Beginner would like to build Sandbanks PI Metal Detector

Hello forum readers,
Coincidentally, I would like to build the Sandbanks metal detector too! It appears that the design was very good for its time and it has certainly generated a lot of interest in this forum.
I have the original magazine from Jan. 1979 but not the revisions that were published in the April and August issues.
According to the rules of thunting.com I need to make another four posts before I am allowed to download the
corrected schematics.
Does anyone have the April and August 1979 issues of Practical Wireless that could be scanned and supplied as a PDF?
I like to have access to original documentation whenever possible. Was the Toko part (T1) removed in either of these later issues?

Regards, ramchip
 

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Thank you Homefire, that was great! I see there are missing tabs before the quantity in the parts list but that's okay. Follow-ups #1 and 2 are there, which is the main thing.
Did you make the original when it was current? If not, how did you deal with the T1 problem?
I think that part might be obsolete, but I've not checked yet. I saw the document about winding your own T1 coil and may have to try that if I can't source T1. Thanks again for your generous help.

Regards, ramchip


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I purchased two of the original kits way back when.

As Cornelious stated  bypass T1 with another battery.   

This thread has everything you need to know in it.

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For the person who is not an oscilloscope to measure time for delay and sample in the integrated interesting serious CD4011 that built this period to meter the pus onsite geotech, that performs a correct reading of the above-mentioned times
   http://www.geotech1.com/forums/showthread.php?t=14451&page=2

Carlos Daniel

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Hi all

I've built a couple of working metal detectors in the past; one was a simple BFO circuit which found me loads of silver foil and ring-pulls and the other was a VLF discriminating machine - the Practical Wireless Magnum. That *sort of* worked OK, but a friend who had built one which worked VERY well told me that he'd scaled up the PCBs by about 5% to eliminate stray RF which improved the performance. I etched new boards, but never quite got around to re-building it. Still got them, so will try and find the time soon.

I first bought the Cirkit kit for the Sandbanks around 20 years ago after another friend recommended it but couldn't get beyond that stupid CMOS oscillator stage (IC3 and associated components.) For one reason or another it got put on the back burner but I've decided to resurrect it now that I've retired and have some time on my hands.

At the time I bought a new Toko coil for the oscillator but reading this thread I now discover that it's possible to eliminate this stage by means of a second battery. I think saw a reference by Cornelius to an updated circuit diagram in the previous 32 pages but couldn't open any images in the thread (maybe because it's a very old thread?) It seemed to me that the second battery went to the input of IC8, the 12V regulator - but wouldn't that be a nonsense since the 7812 would only regulate a higher voltage downwards? Would a 9V supply here even pass through the regulator? - I don't know, since when building power supply circuits I've only ever applied a higher voltage than the desired one . . .

I've just finished etching a new PCB for it; I still have most of the components and have ordered those which I'm short of - should be here by Wednesday.

Can anybody please point me to where I can find details of the modification, or explain it to me?




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