Fisher 1260 (1982)

[ivconic]

Just 30 minutes ago, winter fun with oldie Fisher 1260, produced in 1982. !!!

http://www.youtube.com/watch?v=z63UQ...1&feature=plcp

[ivconic]

Funny machine! Reminds me on 1265/1266 behavior.... audio response etc..
Yet it is quite different than 1265/66.
Quite different machine, quite different coil.
Coil was surprise for me!
TX=6.54mH , RX=6.55mH !!!
TX is center tapped.
TX/RX front end poted in epoxy!

This machine need 10% more sensitivity/depths to be very usable even nowdays.
I am reconsidering making DIY coil for it...

[Altra]

See attached, I believe it's a WL drawing!

[Altra]

A better copy

[ivconic]

Thanks Altra , i already have those for long time.
Yesteraday i analyzed schematic for few hours and compared it with present device.
Seems schematic is accurate, except the poted part that i can't compare.
My 1260 is with LM317 at charging input.
Also there is not 47k resistor between pins 2 and 3 at 3080 (as sugested on schematic).
What would i achieve if i add 47k there? Nothing! Because i checked that already!
Working frequency is 4.2kHz.
I am thinking to replace LM324 at channel with ... let's say LF347 and maybe gain some quality there?
Will see.

[homefire]

In the video, were those Metal Arrow Points I seen?

[ivconic]

In the video, were those Metal Arrow Points I seen?

Yes i detected 2 rusty and broken arrows. I couldn't expect nor predict where i will locate such finds so after getting signal i removed snow from soil and dug. Later when arrow was discovered i just showed it over removed soil. Camera is from my Nokia C1, very poor camera....

[ivconic]

Most recent photos:

[kt315]

Coil was surprise for me!

seems a coil is not 'fisher 1200 type'. more oldie, may be for LF990 553 555 series.
if you open any Polish forum you will see ALL-1 project.... know - it is what you want to find a data on your coil.
http://www.poszukiwanieskarbow.com/F...p?f=46&t=79250
thinking because it is clear the 555.

[ivconic]

seems a coil is not 'fisher 1200 type'. more oldie, may be for LF990 553 555 series.
if you open any Polish forum you will see ALL-1 project.... know - it is what you want to find a data on your coil.
http://www.poszukiwanieskarbow.com/F...p?f=46&t=79250
thinking because it is clear the 555.

Yes that's makes sense!

[Patrick]

Yes that's makes sense!

Bifilar wire.

[Altra]

Ivconic,

Something that I never noticed before in the schematic. Look at how pin 5 and 12 of one of the LM13700's is feeding back to the RX coil. I wonder if this was some sort of self nulling circuit? or just phase compensation for ground balance?


Thanks for the photos

[ivconic]

Thanks Patrick!
Wow, that's tough design!

...

Yes Altra, seems it is feedback.