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Offline zarkinos
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« Reply #10 on: March 05, 2012, 04:10:15 am »
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 GD348 Heathkit / he works at 110KHz

regard

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« Reply #11 on: March 09, 2012, 01:56:02 pm »
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 Shocked 110Khz for a VLF detector?

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So many questions so little time
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« Reply #12 on: March 09, 2012, 03:10:34 pm »
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Yes it is correct if you see the coil and condensers!
I worked on this machine for several months and I did this strange machine> 

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video 2012 02 24 18 16 54
   regards zarkinos

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« Reply #13 on: March 09, 2012, 05:35:30 pm »
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We have Radar detectors here too! Wink

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« Reply #14 on: March 09, 2012, 10:07:49 pm »
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New to Board, If possible could some one post a larger copy of the schematic for this unit Grin

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« Reply #15 on: June 08, 2014, 02:47:33 pm »
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 :oTo bad i am to new member of this forum i cant download it!! Cry Cry

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« Reply #16 on: October 31, 2014, 04:27:42 pm »
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I am thinking of building the gd348 just for the fun of it. can anyone tell me does this search coil have a bucking coil or is it just two concentric coils and whats the diameter on the tx coil. I see 10 to 11cm for the rx but nothing for the tx.

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« Reply #17 on: November 04, 2014, 11:13:49 am »
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Yes you will have to have a bucking coil on this setup in fact all concentric coils require a bucking coil. TX coil is normally twice RX or 22cm   

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« Reply #18 on: November 05, 2014, 07:45:36 pm »
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i just hate concentric coils. too much trouble to wind without much benefit in terms of performance against the double d arrangement. i'm no expert but i remember reading somewhere that the bucking coil actually forms part of a hartley oscillator(the feedback loop portion). the heathkit TX oscillatory don't look much like a hartley. in fact its a relaxation oscillator. oh well, maybe somethings are better left alone. the next obvious question is which one of the turns indicated in the Tx coil would be the bucking coil? Is it the 3 or the 5 or maybe the 12 turn segment. Similar designs include the vintage golmaster 66, the bounty hunter TR 600/700 and the micronta deluxe metal detector. All solid state devices featuring the multicoil design. Since the Transmitter frequency are around 100khz and also modulated at somewhere around 500hz(relaxation oscillator design using multitap coil) then perhaps one could use a double d design using a unijunction transistor in the Tx oscillator to modulate the Tx signal. Then all that would remain would be to calculate the number of turn etc. to obtain the desired inductance to acheive the required resonant frequency. other small modifications would be required but by then you would have built an entirely new detector! Maybe not worth the trouble. i love these vintage detectors. they are so cool.

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« Reply #19 on: November 07, 2014, 06:02:51 am »
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The bucking coil is actually a part of the TX coil but in reverse and on top of the RX coil to shield it from the TX signal.

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