Fisher 1266 PART 2

[ivconic]

Is it? I will check tomorrow.
Regards!

[Mikes]

Ivconic!







Best regards!

[ivconic]

Few other jobs finished so i am back on track again here. 1265 copy i made is still on the bench and waiting. By strange coincidence today i got original 1265 in descent shape. Only one thing miss - coil. Actually with this one came 8" White's (3900) coil!!! Ha,ha,ha! And it is working, but not that good as with original. Now i have almost perfect conditions to recheck all over again, to compare, measure...my 1265 copy simply MUST start to work good in next few days. PCB's were checked many times, there are no mistakes on those. Neither one mistake. So people who's interested in making copy of 1265 can freely use those pcb's...no mistakes at all.
First will recheck and compare original transformer and the one i used...than use scope and measure some signals and later check wirements on front panel...
If discover something wrong i will report here..

[ivconic]

Ha, i knew it! Today i made separatelly 1265 audio stage from schematic above and connected it to TGSL. It is working like hell! Just as i assumed; it is giving to TGLS quite new dimension. Now TGSL audio is extra strong and adjustable, also very rich and it has also sort of "bang" at clear signals!!! Ha,ha,ha! I wasted so many days trying to modd TGSL's audio...but all the time i had ready solution right in front of my eyes! Sheeesh!!
I had fear to meet some signal level isssues here, but i didnt. All is working perfectly from a very start. At TGSL's last stage, LM358 there is 27K resistor goes straight to MPSA13 base. I disconnected MPSA13 and composite signal from 4024, replace 27K with 10K and than connected straight to 1265 audio, and it is working like hell! Excellent! Best audio mod on TGSL so far!
But this experiment has much greater meaning for me; now i can understand much better philosophy of Fisher 1265 too. Actually i thought 1265 has something specially good soluted in previous stages that makes such good audio, such distincive and cognizable specific just to this serie. I was wrong.
Now with this audio stage TGSL is absolute superior in all the aspects to 1265. I will prepare schematic revision and post at TGSL thread...
This was real success..!
But if i wasnt dealing with 1265 last couple days, probably i would never got this fantastic idea....so..again proved that real work,experimenting and hard labour cant be ever replaced with plain philosophy. Proved so many times to me so far....

Now... few questions will remain opened for the future; with setup like this one TGSL will have 2 threshold stages...ha,ha... also 4024 lost part of important role....could be replaced with some simple divider 1/2 to run negative voltage generation stage...
and apetite now grows more; is it easier to achieve audio discrimination (2 tone) etc...etc....huh...neverending story!

[KingJL]

While on the subject of trouble shooting, I took some measurements of signals of different targets back when I was troubleshooting mine. These signals were the demod outpus for the resitive (R223/C210 junction) and the Disc (R224/C212 junction). I believe (memory may be faulty) that the test targets were 2 - 3 inches from coil. There are in attached txt file.

I just noticed that the formatting of the text file changed the columns of the ferrite readings. Here is a corrected txt file with the measurements. The first column of course is the target metal, the 2nd column is the approximate phase shift for the target, the 3rd column is the measurement of the resistive channel demod signal at the testpoint described in the previous post, the 4th column is the measurement of the disc channel demod signal at the test point described in the previous post.

There is a 208 degree phase differrence between the resistive channel and the Disc channel. When the GEB was adjusted correctly (so that ferrite gave 0 volts), the no target signal was leading by 7 degrees (~ -0.12v at the resistive channel test point).
Regards,
J. L. King

[ivconic]

I agree.
However; Spectrum&"relatives" do "pull out" rich audio from uPc, hard to make in amateur arrangement - makes those pretty out of range of our interest here. But this audio from Fisher is piece of cake to make.
I am deeply satisfied with what i got from TGSL on real field. Only one drawback - audio. So i tried to improve it many times. Latest audio mod turns to be best so far. But today i took another look on this one and got idea to try it with TGSL. It suppose to give quite new dimension to TGSL. Still early to say anything...but am just about to try it. I do expect some difficulties here, some signal level issues...will see. Better to stop talking for now.
If gain some success i will post my experiences on the other thread.
Back to 1265...well, considering all we talked about here finally i can suspect only pcb or some broken component... transformer is ok, quratz is ok, coil is ok, schematic seem to be ok...pfffff!
These days i will have to sit and recheck all over again from the very start.
Also i will keep on my mind all your hints and datas you offered here.
Until than...
Regards!

