Fisher 1265 Revival

[Alexismex]

Hello forum ,
Many years I practice this thing Ivconic suggested with roman clay isVERY GOOD:
Wow! So when detector adjusted just about to totally reject that material i know for sure it is ready for going outdoor and also i am sure i will not catch any falses even on hardly mineralized soils.
TOTALLY EXACT here in Mexico is the same when i pass above a piece of clay without signal i am SURE i can detect in hard mineralized soil with my pulse detector
have good days all the forum
Alexis.

[simonbaker]

Intentionally i did not mentioned few models which dont have such problem. Intentionally, because it would look like advertisment to those models. I have to point out that i am pretty objective on this matter.
So in case you are interested; XP GoldMaxx was pretty immune on roman potsherd presence, over 1e coin. As well as Minelab Sovereign GT.
And again, homemade TGSL (1265) was too, but lost some depth over potsherd , still detected 1e coin very clear in Disc mode, with Disc pot set at "3". Without 1e coin TGSL was perfectly silent and stabille on piece of clay (potsherd).
XP and GT kept the same "depths" with or without clay over coin.
All the other models (8 of major league models) were disapointing totaly, in performances, on this test. Pitty!

Your assumption reffering multi frequency...hmmmm.. We have here splitted situation; XP is single freq - working on 18kHz and Sovereign GT is multi frq . On other hand; Explorer II and DFX are also multi freq and yet those "blowed".....so...!?
I guess this is mostly related to recovery speed, yet not the only problem. I did various presets to rec speed at DFX and still no satisfactory results..hmmm...
Tough question...i dont have the right answer yet.


Oh yes...Fisher 1265 was best on this test among all other Fisher's. Lost some depth but detected coin with some cracks in sound. On real terrain i would dig such 1265 signals for sure. So ...it passed the test.

Sure, multiple frequencies not magic unless specially used to solve particular problem -- but if TGSL works pretty well, why bother! From my playing with circuits, I don't think any recovery speed would help with targets on top of each other, only if separated by horizontal distance. I would bet that if commercial detector fails with combined targets it's because they are too smart for their own good -- they have fancy target ID that works for some situation, but makes detection worse for potsherds over target!

I guess it's why people say don't choose detector on any simple test -- maybe other situation another detector does better. I think your test very important for people who search around such pottery -- air tests never would never show that!

I wonder also -- does Explorer II for example have different discrimination patterns or settings that might work better in your test?

Anyway, interesting!

Regards,

-SB

[ivconic]

Sure, multiple frequencies not magic unless specially used to solve particular problem -- but if TGSL works pretty well, why bother!

Same as if you were asked; why wish to have more than one detector in collection. There is no special reason, just love and hobby.

From my playing with circuits, I don't think any recovery speed would help with targets on top of each other, only if separated by horizontal distance. I would bet that if commercial detector fails with combined targets it's because they are too smart for their own good -- they have fancy target ID that works for some situation, but makes detection worse for potsherds over target!

But than; if those are good only to detect "clean" targets...ha,ha... who need those in real world?

I guess it's why people say don't choose detector on any simple test -- maybe other situation another detector does better. I think your test very important for people who search around such pottery -- air tests never would never show that!

Yes i agree. One test does not prove a thing. Yet, this particular test is proving a lot. Proving very important thing, very important for real prospecting.

I wonder also -- does Explorer II for example have different discrimination patterns or settings that might work better in your test?

Pitty no! I tried various setups. Than its owner tried the best he could..... no results.

Anyway, interesting!

Regards,

-SB

Specific situation i explained is not the same situation all the prospectors meet usually on their terrains, so this test does not claim that Explorer is uselles. Of course not. This only shows huge percentage on missed good targets on terrains rich with ancient ceramic and simillar stuff.
So, further, aint no wonder why same terrains keep "giving" good founds year by year, and it is good to visit those periodically. It is also good to take different devices on the very same terrain periodically.
I have nice founds on terrains, where havent in the past. Same paths, same soil...but different part of the year and different detector with me.
Most beneficial so far were Musketeer, TGSL and Spectrum to me, on "my" terrains.
Just got another Garrett GTI2500. Intend to take it with me tomorrow or day after to my favorite terrain.
Funny; just tested it same test and it is detecting 1e coin loud and clear! Wow! I havent expected that from GTI! Disc was set at zero btw.

