| | Quote: | | | Posted by {author} | | | |
| germanium pnp transistors. are they not obsolete? | |
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Thanks for taking the time for posting this to the forum, fellow metal detector builder!
Yes, the germanium pnp transistors are in fact obsolete. On top of that, they are Russian transistors, so they would be hard to find (unless you happen to be in Russia!). You can occasionally find old transistors for sale on ebay.
The title in Russian from the youtube detector I watched was called "40 year old detector" but it really looks like it is a 50 year old design from the sixties.
This, however, would not be my first choice if I was building a BFO detector. Mostly because it would take work to engineer the circuit using modern easily available components, and the coil would need redesigning. If you peruse the 'downloads' section, you will find a schematic for an equivalent "BFO" detector which would most likely perform equally well if not better, that was published in EDN magazine in 1997. You could probably build a similar coil for it that was shown in the youtube video for the Russian detector. The coil diameter actually is what relates to what depth that it has, and it is not necessarily "unbelievable" - as sometimes is the case there is more "hype" than reality when selling a particular design! But it is part of the metal detecting business. I think how successful your detector is depends on how much you are willing to dig!
I enjoy these old circuits not so much for the intent of building them, but more from a historical perspective to see how they were designed and how the transistors would be biased. The most practical use for a circuit like this today actually would be in a "pinpointer" design.
It is rewarding to understand how modern detectors work, but it requires a lot of effort, as they can be quite complicated. There is a book published by Carl Moreland called "Inside the Metal Detector".
I am not active in the forums too much these days, as I have other obligations and persuits. But I wanted to chime in here as it is not too often that someone posts a schematic for something!
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« Last Edit: October 31, 2014, 04:27:46 am by technos »
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