[KingJL]

Pretty interesting audio we have here...it is starting to itch my imagination !
Was thinking to experiment a bit with this and TGSL...hmmm...

I agree! I am impressed with a lot of the "old" Fisher implementations. Too bad that the new stuff just does not stack up. I like a lot of the "old" Whites implementations also. The Spectrum's are hard to beat.

[KingJL]

I also remember low side:high side step up ratio was 1:10. You don't want to go above this ratio as you can damage the comparators.

Found my notes! 1 ohm and 40 ohms. Suitable part, Mouser part # 42TL008-RC.
Regards,
J. L. King

[ivconic]

Hopefully not. Seems i picked up most suitable one.
Other things you said - excellent reference, many thanks!
Be back later...

P.S.
Pretty interesting audio we have here...it is starting to itch my imagination !
Was thinking to experiment a bit with this and TGSL...hmmm...

[KingJL]

As near as I can tell without tearing out my unit the measurements were: low side (TX path), ~1 ohm; high side (comparator inputs), ~40 ohm.

I also remember low side:high side step up ratio was 1:10. You don't want to go above this ratio as you can damage the comparators.
Regards,
J. L. King

[KingJL]

While on the subject of trouble shooting, I took some measurements of signals of different targets back when I was troubleshooting mine. These signals were the demod outpus for the resitive (R223/C210 junction) and the Disc (R224/C212 junction). I believe (memory may be faulty) that the test targets were 2 - 3 inches from coil. There are in attached txt file.

A point to clarify, not all the metals were actually tested. The ferrite, small nail, large nail, gold ring, dime, and quarter were actually measured. The others were interpolated from a phase chart that I have. I adjusted the GEB for 0 volts on resistive test point with ferrite at 3 inches from coil.
Regards,
J. L. King

[KingJL]

BTW what are the resistances of your transformer?

As near as I can tell without tearing out my unit the measurements were: low side (TX path), ~1 ohm; high side (comparator inputs), ~40 ohm.
Regards,
J. L. King

[KingJL]

What is your opinion on transformer? In schematic is noted some 800 ohms!?!? Ha,ha!
I dont think is possible to make such small transformer with such HUGE resistance, must be a mistake. What do you think?

The 8ohm/800ohm are impedance not resistance.

BTW what are the resistances of your transformer?

I think I have that somewhere, I will search. It is a typical audio transformer. I had researched a part that had the right specs when I was anticpating building this (before I came across one at an extremely affordable price).

While on the subject of trouble shooting, I took some measurements of signals of different targets back when I was troubleshooting mine. These signals were the demod outpus for the resitive (R223/C210 junction) and the Disc (R224/C212 junction). I believe (memory may be faulty) that the test targets were 2 - 3 inches from coil. There are in attached txt file.
Regards,
J. L. King

[ivconic]

"...Thinking on this , it actually makes sense to use the MPSU51 in the battery check mode. As the battery discharges down to close to 8-9V, the MPSU51 current will decrease and give weaker audio, but with fully charged battery will limit current during battery check and keep from "blowing" ears and speaker...."

Yes, agree, that makes sense also. Well...i will distinguish MPSU51 doubt after fixing major problem..not so urgent right now. Pitty i dont have any original 1265 right now at me.
What is your opinion on transformer? In schematic is noted some 800 ohms!?!? Ha,ha!
I dont think is possible to make such small transformer with such HUGE resistance, must be a mistake. What do you think?
BTW what are the resistances of your transformer?

[KingJL]

About other of your notes...many thanks i will check them all.

A quick check to see if everything in the front end is working correctly, would be to check the junction of R223 & C210 while varying the GEB from limit to limit. It should result with the voltage going both positive and negative with 0v somewhere close to the middle. If this is the case and the components close to the original, then everything in the front end should be ok. With no target, if GEB is set for 0V at the junction of R223 and C210, the voltage at junction of R224 & C212 (Disc channel) should be ~ -0.47V.

This will verify the the inputs to the resistve and disc channels are getting the correct signals.

Regards,
J. L. King