[simonbaker]

Specific situation i explained is not the same situation all the prospectors meet usually on their terrains, so this test does not claim that Explorer is uselles. Of course not. This only shows huge percentage on missed good targets on terrains rich with ancient ceramic and simillar stuff.
So, further, aint no wonder why same terrains keep "giving" good founds year by year, and it is good to visit those periodically. It is also good to take different devices on the very same terrain periodically.
I have nice founds on terrains, where havent in the past. Same paths, same soil...but different part of the year and different detector with me.
Most beneficial so far were Musketeer, TGSL and Spectrum to me, on "my" terrains.
Just got another Garrett GTI2500. Intend to take it with me tomorrow or day after to my favorite terrain.
Funny; just tested it same test and it is detecting 1e coin loud and clear! Wow! I havent expected that from GTI! Disc was set at zero btw.

I agree with those points -- it's all interesting and I never want to stop trying to improve and try new techniques.

You say GTI succeeds at test but with disc set at zero -- what about potsherd with no coin, is it rejected with disc set at zero?

Regards,

-SB

[ivconic]

Yes it was. Totally. But in All Metal mode it was "sensed" with some mums, typical for GTI (ha,ha,ha already had it several years ago, and got pretty used on its often muming arround )

[ivconic]

It is time to "pep" this topic a bit. Where is KingJL ? Long time no see here?
Yesterday i got another 1265 on service. It is in very poor condition. VPO104N3 fet blowed already. According to what owner told me; during prospecting, suddenly 1265 started to worlk erratically and some smoke appeared from the box!!! Later he noticed that one wire from Disc potentiometer was unhooked and eventually touched something there? What? I dont know...he firstly gave detector to somebody other on service and than wire was soldered back on place.
So...i removed fet and put ordinary diode, same like i suggested in the past. NOT A GOOD suggestion! Finally i realised that!
So...after scratching head for a while, i decided to look for any p-channel fet and to experiment with it. So finally i founded J303. And wired it up there. Much better behavior! Voltages now are almost right!
So... KingJL was VERY RIGHT! 1265/66 is very tricky beast! All of the sudden most of the functions started to work right! Maybe not as original but very good. But problem is not solved. No discrimination at all. Detection in air is excellent. Both pots must be set on minimum and detector is acting very good. Once Disc pot set to "4" or higher, detector still producing very nice and pleasant tone ONLY on iron items, on coloured items tone is cracky and spiting??? I inspected all what came to my mind. Not found anything suspicious. So...decided to replace 27M4 there, U302. Can not find original so i replaced it with socket and put TL084. Now, same detection but no more cracky and spiting tone on coloured items. Same tone on iron and coloured metals when Disc on "4" and above???
No discrimination?
So i am thinking to replace U303 also.
Any more suggestion?

[ivconic]

I am also very interested in this 1265 power supply stage. This looks like very interesting design. Would like somebody more conversant to come here and explain in details its functions. FET presence is crucial here. Can not be replaced easilly.
Once i put J303 (not a proper substitution at all) there, i got proper voltages on supply rails! Wow! Before that i tried other "tricks" without success - all i got were inproper voltages.
With inproper voltages nothing works good. Detections in air very low and bad. Audio very weak. Sense pot not making differences.
But when p-channel fet put on place everything seems to came on its place: detection in air excellent, sense pot is making differences now and audio is very loud and pleasant. So...everything is about proper voltages.

[ivconic]

Bingo! Problem solved! It was all about U303!
How the heck they managed to burn it!!??? I never succeed to burn 4016 neither 4066 in all my "career" so far! So... replaced it and 1265 is working excellent....perfect! Further...this also means that my wild fet replacement do the job just fine!
Real revival, indeed.
But...i am not satisfied just with problem fixing. This device is solved but my interests are still here, about this very nice power supply.
Let's see some theories here, fellas!
Where is KingJL when i need him!?

[Ultimate_Haze]

Bravo.
Hard task.
Quick solution.
I am interested where is minelab relic hawk in this potsherd competition.I am shore that SD2000 wont have a problems at all.
Rely interesting thread.

