I didn't need another project -

[Ferric Toes]

-but spotted this on ebay at the end of August. . Price was $250 which I thought was reasonable for the unit which appeared in good condition, but was untested. Shaft, charger, and belt are all there too. It arrived today and I was pleasantly surprised that the unit was even better than anticipated. It doesn't appear to have had much use at all. I charged the battery and with coil connected it did not work i.e. no TX pulses. However that is not a problem as I was involved in the development of this detector in 1982 and the electronics is very straightforward. In fact, I plan to upgrade it with all the latest circuitry and a Li-ion battery instead of the heavy Ni-cad cells. I will use a different search coil as in those days coils were unshielded. Should help to while away the coming autumn evenings and the Covid restrictions. It was interesting that this detector came from Florida and was the result of a find in a storage container sale.

Eric.

[ivconic]

"... in 1982..."
38 years old and yet in such good shape, that's rare.
I assume there is no mcu inside, only analog parts?

[Qiaozhi]

Is this the schematic for Garrett XL500 Sea Hunter.?
I've also attached some marketing blurb.

[kt315]

thank you Qi. i did not have this marketing blurb. good COVID-19 project.
yes, this detector have full diggest of pics and schematic. i bought this Garrett, first i did i rewinded
a transformer in charger on our standart, 220V AC. then i did notice Ni-Cad cells are dead all.

[Ferric Toes]

I have an original production schematic from Garrett, so can check those posted against mine; in due course. Production proper started in 1983; earlier ones were largely for test purposes. I'm not sure when it finished, but would likely coincide with the release of the SeaHunter 2.

I haven't examined the circuit board yet in the one I have, but in some of the posted schematics above, there are some differences in components, plus, maybe some errors e.g. never heard of a 704. I haven't found a serial number yet, but maybe there is one inside which would give a clue as to it's age.

Charles Garrett made an interesting observation in one of his letters. "I have found personally that United States coins can be found in salt saturated sands much more deeply than the same coins through air. Perhaps the salt water makes the target surface more conductive".

Eric.

[kt315]

perhaps Charles Garrett had in mind 'Gallo Effect'. yes, perhaps the gallo of coin is a bit much more deeply in salt water.

[ionut_mtb]

Got one for 100€ without battery. It is on the way.

[Vadim18]

Nice and fun project. Will be interesting to see performance before and after upgrades.

[kt315]

I have an original production schematic from Garrett
---
Eric, if be honestly, did you project this schematic? pleasure.

[surfdetector]

Got one for 100€ without battery. It is on the way.

That seems like a good price. I will be interested to hear how well it works.
Cheers

[Ferric Toes]

I found that the XL-500 works after all without any repairs needed. I thought there were no TX pulses, but with the board out of the box all is OK. TX transistor is a Mosfet RFP8N18L. RX line up is OPA37; Jfet gates 2N5566, integrator CA3140, d.c. amp. 741. There is also a LM358 and a CA3290. Not sure what the latter does at the moment. All voltages and pulses appear OK, although not accurately measured at the moment.

Serial no. leads me to believe it is 1973 production, but anyone familiar with Garrett numbering could perhaps confirm this.



Eric.

[Xtrem]

I believe it is made about 1987

[kt315]

I believe it is made about 1987

[ATTACH]53232[/ATTACH]

perhaps Melbeta. do not remember who made a list.

[Ferric Toes]

I believe it is made about 1987

[ATTACH]53232[/ATTACH]

You are not far off. I found a QC date stamp on the chassis - 15th March 1989. That explains the upgrade to a Mosfet and the OPA37.

Eric.

[Vadim18]

Quite impressive opamp for 1989, with great noise and bw performance. I guess in the XL500 detector opa37 should have feedback resistance less than 1000kOhm.