loads. A short distance from where I live is the Great Western Railway Society where they restore the steam locomotives that pulled our trains until the advent of diesel. For the same reason, I attend at least one of their open days. Why do I “waste” my time? Take the electrical side of things; my home hi-fi is a tube amplifier, 1950’s circuit, triode connected output stage, feeding two 1960’s design tapered pipe speaker enclosures. As well as CD, I still play vinyl on a 1960’s transcription turntable. The sound? As good as any modern state of the art equipment, and that is not just my opinion. The appearance? Much less clinical, more warm and friendly plus the system is easily modified for experimentation.
So why not metal detectors? The technical paper that I still refer to today on the basic theory of PI was written in 1956. At that time it was not possible to construct a practical detector and the theory was confirmed by interrupting the current into a coil with an “iron clad mains switch” and looking at the return waveform with timer/relay circuit for the pulse delay, cathode follower, and a Cossor tube scope. This paper even gives another reference to a paper written in 1896! Up until three years ago I used a Tektronix 545 tube oscilloscope to set up both industrial and hobby PI detectors. The reliability, triggering and brightness of display was second to none. It also doubled as a room heater during the winter. I still have it as standby in case my present, admittedly smaller, lighter and more portable, scope should fail.
Like the 1956 PI paper, a study of old designs which either had serious limitations or were not even practical may bear further examination in the light of today’s technology. Who can say that the BFO will not return to popularity or that the “two box” locator does not have a future. I would love to find the time to investigate a PI two box as I think it has some interesting possiblities. Study and construction of past metal detector designs is educational at the very least and, who knows, someone may stumble on a refinement or even a totally different approach which opens up the whole technology again.
By the way Carl, I will edit and revise my “old” PI articles in due course so that you can post them in a corner on your forum.
Eric.
So why not metal detectors? The technical paper that I still refer to today on the basic theory of PI was written in 1956. At that time it was not possible to construct a practical detector and the theory was confirmed by interrupting the current into a coil with an “iron clad mains switch” and looking at the return waveform with timer/relay circuit for the pulse delay, cathode follower, and a Cossor tube scope. This paper even gives another reference to a paper written in 1896! Up until three years ago I used a Tektronix 545 tube oscilloscope to set up both industrial and hobby PI detectors. The reliability, triggering and brightness of display was second to none. It also doubled as a room heater during the winter. I still have it as standby in case my present, admittedly smaller, lighter and more portable, scope should fail.
Like the 1956 PI paper, a study of old designs which either had serious limitations or were not even practical may bear further examination in the light of today’s technology. Who can say that the BFO will not return to popularity or that the “two box” locator does not have a future. I would love to find the time to investigate a PI two box as I think it has some interesting possiblities. Study and construction of past metal detector designs is educational at the very least and, who knows, someone may stumble on a refinement or even a totally different approach which opens up the whole technology again.
By the way Carl, I will edit and revise my “old” PI articles in due course so that you can post them in a corner on your forum.
Eric.
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