GD-348 MD

[Esteban Cabrera Grinok]

Hi,

Anyone can send me schematic of GD-348 Heathkit MD?

Thanks in advance

[André]

Re: GD-348 MD

Hello Esteban,
Check your mail, I have sent you a scan of the schematic. The GD-348 was an excellent detector: good sensitivity to tiniest targets, good iron rejection. It's drawback: high power consumption; some chatter when touching wet grass; the need of high impedance headphones.
I used Sennheiser HD 414 headphones with 2 x 2000 Ohm.
Best regards,
André

[Esteban Cabrera Grinok]

Re: GD-348 MD






Thanks, André. I know about Heathkit products since I built the previous model GD-48 (1969), and really are sensitive mainly for old items. Some secrets as good capacitors (minimun 200 V in the transmiter stage -this transmiter stage and the preamp are in the search head-) with medium gain transistor and minimum 1/2 watt resistor in hot weather. With patience in adjustment... and you have a good detector.
I use BC547A NPN transistors.
In the GD-48 the pair transistor (current mirror) of the amplifier must be of the same gain with small derivation of gain in high temperature. The coils I paste with dark barnish used in electric motors. The trimmer of the coil receiver I use fix value (1000-1800 pF). Only the trimmer between transmiter and receiver coils I use for final and fine adjustment in stable point. The 30 pF capacitor 200-300 volt mica. The adjustment between the coils have 2 points: ferrous and non-ferrous. Choice non-ferrous critical adjustment. "Sweet iron" of old weapons are detectable, but no steel wire, nails, etc. But you can discover the steel or steel-wire, nails, etc., because in his presence the audio falls. All this for the GD-48. I hope will be the same procedure with the GD-348. See the old Heathkit I built with some war relics and coins.

Million Thanks, André

[C.Pruysers]

Re: GD-348 MD

Andre . I sent you an e-mail . Please resp. Kees

[Rudolf]

Another Heathkit




Here is another Heathkit, not tested so far.
Rudolf