[KingJL]

Bingo! Problem solved! It was all about U303!
How the heck they managed to burn it!!??? I never succeed to burn 4016 neither 4066 in all my "career" so far! So... replaced it and 1265 is working excellent....perfect! Further...this also means that my wild fet replacement do the job just fine!
Real revival, indeed.
But...i am not satisfied just with problem fixing. This device is solved but my interests are still here, about this very nice power supply.
Let's see some theories here, fellas!
Where is KingJL when i need him!?

ivconic,
I am still here my friend! I am not on every day like in the past, but I get alerts when threads that I have subscribed to get a hit, and I monitor some posters that I respect. My interests in the subject is still high. Just thinking more and expressing less!

The TL074 is a very poor replacement for the 27M4, but you have to use what you have available. It has ~9-10 times the current drain, higher offset voltage, and less open-end gain than the 27M4. The higher current grain will/can be an issue with the 1265. The comparator that is used to maintain the analog gnd potential can only handle ~15ma total. A single TL074 draws 10ma quiescent current (a single 27M4 draws 0.9ma). While the TL074 does have higher GBW, it is used as an active filter (HF cut-off 15-20Hz) in the 1265, so the added BW is of no use. I have found that in all low-current, low BW amplifications the 27Mx has better performance than the TL-7x. If you can find it a 27M9 is slightly better that the 27M4. TI has a tlc27M9.

Kind regards,
J. L. King

[ivconic]

Yes, i forgot to mention that original 27M4 is returned to its place. It is ok. I removed it at the time and put TL084, but later when realised that 4016 was burned i returned 27M4 to its place. So...only original fet and 4016 were burned. 4016 is replaced with new one and instead original fet now is J303 on the place. That is my main point of interest; the fet and his role here. I had just few p channel fets here and by wild guess picked J303 among others. So now it is working quite proper there!? So..that provoked me to start thinking more about this power supply, to try to understand it better. Would like to analyze every each component there and its role...
Cose...i do really like the way how it is working. Was thinking to involve ps stage in some of my future works. Original fet now is not issue,knowing that it could be replaced with another type...hopefully.

[KingJL]

That is my main point of interest; the fet and his role here. I had just few p channel fets here and by wild guess picked J303 among others. So now it is working quite proper there!? So..that provoked me to start thinking more about this power supply, to try to understand it better. Would like to analyze every each component there and its role...

The purpose of the FET (along with the transistor circuit driving the gate) is to regulate the voltage to be 8V between the -/+ rails. Analog gnd is maintained between the 2 by the LM339 comparator circuit. I have used various PMOS in place of the VP0104. Just make sure that the Vds is sufficient, Rds-on is in range, and current rating is sufficient. If those are anywhere around the VP0104 specs, then it works!

Cose...i do really like the way how it is working. Was thinking to involve ps stage in some of my future works. Original fet now is not issue,knowing that it could be replaced with another type...hopefully.

I also like the way it works. The only limitation is the low current capability of the analog gnd (due to the LM339).
Regards,
J. L. King

[ivconic]

Indeed it is. Another thing that i like at 1265/66 is that nice audio. Kind of "avalanche" behavior when target gets close to coil. Hard to meet at any other brand. Just yesterday i realised that audio behavior is closelly tied to proper ps functioning. Now many things are more clear to me. I guess i forgathered to much with Tesoros designs and kind a used to think and observe things with their "eyes". That's why i had a lot of problems to understand this - Fisher's approach to problematics. All the time i fooled myself with that damn diode i put instead fet !??
That's why my handmade 1265 never worked properly! Now is time to fix it and try all over again to put some life in it!

[KingJL]

That's why my handmade 1265 never worked properly! Now is time to fix it and try all over again to put some life in it!

Remember to be carefull what op-amps you use or you will overload the PS analog gnd. If you use 3 TL074's (or TL084) you'll be drawing 30ma through the analog gnd vs 3 ma for a TLE2024 and 2 27M9's.
Also disregard all 1265/1266 schematic other that the official Fisher schematics posted on the forum. The 1266 reworked schematic has TOO many errors!
Regards,
J. L. King

[ivconic]

Remember to be carefull what op-amps you use or you will overload the PS analog gnd. If you use 3 TL074's (or TL084) you'll be drawing 30ma through the analog gnd vs 3 ma for a TLE2024 and 2 27M9's.
Also disregard all 1265/1266 schematic other that the official Fisher schematics posted on the forum. The 1266 reworked schematic has TOO many errors!
Regards,
J. L. King

I think i have TLE2024 here.
About schematic..yes i noticed also some differences between original Fisher schematic and other.