Fisher Gold Bug

[ivconic]

No.
It's the first Gold Bug, complete analogue one, obsolete.

[Hinkri]

in the first post is it a sketched diagram from the original device without changes? was it with a microprocessor?

[Op04]

When using NTE cross reference must complete with the exact suffix after part no, for LS204 According to Texas Cross ref data showing RC4558 and FOMA has confirm he open a different batch of Lobo which is using 4558 replacing LS204

[dbanner]

When looking for a replacement, I often use the nte cross reference.
A drop in replacement is not assured unless you're a datasheet jumbie.
NTE offers drop in replacement, because they are cloned under license.
Now when trying to find a suitable replacement, I first check the nte cross reference number, then I simply type in the replacement candidate number. If it carries the same nte number then I Know it's a match

[rolling rock]

LS404 ~ MC33179 (quad)

LS204 ~ MC33178 (dual)

[Andre]

LM324.

[Mrbeen]

Hi
What would be good replacement for ls404cb opamp
for origin goldbug,
, as I am not good in electronics,
Some say old lm324 but I do not know.
Any idea?thanks

[Op04]

The pcb is GB2 but, the schematic is BG1! Do you have another schematic?

Somehow I wrong placed the file, my mistake, there are none for gb1. Sorry

[Andre]

The pcb is GB2 but, the schematic is BG1! Do you have another schematic?

[Andre]

Happy new year!

[Op04]

Little update. found from Russian forum, i forget where it was exactly. I think I upload here, if this not appropriate please delete it

[dbanner]

Ivca, I've got a little surprise for you. I call it the MGSL, a tribute to your TGSL. It's a gold detector based on the minelab goldseeker 15000 schematic that's been floating around for years that nobody wants to touch with a ten foot pole.
I've picked it apart and ran a number of simulations. Made a few minor modifications and I came up with MGSL.
I post new schematic and Sims in a new thread.
BTW, that IC labeled as 3 on the original schematic seems to be transistor array chips like CA3086 or such, designed to fool reverse engineering attempts, as the chip numbers were scratched off the chips. It is totally unnecessary for a non ferrous channels implementation. A conventional channel would work just fine. At least that's my opinion.

[dbanner]

I think I know why the power supply has to be the way they designed it, for some level of precision. It may have to do with the input offset voltage error of those older typical opamps used in the circuit. These errors are multiplied by the gain of the opamp and appear at the outputs, hence the offset trimmers. Any significant variance of the power supply voltages upsets the offset trim settings, thereby introducing offset voltage errors to show up at the outputs. So you want the power supply to be as stable as possible, given some battery drain. Otherwise the detector performance will decline as the offset voltage correction goes out of whack.
The use of ultra high precision opamps can alleviate this sort of external trimming rubbish.

[ivconic]

strange how little is out there about the GB seeing how popular they were

I search quite hard for some pictures of the inside or PCB. Found a few useless ones but not a single decent one of the original GB or the GP2

Quite so.

[Koala]

strange how little is out there about the GB seeing how popular they were

I search quite hard for some pictures of the inside or PCB. Found a few useless ones but not a single decent one of the original GB or the GP2